Research Article Wettability Effects on Capillary Pressure...
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Research Article Wettability Effects on Capillary Pressure, Relative Permeability, and Irredcucible Saturation Using Porous Plate Olugbenga Falode and Edo Manuel Department of Petroleum Engineering, University of Ibadan, Ibadan 200284, Nigeria Correspondence should be addressed to Olugbenga Falode; [email protected] Received 24 February 2014; Revised 19 June 2014; Accepted 20 June 2014; Published 17 August 2014 Academic Editor: Chih-Ming Kao Copyright © 2014 O. Falode and E. Manuel. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. An understanding of the mechanisms by which oil is displaced from porous media requires the knowledge of the role of wettability and capillary forces in the displacement process. e determination of representative capillary pressure ( ) data and wettability index of a reservoir rock is needed for the prediction of the fluids distribution in the reservoir: the initial water saturation and the volume of reserves. is study shows how wettability alteration of an initially water-wet reservoir rock to oil-wet affects the properties that govern multiphase flow in porous media, that is, capillary pressure, relative permeability, and irreducible saturation. Initial water-wet reservoir core samples with porosities ranging from 23 to 33%, absolute air permeability of 50 to 233 md, and initial brine saturation of 63 to 87% were first tested as water-wet samples under air-brine system. is yielded irreducible wetting phase saturation of 19 to 21%. e samples were later tested aſter modifying their wettability to oil-wet using a surfactant obtained from glycerophtalic paint; and the results yielded irreducible wetting phase saturation of 25 to 34%. From the results of these experiments, changing the wettability of the samples to oil-wet improved the recovery of the wetting phase. 1. Introduction Wettability refers to the tendency of one fluid to spread on or adhere to a solid surface in the presence of immiscible fluids as shown in Figure 1 [1]. In natural porous media, the wettability varies from point to point depending upon the surface roughness [2], immobile adsorbed liquid layers [3], and the adsorptive properties of the mineral constituents. Anderson reported that coal, graphite, sulfur, talc, talc- like silicates, and many sulfides are probably neutrally wet to oil-wet [4]. On the other hand, most common aquifer materials such as quartz, carbonates, and sulfates are strongly water wet. It is the wettability of the reservoir rock that controls the distribution of oil and water and affects their movement through pore spaces. Understanding wettability in porous media is, by itself, a difficult problem. Controlling it to modify the behavior of reservoir rock presents a more complex problem. Numerous methodologies for studying, measuring, and altering the wettability of reservoir rocks are found in literature. No satisfactory method exists for in situ measurement of wettability, and therefore it is necessary to estimate the wettability of reservoir rocks from laboratory measurements. It is known that a porous material can be defined as water- wet, oil-wet, or mixed-wet. e degree to which a reservoir is one or another of these can be determined by considering the capillary pressure curve, or by characterizing it in terms of wettability indices. Several experimental procedures have been proposed to assign quantitative wettability indexes to reservoir rock surfaces. e most recent of these proposals are those of Morrow [5], Graue et al. [6], and Derahman and Zahoor [7]. ese indexes are designed to show a continuous variation from the preferential oil-wet to the preferential water-wet systems. ey require measuring some property of the rock which is a function of surface wettability. e quantities are measured on unaltered core material and compared with values obtained for known oil-wet and water-wet extremes on the same material. ese methods are useful but are Hindawi Publishing Corporation Journal of Petroleum Engineering Volume 2014, Article ID 465418, 12 pages http://dx.doi.org/10.1155/2014/465418
Transcript of Research Article Wettability Effects on Capillary Pressure...
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Research ArticleWettability Effects on Capillary Pressure Relative Permeabilityand Irredcucible Saturation Using Porous Plate
Olugbenga Falode and Edo Manuel
Department of Petroleum Engineering University of Ibadan Ibadan 200284 Nigeria
Correspondence should be addressed to Olugbenga Falode falodeliasyahoocom
Received 24 February 2014 Revised 19 June 2014 Accepted 20 June 2014 Published 17 August 2014
Academic Editor Chih-Ming Kao
Copyright copy 2014 O Falode and E Manuel This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
An understanding of the mechanisms by which oil is displaced from porous media requires the knowledge of the role of wettabilityand capillary forces in the displacement process The determination of representative capillary pressure (119875
119888) data and wettability
index of a reservoir rock is needed for the prediction of the fluids distribution in the reservoir the initial water saturation andthe volume of reserves This study shows how wettability alteration of an initially water-wet reservoir rock to oil-wet affects theproperties that governmultiphase flow in porous media that is capillary pressure relative permeability and irreducible saturationInitial water-wet reservoir core samples with porosities ranging from 23 to 33 absolute air permeability of 50 to 233md and initialbrine saturation of 63 to 87 were first tested as water-wet samples under air-brine system This yielded irreducible wetting phasesaturation of 19 to 21 The samples were later tested after modifying their wettability to oil-wet using a surfactant obtained fromglycerophtalic paint and the results yielded irreducible wetting phase saturation of 25 to 34 From the results of these experimentschanging the wettability of the samples to oil-wet improved the recovery of the wetting phase
1 Introduction
Wettability refers to the tendency of one fluid to spread onor adhere to a solid surface in the presence of immisciblefluids as shown in Figure 1 [1] In natural porous media thewettability varies from point to point depending upon thesurface roughness [2] immobile adsorbed liquid layers [3]and the adsorptive properties of the mineral constituentsAnderson reported that coal graphite sulfur talc talc-like silicates and many sulfides are probably neutrally wetto oil-wet [4] On the other hand most common aquifermaterials such as quartz carbonates and sulfates are stronglywater wet
It is the wettability of the reservoir rock that controlsthe distribution of oil and water and affects their movementthrough pore spaces Understanding wettability in porousmedia is by itself a difficult problem Controlling it tomodify the behavior of reservoir rock presents a morecomplex problem Numerous methodologies for studyingmeasuring and altering the wettability of reservoir rocks are
found in literature No satisfactory method exists for in situmeasurement of wettability and therefore it is necessary toestimate the wettability of reservoir rocks from laboratorymeasurements
It is known that a porousmaterial can be defined aswater-wet oil-wet ormixed-wet The degree to which a reservoir isone or another of these can be determined by considering thecapillary pressure curve or by characterizing it in terms ofwettability indices
Several experimental procedures have been proposedto assign quantitative wettability indexes to reservoir rocksurfaces The most recent of these proposals are those ofMorrow [5] Graue et al [6] and Derahman and Zahoor [7]These indexes are designed to show a continuous variationfrom the preferential oil-wet to the preferential water-wetsystems They require measuring some property of the rockwhich is a function of surface wettability The quantities aremeasured on unaltered core material and compared withvalues obtained for known oil-wet and water-wet extremeson the same material These methods are useful but are
Hindawi Publishing CorporationJournal of Petroleum EngineeringVolume 2014 Article ID 465418 12 pageshttpdxdoiorg1011552014465418
2 Journal of Petroleum Engineering
Air
Water
Glass
Mercury
120579 lt 90∘ 120579 gt 90∘
120579 120579
Figure 1 Wetting fluid (water) and nonwetting fluid (mercury)
Secondary drainage (forced)
Primary drainage (forced)
Imbibition(spontaneous)
Secondary
(spontaneous)
Imbibition(forced)
minusve
+ve
A1
A2
0
0 10
SorSwi
Pc
Sw
ΔSos
ΔSws
drainage
Figure 2 Capillary pressure diagram used to characterize wettabil-ity
semiempirical in nature They have the disadvantage that themeasured quantities may be functions of other variables inaddition to surface wettability
(a) Amott IndicesReferring to Figure 2 the Amott indices aredefined as
119868119900=
Δ119878119900119904
1 minus 119878119908119894minus 119878119900119903
119868119908=
Δ119878119908119904
1 minus 119878119908119894minus 119878119900119903
(1)
If the material is completely water-wet then 119868119900= 0 and 119868
119908=
1 If the material is strongly oil-wet then 119868119900= 1 and 119868
119908= 0
119868119900is the displacement-by-oil ratio and is the water volume
displaced by spontaneous oil imbibition relative to thetotal water volume displaced by oil imbibition (spontaneousand forced) 119868
119908is the displacement-by-water ratio and is
the oil volume displaced by spontaneous water imbibitionrelative to the total oil volume displaced by water imbibition(spontaneous and forced) For connected pathways of oil andwater then both indices can be greater than zero
(b) USBM Wettability Index This index is based on the ratioof the two areas representing forced imbibition in Figure 2
119873119908= log(1198601
1198602
) (2)
Solid
Interface
120579
120601
P998400P998400998400
R
r =R
cos(120579 + 120601)
Fluid (998400)Fluid (998400998400)
Figure 3 Fluid interface in a tapered capillary tube
The range is from +infin for a completely water-wet materialto minusinfin for a completely oil-wet material Typical values are inthe range of minus15 to +10 In general this index is not used verymuch
In this work the wettability of the tested samples was notdetermined Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and since thetested samples are quartz and carbonates materials it wastherefore assumed that they are water-wet
When two immiscible fluids are in contact in the inter-stices of a porous medium a discontinuity in pressureexists across the interface separating them The differencein pressure (119875
119888) is called capillary pressure The capillary
pressure is dependent on the interfacial tension pore sizeandwetting angle Capillary pressure is themost fundamentalrockfluid property in multiphase flow just as porosity andpermeability are for single phase flow in oil and gas reser-voirs [8] Capillary pressure curves directly determine theirreducible water saturation residual oil saturation and rockwettability and can be used to determine water oil contactpoint and approximate oil recovery Figure 2 is a capillarypressure diagram showing how it can be used to characterizewettability and the capillary pressure is the difference inpressure (119875
119888) as exemplified by Figure 3 where the porous
medium can be described by a capillary tube where a clearinterface exists between the immiscible fluids Water floodperformance is also significantly affected by the capillarypressure of the rock [9]
By definition the capillary pressure is the nonwettingfluid pressure minus the wetting fluid pressure
119875119888= 119875non-wetting minus 119875wetting (3)
The capillary pressure 119875119888can be calculated by the Laplace
equation
119875119888= 120590(
1
1199031
+1
1199032
) (4)
The capillary pressure equation can be expressed in terms ofthe surface and interfacial tension by
119875119888=2120590 cos 120579
119903 (5)
where 120590 is interfacial tension between the two fluids and1199031and 119903
2are principle radii of curvature and 120579 is the
Journal of Petroleum Engineering 3
Figure 4 ULTRAPORE-300 assembly
contact angle Capillary pressure data are not only importantfor obtaining reservoir rock properties such as pore sizedistribution permeability andwater saturation profile withinthe oil reservoir but also provide important information forwater flooding designs and reservoir simulation studies
Capillary pressure is typically measured in the laboratoryby mercury injection porous plate or centrifugation tech-niquesThe porous platemethod (PP) has been used for yearsin acquiring reliable capillary pressure data representative ofreservoir rock fluid properties In recent years the methodis also found to be reliable and subject to less experimentalerrors and analysis when used for electrical resistivity (RI)measurements as well A major problem has been the longtime scales required for achieving reliable data
The mercury injection technique is fast and can reachvery high capillary pressure but the test uses nonrepresenta-tive fluid mercury and it is destructive whereas the centrifu-gation technique [10] uses reservoir fluids and decreases theequilibrium time by using high centrifugal forces
In this study the porous plate method was used inacquiring the capillary pressure data of the tested samples
The term relative permeability refers to the phase perme-ability relative to the absolute permeability k
119896119903119900=119896119900
119896 119896
119903119908=119896119908
119896 119896
119903119892=
119896119892
119896 (6)
Several mathematical models have been proposed to inferrelative permeability from capillary pressure data In 2008Derahman andZahoor demonstrated amethodof calculatingthe permeability using capillary pressure curves measuredby mercury injection [7] A tortuosity factor in the modelwas earlier introduced and the method was modified byrepresenting capillary pressure curve as a power law functionof the wetting phase saturation [11ndash13] As mentioned pre-viously capillary pressure and relative permeability are bothmeasured in the laboratory however it is time consumingand expensive to both in many cases For the purpose of thisstudy the empirical Brooks-Corey-Burdine formulae [11ndash13]are used
119896119903119908= 1199044
119890119908
119896119903119899119908
= (1 minus 119904119890119908)2
(1 minus 1199042
119890119908)
119904119890119908=119904119908minus 119904119903119908
1 minus 119904119903119908
(7)
Figure 5 WINPORE snapshot
Figure 6 Frank Jones liquid permeameter
where 119870119903119908
and 119870119903119899119908
are the wetting phase and nonwettingphase relative permeability respectively 119878
119890119908 119878119903119908 and 119878
119908are
the effective wetting phase saturation wetting phase residualsaturation and wetting phase saturation respectively
2 Justification for This Study
Several studies have been conducted on wettability reversaleffects on oil recovery using different surfactants to deliber-ately improve oil recovery however the literature is sparseon wettability alteration that results from contact with thecomponents of corrosion inhibitors or paints the focus of thisstudy Moreover no study of such has been reported on theNiger Delta formations
3 Brief Literature Cited
Sayari and Blunt [14] performed benchmark experimentson multiphase flow in which they investigated the effectof wettability on relative permeability capillary pressureelectrical resistivity and nuclear magnetic resonance (NMR)In that study they compared the results obtained from a suiteof experimental measurements on well characterized systemsthat studies relevant properties such as capillary pressurerelative permeability NMR response and resistivity indexwith numerical predictions using pore-scale modeling wherethe pore space was imaged with micro-CT scanning
Al-Garni and Al-Anazi [15] correlated the wettabilitycapillary pressure and initial fluids saturation for SaudiArabia crude oil In their study they correlated irreducibleoil saturation and capillary pressures using rock centrifugemeasurements for Berea rock Sandstone samples on Saudicrude oils during drainage and imbibition cycles by varying
4 Journal of Petroleum Engineering
Figure 7 Saturator
Core
Porous plate
PressuresupplyPressure
regulator
PD
Manometer
Figure 8 Porous plate diagram
each time the wettability of the tested samples using differentSaudi oils (heavy medium and light)
Green et al [16] presented a new method of determiningthe capillary pressure by directmeasurement of the saturationusing magnetic resonance imaging (MRI) He used theHassler and Brunner equation at each radial position inthe rock to calculate the capillary pressure which togetherwith saturation measured with MRI at each position directlyproduces a capillary pressure curve with as few as singlecentrifuge equilibrium [10] The technique is reported to berapid accurate and ideally suited to study ldquotightrdquo or lowpermeability rocks
Chen et al [17] discussed on NMR wettability indiceseffect of OBM on wettability and NMR responses The find-ings of that study were that cationic surfactant dodecylaminealters the wettability of glass slide surface while anionicsurfactant stearic acid alters the wettability ofmarble surfaceThey were able to correlate the proposed NMR wettabilityindices (water index oil index or combined index) with thetraditional Amott-Harvey indices suggesting that quantita-tive information about rock wettability can be gained fromNMRmeasurements
Figure 9 Ceramic platecapillary pressure cell
OrsquoCarroll et al [18] in their study predicted two-phasecapillary pressuresaturation relationships in fractional wet-tability systems They presented a new two-phase capillarypressuresaturation model for application to the predictionof primary drainage and imbibition relations in fractionalwettability media That new model was based on extensionof Leverett scaling theory
Bekri et al [19] studied the effect of wettability on thepetrophysical parameters of vuggy carbonates In their studythey modelled a dual network for dual porosity rocks whichsatisfactorily reproduced the capillary pressure curve theporosity and the permeability determined experimentallyon a double porosity rock They found that the contrastbetween primary and secondary pore space characteristicshas a major effect on both the capillary pressure and therelative permeabilities
Li and Firoozabadi [20] showed that if the wettability ofporous media can be altered from preferential liquid wettingto preferential gas-wetting then gas well deliverability in gascondensate reservoirs can be increased
Hui and Blunt [21] studied the effects of rock wettabilityon the flow of oil water and gas in hydrocarbon reservoirsThey described the three-phase fluid configurations anddisplacement processes in a pore of polygonal cross section
4 Methodology
The present work relies on laboratory experimental resultsobtained from routine and special core analysis In conduct-ing the routine core analysis properties such as porositypermeability and the percentage saturation of the testedsample were determined while only the capillary pressuredata of the tested samples were determined during the specialcore analysis In this section we describe the experimentalprocedures that were used in determining the above rockproperties
41 Routine Core Analysis
411 Porosity In this study the ULTRAPORE-300 as shownin Figure 4 was used to estimate the absolute porosityof the four (04) tested samples The porosity of a rock ismathematically defined as
120601 =pore volumebulk volume
lowast 100 () (8)
Journal of Petroleum Engineering 5
Figure 10 Water-wet samples loaded into ceramic plate
In this study the ULTRAPORE-300 was used to estimatethe absolute porosity of the four (04) tested samples TheULTRAPORE-300 system software (WINPORE) computedthe grain volume pore volume and the grain density ofthe samples The testing procedure used in determining thegrain volume and pore volume is as follows
412 Grain Volume Determination
(i) The samples were dried and weighted after whichthey were loaded one after the other inside a 11210158401015840diameter matrix cup
(ii) The ULTRAPORE-300 system software (WINPORE)was first calibrated to obtain a reference volume forgrain volume measurement
(iii) Nitrogen gas was allowed to flow into the 11210158401015840diameter matrix cup system at a pressure P (psi)
(iv) The system generated a set of corresponding volumeat that pressure P for each sample loaded and used theBoylersquos law equation in computing the samples grainvolume
413 Pore Volume Determination
(i) The pore volume of the samples was determinedsimilarly as the grain volume except that the systemsoftware was calibrated for pore volume instead ofgrain volume
(ii) The samples were then loaded into a rubber bootplaced inside a hydrostatic core holder at an overbur-den pressure of 200 psi where the nitrogen gas wasallowed to flow in the core holder to fill the porespaces of the samples at equilibrium
(iii) The system software (WINPORE) generated then thepore volume of the samples (Figure 5) The graindensity of each sample was computed by the systemsoftware The bulk volume of the samples was com-puted empirically
414 Air Permeability Determination The testing procedureused is as follows
(i) The samples were loaded inside a core holder con-nected to the gas permeameter (Figure 6)
(ii) Nitrogen gas was allowed to flow into the samplesusing a regulator to obtain a laminar flow regimeThelaminagr flow regime was determined using a bubbleflow meter to ascertain that the flow rate does notexceed 1 ccs
(iii) Using the bubble-tool flow meter the flow rate atwhich the gas flow through the samples was deter-mined using the flow rate definition
(iv) The air permeability was then computed from theequation given below
119896 =2000119875
119887lowast 119876 lowast 120583 lowast (119897119860)
(119875 + 119875119887)2
minus 1198752
119887
(9)
where 119875119887is barometric pressure (atm) 120583 is119873
2viscosity (cp)
P is measured pressure (atm) 119897 is sample length (cm) 119876 isflow rate (ccs) and A is sample area (cm2)
415 Percentage Saturation Determination This property isexpressed mathematically by the following relationship
fluid saturation = total volume of fluidpore volume
lowast 100 () (10)
Saturation is a direct measure of the fluid content of theporous rock It therefore directly influences the hydrocarbonstorage capacity of the reservoir
In the pores of oil or gas reservoirs there always remainssome water that was there before the hydrocarbon entrap-ment At any time during the life of an oil or gas reservoirthe following relationship must hold true
119878119900+ 119878119908+ 119878119892= 10
119878119900=
oil volumepore volume
=119881119900
119881119901
119878119908=water volumepore volume
=119881119908
119881119901
119878119892=
gas volumepore volume
=
119881119892
119881119901
(11)
6 Journal of Petroleum Engineering
(a) Weighing saturated water-wet sample before wettability alteration (119878unmod)
(b) Weighing saturated (light oil) after wettability alteration to oil-wet (119878 mod )
Figure 11
Table 1 Routine core analysis results
Core 119871 119863 BV GV GD Porosity 119878119908119894
119878119900119894
119870119886
(cm) (cm) (cc) (cc) (gcc) () () () (md)102 716 386 8416 2572 268 3056 6279 7088 139546 681 383 7859 5251 265 3318 7198 6458 23184 625 378 7023 4902 264 3020 5941 5875 223X 513 388 6090 4641 269 2379 8731 8627 50
Figure 12 Samples loaded into the ceramic plate after wettability alteration to oil-wet
Journal of Petroleum Engineering 7
35
30
25
20
15
10
5
0
Pc
(psi)
Air-oilAir-brine
K = 13929
Swi = 6279Swir = 1913
120601 = 3056Soi = 7088Sor = 2913
20 30 40 50 60 70 80 90 100
Sw ()
Sample 102 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
35
30
25
20
15
10
5
0
Pc
(psia
)Air-oilAir-brine
K = 231mdSwi = 7198Swir = 1593
120601 = 3318Soi = 6458Sor = 2637
10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 546 capillary pressure versus saturationfor both air-brine and air-oil system
(b)
Figure 13 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod Capillary pressure (119875
119888) versus Saturation (119878
119908) curves
It is common for oil or gas saturation to be zero but watersaturation is always greater than zero
The percentage saturation of the tested samples wasmeasured as follow
(i) The dry weight of the samples was recorded(ii) The samples were loaded in the saturator and air was
evacuated from the saturator for 30 minutes usingvacuum pump
(iii) The saturator was filled with the saturating fluid(brine or light oil) at a pressure of 1000 psi for 24hours after which the samples were removed fromthe saturator and their net weight were recorded(Figure 7)
42 Special Core Analysis For the purpose of this work onlythe capillary pressure of the tested samples was determinedfrom the special core analysis The porous plate method wasused for that purpose In doing so a set of capillary pressuredata was acquired under different wettability conditions Thefirst set of capillary pressure data was acquired for water-wetcore sample while the second set of capillary pressure datawas acquired after the wettability of the samples was alteredto oil wet by smearing paint (alkyd resins) on the surface ofthe tested samples
421 Capillary Pressure Measurement Using the PorousPlate Method
Testing Procedure The semipermeable porous plate was firstprepared (Figure 8) Plates for oil and brine were separated
The plates were first saturated with distilled water or lightmineral oil and then tested for leaks
Once saturated the plate was not allowed to dry becausefractures will often occur Before use the plate was flushedwith the brine or oil that the samples are saturated withThis was accomplished in the cell by pouring some of theliquid into the cell (Figure 9) Cover the plate with 1210158401015840 ofliquid Close the cell and apply a 35 psi air pressure Pressureis generally provided by a pressure gauge control panel whichhas gauges ranging in pressure from 1 psi to 50 psi
Once the plate has been prepared and the samplessaturated they are now loaded into the cell Place a discof white clean tissue paper on one end face of the sampleto prevent possible contamination and damage to thewettability characteristics of the samples The disc shouldbe of the same diameter as the core sample The tissue willensure that good capillary contact is made Once the samplesare in place in the cell (Figure 10) clean the o-rings on thetop and bottom of the barrel Carefully lower the barrel onthe porous plate and samples and align it to the base Gentlyplace the lid on the barrel insert the screw that holds it inplace and do not overtighten
Connect the air pressure source to the valve on the lidPreset the regulator and gauge to the first pressure (1 psi)gently open the valve leading from the pressure panel andlisten for the sound of air flowing into the cell Close theexhaust valve Put the drain line into a small beaker partiallyfilled with water and open the valve in the base of the cellThe pressures used routinely in air-brine system are 1 2 58 15 and 35 psi Pressure is maintained until equilibrium isreached This is determined by weighing the samples on suc-cessive days until the weights of all the samples are constant
8 Journal of Petroleum Engineering
K = 223mdSwi = 5941Swir = 1317
120601 = 3020Soi = 5875Sor = 2472
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
0 10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 84 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
K = 50mdSwi = 8731Swir = 2079
120601 = 2379Soi = 8627Sor = 3400
Sample X capillary pressure versus saturation
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
20 30 40 50 60 70 80 90 100
Sw ()
for both air-brine and air-oil system
(b)
Figure 14 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod
Table 2 Air-brine capillary pressures and saturations of the samples(119878unmod)
119875119888(psi) 119878
119882() 119878
119882() 119878
119882() 119878
119882()
Sample 102 Sample 546 Sample 84 Sample X1 9839 9824 9825 99052 9090 9185 9119 91945 8006 8002 8206 82618 6272 6319 6571 671915 4322 4177 4254 487735 1913 1593 1317 2079
Table 3 Air-oil capillary pressures and saturations of the samples(119878 mod )
119875119888(psi) 119878
119900() 119878
119900() 119878
119900() 119878
119900()
Sample 102 Sample 546 Sample 84 Sample X1 9890 9822 9856 1002 9616 9365 9494 98405 9051 8557 8676 90648 8124 7185 7095 813615 6045 5024 5161 627235 2913 2637 2472 3400
To open the cell close the drain valve and the pressurevalve Slowly open the exhaust valve and once the pressure hasbeen vented the cell can be safely openedThe test is completeonce the weights have been obtained at equilibrium for thelast pressure setting After the test is complete the porousplate must be cleaned and prepared for storage or reuse
The testing procedure described above was used for air-brine system whereby the wettability of the core sample wasnot altered (water wet samples) Air-oil tests are performedin the same manner as described above except that a low
viscosity refined mineral oil such as Isopar was used tosaturate the samples and the porous plate Because air-brineand air-oil systems have different surface tension values thepressure settings were different and 05 1 2 5 8 and 15 psiwere used for air-oil system
422 Air-Brine System Capillary Pressure Measurement Inthis study the procedure described above was used for air-brine system in acquiring the capillary pressure data of thecore samples
423 Air-Oil System Capillary Pressure Measurement Air-oil tests are performed in the same manner as for the air-brine system except that the samples and the porous platewere saturated with oil and the pressure settings are 05 12 5 8 and 12 psi In this work the air-oil system procedureof measuring capillary pressure was as for the air-brineexcept that the wettability of the core samples was altered tooil-wet
424 Wettability Modification Glycerophtalic paint (Sigma-Aldrich Inc) was dissolved by stirring overnight in acetoneat room temperature Then the solution was placed in a60 cm3 syringe with a 20-gauge blunt tip needle The tip-to-substrate distance was set at 20 cm and the solution wasflowed on the surface of the samples at a rate of 15mLhrwith a syringe pump (KDS100 KD Scientific Inc) as shownin Figures 11(a) and 11(b) The paint solutions used forwettabilitymodification in the experimental work were 2mmthick Samples were then loaded into the ceramic plate afterwettability alteration (Figure 12) Samples whose surfaces
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
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![Page 2: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/2.jpg)
2 Journal of Petroleum Engineering
Air
Water
Glass
Mercury
120579 lt 90∘ 120579 gt 90∘
120579 120579
Figure 1 Wetting fluid (water) and nonwetting fluid (mercury)
Secondary drainage (forced)
Primary drainage (forced)
Imbibition(spontaneous)
Secondary
(spontaneous)
Imbibition(forced)
minusve
+ve
A1
A2
0
0 10
SorSwi
Pc
Sw
ΔSos
ΔSws
drainage
Figure 2 Capillary pressure diagram used to characterize wettabil-ity
semiempirical in nature They have the disadvantage that themeasured quantities may be functions of other variables inaddition to surface wettability
(a) Amott IndicesReferring to Figure 2 the Amott indices aredefined as
119868119900=
Δ119878119900119904
1 minus 119878119908119894minus 119878119900119903
119868119908=
Δ119878119908119904
1 minus 119878119908119894minus 119878119900119903
(1)
If the material is completely water-wet then 119868119900= 0 and 119868
119908=
1 If the material is strongly oil-wet then 119868119900= 1 and 119868
119908= 0
119868119900is the displacement-by-oil ratio and is the water volume
displaced by spontaneous oil imbibition relative to thetotal water volume displaced by oil imbibition (spontaneousand forced) 119868
119908is the displacement-by-water ratio and is
the oil volume displaced by spontaneous water imbibitionrelative to the total oil volume displaced by water imbibition(spontaneous and forced) For connected pathways of oil andwater then both indices can be greater than zero
(b) USBM Wettability Index This index is based on the ratioof the two areas representing forced imbibition in Figure 2
119873119908= log(1198601
1198602
) (2)
Solid
Interface
120579
120601
P998400P998400998400
R
r =R
cos(120579 + 120601)
Fluid (998400)Fluid (998400998400)
Figure 3 Fluid interface in a tapered capillary tube
The range is from +infin for a completely water-wet materialto minusinfin for a completely oil-wet material Typical values are inthe range of minus15 to +10 In general this index is not used verymuch
In this work the wettability of the tested samples was notdetermined Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and since thetested samples are quartz and carbonates materials it wastherefore assumed that they are water-wet
When two immiscible fluids are in contact in the inter-stices of a porous medium a discontinuity in pressureexists across the interface separating them The differencein pressure (119875
119888) is called capillary pressure The capillary
pressure is dependent on the interfacial tension pore sizeandwetting angle Capillary pressure is themost fundamentalrockfluid property in multiphase flow just as porosity andpermeability are for single phase flow in oil and gas reser-voirs [8] Capillary pressure curves directly determine theirreducible water saturation residual oil saturation and rockwettability and can be used to determine water oil contactpoint and approximate oil recovery Figure 2 is a capillarypressure diagram showing how it can be used to characterizewettability and the capillary pressure is the difference inpressure (119875
119888) as exemplified by Figure 3 where the porous
medium can be described by a capillary tube where a clearinterface exists between the immiscible fluids Water floodperformance is also significantly affected by the capillarypressure of the rock [9]
By definition the capillary pressure is the nonwettingfluid pressure minus the wetting fluid pressure
119875119888= 119875non-wetting minus 119875wetting (3)
The capillary pressure 119875119888can be calculated by the Laplace
equation
119875119888= 120590(
1
1199031
+1
1199032
) (4)
The capillary pressure equation can be expressed in terms ofthe surface and interfacial tension by
119875119888=2120590 cos 120579
119903 (5)
where 120590 is interfacial tension between the two fluids and1199031and 119903
2are principle radii of curvature and 120579 is the
Journal of Petroleum Engineering 3
Figure 4 ULTRAPORE-300 assembly
contact angle Capillary pressure data are not only importantfor obtaining reservoir rock properties such as pore sizedistribution permeability andwater saturation profile withinthe oil reservoir but also provide important information forwater flooding designs and reservoir simulation studies
Capillary pressure is typically measured in the laboratoryby mercury injection porous plate or centrifugation tech-niquesThe porous platemethod (PP) has been used for yearsin acquiring reliable capillary pressure data representative ofreservoir rock fluid properties In recent years the methodis also found to be reliable and subject to less experimentalerrors and analysis when used for electrical resistivity (RI)measurements as well A major problem has been the longtime scales required for achieving reliable data
The mercury injection technique is fast and can reachvery high capillary pressure but the test uses nonrepresenta-tive fluid mercury and it is destructive whereas the centrifu-gation technique [10] uses reservoir fluids and decreases theequilibrium time by using high centrifugal forces
In this study the porous plate method was used inacquiring the capillary pressure data of the tested samples
The term relative permeability refers to the phase perme-ability relative to the absolute permeability k
119896119903119900=119896119900
119896 119896
119903119908=119896119908
119896 119896
119903119892=
119896119892
119896 (6)
Several mathematical models have been proposed to inferrelative permeability from capillary pressure data In 2008Derahman andZahoor demonstrated amethodof calculatingthe permeability using capillary pressure curves measuredby mercury injection [7] A tortuosity factor in the modelwas earlier introduced and the method was modified byrepresenting capillary pressure curve as a power law functionof the wetting phase saturation [11ndash13] As mentioned pre-viously capillary pressure and relative permeability are bothmeasured in the laboratory however it is time consumingand expensive to both in many cases For the purpose of thisstudy the empirical Brooks-Corey-Burdine formulae [11ndash13]are used
119896119903119908= 1199044
119890119908
119896119903119899119908
= (1 minus 119904119890119908)2
(1 minus 1199042
119890119908)
119904119890119908=119904119908minus 119904119903119908
1 minus 119904119903119908
(7)
Figure 5 WINPORE snapshot
Figure 6 Frank Jones liquid permeameter
where 119870119903119908
and 119870119903119899119908
are the wetting phase and nonwettingphase relative permeability respectively 119878
119890119908 119878119903119908 and 119878
119908are
the effective wetting phase saturation wetting phase residualsaturation and wetting phase saturation respectively
2 Justification for This Study
Several studies have been conducted on wettability reversaleffects on oil recovery using different surfactants to deliber-ately improve oil recovery however the literature is sparseon wettability alteration that results from contact with thecomponents of corrosion inhibitors or paints the focus of thisstudy Moreover no study of such has been reported on theNiger Delta formations
3 Brief Literature Cited
Sayari and Blunt [14] performed benchmark experimentson multiphase flow in which they investigated the effectof wettability on relative permeability capillary pressureelectrical resistivity and nuclear magnetic resonance (NMR)In that study they compared the results obtained from a suiteof experimental measurements on well characterized systemsthat studies relevant properties such as capillary pressurerelative permeability NMR response and resistivity indexwith numerical predictions using pore-scale modeling wherethe pore space was imaged with micro-CT scanning
Al-Garni and Al-Anazi [15] correlated the wettabilitycapillary pressure and initial fluids saturation for SaudiArabia crude oil In their study they correlated irreducibleoil saturation and capillary pressures using rock centrifugemeasurements for Berea rock Sandstone samples on Saudicrude oils during drainage and imbibition cycles by varying
4 Journal of Petroleum Engineering
Figure 7 Saturator
Core
Porous plate
PressuresupplyPressure
regulator
PD
Manometer
Figure 8 Porous plate diagram
each time the wettability of the tested samples using differentSaudi oils (heavy medium and light)
Green et al [16] presented a new method of determiningthe capillary pressure by directmeasurement of the saturationusing magnetic resonance imaging (MRI) He used theHassler and Brunner equation at each radial position inthe rock to calculate the capillary pressure which togetherwith saturation measured with MRI at each position directlyproduces a capillary pressure curve with as few as singlecentrifuge equilibrium [10] The technique is reported to berapid accurate and ideally suited to study ldquotightrdquo or lowpermeability rocks
Chen et al [17] discussed on NMR wettability indiceseffect of OBM on wettability and NMR responses The find-ings of that study were that cationic surfactant dodecylaminealters the wettability of glass slide surface while anionicsurfactant stearic acid alters the wettability ofmarble surfaceThey were able to correlate the proposed NMR wettabilityindices (water index oil index or combined index) with thetraditional Amott-Harvey indices suggesting that quantita-tive information about rock wettability can be gained fromNMRmeasurements
Figure 9 Ceramic platecapillary pressure cell
OrsquoCarroll et al [18] in their study predicted two-phasecapillary pressuresaturation relationships in fractional wet-tability systems They presented a new two-phase capillarypressuresaturation model for application to the predictionof primary drainage and imbibition relations in fractionalwettability media That new model was based on extensionof Leverett scaling theory
Bekri et al [19] studied the effect of wettability on thepetrophysical parameters of vuggy carbonates In their studythey modelled a dual network for dual porosity rocks whichsatisfactorily reproduced the capillary pressure curve theporosity and the permeability determined experimentallyon a double porosity rock They found that the contrastbetween primary and secondary pore space characteristicshas a major effect on both the capillary pressure and therelative permeabilities
Li and Firoozabadi [20] showed that if the wettability ofporous media can be altered from preferential liquid wettingto preferential gas-wetting then gas well deliverability in gascondensate reservoirs can be increased
Hui and Blunt [21] studied the effects of rock wettabilityon the flow of oil water and gas in hydrocarbon reservoirsThey described the three-phase fluid configurations anddisplacement processes in a pore of polygonal cross section
4 Methodology
The present work relies on laboratory experimental resultsobtained from routine and special core analysis In conduct-ing the routine core analysis properties such as porositypermeability and the percentage saturation of the testedsample were determined while only the capillary pressuredata of the tested samples were determined during the specialcore analysis In this section we describe the experimentalprocedures that were used in determining the above rockproperties
41 Routine Core Analysis
411 Porosity In this study the ULTRAPORE-300 as shownin Figure 4 was used to estimate the absolute porosityof the four (04) tested samples The porosity of a rock ismathematically defined as
120601 =pore volumebulk volume
lowast 100 () (8)
Journal of Petroleum Engineering 5
Figure 10 Water-wet samples loaded into ceramic plate
In this study the ULTRAPORE-300 was used to estimatethe absolute porosity of the four (04) tested samples TheULTRAPORE-300 system software (WINPORE) computedthe grain volume pore volume and the grain density ofthe samples The testing procedure used in determining thegrain volume and pore volume is as follows
412 Grain Volume Determination
(i) The samples were dried and weighted after whichthey were loaded one after the other inside a 11210158401015840diameter matrix cup
(ii) The ULTRAPORE-300 system software (WINPORE)was first calibrated to obtain a reference volume forgrain volume measurement
(iii) Nitrogen gas was allowed to flow into the 11210158401015840diameter matrix cup system at a pressure P (psi)
(iv) The system generated a set of corresponding volumeat that pressure P for each sample loaded and used theBoylersquos law equation in computing the samples grainvolume
413 Pore Volume Determination
(i) The pore volume of the samples was determinedsimilarly as the grain volume except that the systemsoftware was calibrated for pore volume instead ofgrain volume
(ii) The samples were then loaded into a rubber bootplaced inside a hydrostatic core holder at an overbur-den pressure of 200 psi where the nitrogen gas wasallowed to flow in the core holder to fill the porespaces of the samples at equilibrium
(iii) The system software (WINPORE) generated then thepore volume of the samples (Figure 5) The graindensity of each sample was computed by the systemsoftware The bulk volume of the samples was com-puted empirically
414 Air Permeability Determination The testing procedureused is as follows
(i) The samples were loaded inside a core holder con-nected to the gas permeameter (Figure 6)
(ii) Nitrogen gas was allowed to flow into the samplesusing a regulator to obtain a laminar flow regimeThelaminagr flow regime was determined using a bubbleflow meter to ascertain that the flow rate does notexceed 1 ccs
(iii) Using the bubble-tool flow meter the flow rate atwhich the gas flow through the samples was deter-mined using the flow rate definition
(iv) The air permeability was then computed from theequation given below
119896 =2000119875
119887lowast 119876 lowast 120583 lowast (119897119860)
(119875 + 119875119887)2
minus 1198752
119887
(9)
where 119875119887is barometric pressure (atm) 120583 is119873
2viscosity (cp)
P is measured pressure (atm) 119897 is sample length (cm) 119876 isflow rate (ccs) and A is sample area (cm2)
415 Percentage Saturation Determination This property isexpressed mathematically by the following relationship
fluid saturation = total volume of fluidpore volume
lowast 100 () (10)
Saturation is a direct measure of the fluid content of theporous rock It therefore directly influences the hydrocarbonstorage capacity of the reservoir
In the pores of oil or gas reservoirs there always remainssome water that was there before the hydrocarbon entrap-ment At any time during the life of an oil or gas reservoirthe following relationship must hold true
119878119900+ 119878119908+ 119878119892= 10
119878119900=
oil volumepore volume
=119881119900
119881119901
119878119908=water volumepore volume
=119881119908
119881119901
119878119892=
gas volumepore volume
=
119881119892
119881119901
(11)
6 Journal of Petroleum Engineering
(a) Weighing saturated water-wet sample before wettability alteration (119878unmod)
(b) Weighing saturated (light oil) after wettability alteration to oil-wet (119878 mod )
Figure 11
Table 1 Routine core analysis results
Core 119871 119863 BV GV GD Porosity 119878119908119894
119878119900119894
119870119886
(cm) (cm) (cc) (cc) (gcc) () () () (md)102 716 386 8416 2572 268 3056 6279 7088 139546 681 383 7859 5251 265 3318 7198 6458 23184 625 378 7023 4902 264 3020 5941 5875 223X 513 388 6090 4641 269 2379 8731 8627 50
Figure 12 Samples loaded into the ceramic plate after wettability alteration to oil-wet
Journal of Petroleum Engineering 7
35
30
25
20
15
10
5
0
Pc
(psi)
Air-oilAir-brine
K = 13929
Swi = 6279Swir = 1913
120601 = 3056Soi = 7088Sor = 2913
20 30 40 50 60 70 80 90 100
Sw ()
Sample 102 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
35
30
25
20
15
10
5
0
Pc
(psia
)Air-oilAir-brine
K = 231mdSwi = 7198Swir = 1593
120601 = 3318Soi = 6458Sor = 2637
10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 546 capillary pressure versus saturationfor both air-brine and air-oil system
(b)
Figure 13 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod Capillary pressure (119875
119888) versus Saturation (119878
119908) curves
It is common for oil or gas saturation to be zero but watersaturation is always greater than zero
The percentage saturation of the tested samples wasmeasured as follow
(i) The dry weight of the samples was recorded(ii) The samples were loaded in the saturator and air was
evacuated from the saturator for 30 minutes usingvacuum pump
(iii) The saturator was filled with the saturating fluid(brine or light oil) at a pressure of 1000 psi for 24hours after which the samples were removed fromthe saturator and their net weight were recorded(Figure 7)
42 Special Core Analysis For the purpose of this work onlythe capillary pressure of the tested samples was determinedfrom the special core analysis The porous plate method wasused for that purpose In doing so a set of capillary pressuredata was acquired under different wettability conditions Thefirst set of capillary pressure data was acquired for water-wetcore sample while the second set of capillary pressure datawas acquired after the wettability of the samples was alteredto oil wet by smearing paint (alkyd resins) on the surface ofthe tested samples
421 Capillary Pressure Measurement Using the PorousPlate Method
Testing Procedure The semipermeable porous plate was firstprepared (Figure 8) Plates for oil and brine were separated
The plates were first saturated with distilled water or lightmineral oil and then tested for leaks
Once saturated the plate was not allowed to dry becausefractures will often occur Before use the plate was flushedwith the brine or oil that the samples are saturated withThis was accomplished in the cell by pouring some of theliquid into the cell (Figure 9) Cover the plate with 1210158401015840 ofliquid Close the cell and apply a 35 psi air pressure Pressureis generally provided by a pressure gauge control panel whichhas gauges ranging in pressure from 1 psi to 50 psi
Once the plate has been prepared and the samplessaturated they are now loaded into the cell Place a discof white clean tissue paper on one end face of the sampleto prevent possible contamination and damage to thewettability characteristics of the samples The disc shouldbe of the same diameter as the core sample The tissue willensure that good capillary contact is made Once the samplesare in place in the cell (Figure 10) clean the o-rings on thetop and bottom of the barrel Carefully lower the barrel onthe porous plate and samples and align it to the base Gentlyplace the lid on the barrel insert the screw that holds it inplace and do not overtighten
Connect the air pressure source to the valve on the lidPreset the regulator and gauge to the first pressure (1 psi)gently open the valve leading from the pressure panel andlisten for the sound of air flowing into the cell Close theexhaust valve Put the drain line into a small beaker partiallyfilled with water and open the valve in the base of the cellThe pressures used routinely in air-brine system are 1 2 58 15 and 35 psi Pressure is maintained until equilibrium isreached This is determined by weighing the samples on suc-cessive days until the weights of all the samples are constant
8 Journal of Petroleum Engineering
K = 223mdSwi = 5941Swir = 1317
120601 = 3020Soi = 5875Sor = 2472
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
0 10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 84 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
K = 50mdSwi = 8731Swir = 2079
120601 = 2379Soi = 8627Sor = 3400
Sample X capillary pressure versus saturation
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
20 30 40 50 60 70 80 90 100
Sw ()
for both air-brine and air-oil system
(b)
Figure 14 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod
Table 2 Air-brine capillary pressures and saturations of the samples(119878unmod)
119875119888(psi) 119878
119882() 119878
119882() 119878
119882() 119878
119882()
Sample 102 Sample 546 Sample 84 Sample X1 9839 9824 9825 99052 9090 9185 9119 91945 8006 8002 8206 82618 6272 6319 6571 671915 4322 4177 4254 487735 1913 1593 1317 2079
Table 3 Air-oil capillary pressures and saturations of the samples(119878 mod )
119875119888(psi) 119878
119900() 119878
119900() 119878
119900() 119878
119900()
Sample 102 Sample 546 Sample 84 Sample X1 9890 9822 9856 1002 9616 9365 9494 98405 9051 8557 8676 90648 8124 7185 7095 813615 6045 5024 5161 627235 2913 2637 2472 3400
To open the cell close the drain valve and the pressurevalve Slowly open the exhaust valve and once the pressure hasbeen vented the cell can be safely openedThe test is completeonce the weights have been obtained at equilibrium for thelast pressure setting After the test is complete the porousplate must be cleaned and prepared for storage or reuse
The testing procedure described above was used for air-brine system whereby the wettability of the core sample wasnot altered (water wet samples) Air-oil tests are performedin the same manner as described above except that a low
viscosity refined mineral oil such as Isopar was used tosaturate the samples and the porous plate Because air-brineand air-oil systems have different surface tension values thepressure settings were different and 05 1 2 5 8 and 15 psiwere used for air-oil system
422 Air-Brine System Capillary Pressure Measurement Inthis study the procedure described above was used for air-brine system in acquiring the capillary pressure data of thecore samples
423 Air-Oil System Capillary Pressure Measurement Air-oil tests are performed in the same manner as for the air-brine system except that the samples and the porous platewere saturated with oil and the pressure settings are 05 12 5 8 and 12 psi In this work the air-oil system procedureof measuring capillary pressure was as for the air-brineexcept that the wettability of the core samples was altered tooil-wet
424 Wettability Modification Glycerophtalic paint (Sigma-Aldrich Inc) was dissolved by stirring overnight in acetoneat room temperature Then the solution was placed in a60 cm3 syringe with a 20-gauge blunt tip needle The tip-to-substrate distance was set at 20 cm and the solution wasflowed on the surface of the samples at a rate of 15mLhrwith a syringe pump (KDS100 KD Scientific Inc) as shownin Figures 11(a) and 11(b) The paint solutions used forwettabilitymodification in the experimental work were 2mmthick Samples were then loaded into the ceramic plate afterwettability alteration (Figure 12) Samples whose surfaces
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
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![Page 3: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/3.jpg)
Journal of Petroleum Engineering 3
Figure 4 ULTRAPORE-300 assembly
contact angle Capillary pressure data are not only importantfor obtaining reservoir rock properties such as pore sizedistribution permeability andwater saturation profile withinthe oil reservoir but also provide important information forwater flooding designs and reservoir simulation studies
Capillary pressure is typically measured in the laboratoryby mercury injection porous plate or centrifugation tech-niquesThe porous platemethod (PP) has been used for yearsin acquiring reliable capillary pressure data representative ofreservoir rock fluid properties In recent years the methodis also found to be reliable and subject to less experimentalerrors and analysis when used for electrical resistivity (RI)measurements as well A major problem has been the longtime scales required for achieving reliable data
The mercury injection technique is fast and can reachvery high capillary pressure but the test uses nonrepresenta-tive fluid mercury and it is destructive whereas the centrifu-gation technique [10] uses reservoir fluids and decreases theequilibrium time by using high centrifugal forces
In this study the porous plate method was used inacquiring the capillary pressure data of the tested samples
The term relative permeability refers to the phase perme-ability relative to the absolute permeability k
119896119903119900=119896119900
119896 119896
119903119908=119896119908
119896 119896
119903119892=
119896119892
119896 (6)
Several mathematical models have been proposed to inferrelative permeability from capillary pressure data In 2008Derahman andZahoor demonstrated amethodof calculatingthe permeability using capillary pressure curves measuredby mercury injection [7] A tortuosity factor in the modelwas earlier introduced and the method was modified byrepresenting capillary pressure curve as a power law functionof the wetting phase saturation [11ndash13] As mentioned pre-viously capillary pressure and relative permeability are bothmeasured in the laboratory however it is time consumingand expensive to both in many cases For the purpose of thisstudy the empirical Brooks-Corey-Burdine formulae [11ndash13]are used
119896119903119908= 1199044
119890119908
119896119903119899119908
= (1 minus 119904119890119908)2
(1 minus 1199042
119890119908)
119904119890119908=119904119908minus 119904119903119908
1 minus 119904119903119908
(7)
Figure 5 WINPORE snapshot
Figure 6 Frank Jones liquid permeameter
where 119870119903119908
and 119870119903119899119908
are the wetting phase and nonwettingphase relative permeability respectively 119878
119890119908 119878119903119908 and 119878
119908are
the effective wetting phase saturation wetting phase residualsaturation and wetting phase saturation respectively
2 Justification for This Study
Several studies have been conducted on wettability reversaleffects on oil recovery using different surfactants to deliber-ately improve oil recovery however the literature is sparseon wettability alteration that results from contact with thecomponents of corrosion inhibitors or paints the focus of thisstudy Moreover no study of such has been reported on theNiger Delta formations
3 Brief Literature Cited
Sayari and Blunt [14] performed benchmark experimentson multiphase flow in which they investigated the effectof wettability on relative permeability capillary pressureelectrical resistivity and nuclear magnetic resonance (NMR)In that study they compared the results obtained from a suiteof experimental measurements on well characterized systemsthat studies relevant properties such as capillary pressurerelative permeability NMR response and resistivity indexwith numerical predictions using pore-scale modeling wherethe pore space was imaged with micro-CT scanning
Al-Garni and Al-Anazi [15] correlated the wettabilitycapillary pressure and initial fluids saturation for SaudiArabia crude oil In their study they correlated irreducibleoil saturation and capillary pressures using rock centrifugemeasurements for Berea rock Sandstone samples on Saudicrude oils during drainage and imbibition cycles by varying
4 Journal of Petroleum Engineering
Figure 7 Saturator
Core
Porous plate
PressuresupplyPressure
regulator
PD
Manometer
Figure 8 Porous plate diagram
each time the wettability of the tested samples using differentSaudi oils (heavy medium and light)
Green et al [16] presented a new method of determiningthe capillary pressure by directmeasurement of the saturationusing magnetic resonance imaging (MRI) He used theHassler and Brunner equation at each radial position inthe rock to calculate the capillary pressure which togetherwith saturation measured with MRI at each position directlyproduces a capillary pressure curve with as few as singlecentrifuge equilibrium [10] The technique is reported to berapid accurate and ideally suited to study ldquotightrdquo or lowpermeability rocks
Chen et al [17] discussed on NMR wettability indiceseffect of OBM on wettability and NMR responses The find-ings of that study were that cationic surfactant dodecylaminealters the wettability of glass slide surface while anionicsurfactant stearic acid alters the wettability ofmarble surfaceThey were able to correlate the proposed NMR wettabilityindices (water index oil index or combined index) with thetraditional Amott-Harvey indices suggesting that quantita-tive information about rock wettability can be gained fromNMRmeasurements
Figure 9 Ceramic platecapillary pressure cell
OrsquoCarroll et al [18] in their study predicted two-phasecapillary pressuresaturation relationships in fractional wet-tability systems They presented a new two-phase capillarypressuresaturation model for application to the predictionof primary drainage and imbibition relations in fractionalwettability media That new model was based on extensionof Leverett scaling theory
Bekri et al [19] studied the effect of wettability on thepetrophysical parameters of vuggy carbonates In their studythey modelled a dual network for dual porosity rocks whichsatisfactorily reproduced the capillary pressure curve theporosity and the permeability determined experimentallyon a double porosity rock They found that the contrastbetween primary and secondary pore space characteristicshas a major effect on both the capillary pressure and therelative permeabilities
Li and Firoozabadi [20] showed that if the wettability ofporous media can be altered from preferential liquid wettingto preferential gas-wetting then gas well deliverability in gascondensate reservoirs can be increased
Hui and Blunt [21] studied the effects of rock wettabilityon the flow of oil water and gas in hydrocarbon reservoirsThey described the three-phase fluid configurations anddisplacement processes in a pore of polygonal cross section
4 Methodology
The present work relies on laboratory experimental resultsobtained from routine and special core analysis In conduct-ing the routine core analysis properties such as porositypermeability and the percentage saturation of the testedsample were determined while only the capillary pressuredata of the tested samples were determined during the specialcore analysis In this section we describe the experimentalprocedures that were used in determining the above rockproperties
41 Routine Core Analysis
411 Porosity In this study the ULTRAPORE-300 as shownin Figure 4 was used to estimate the absolute porosityof the four (04) tested samples The porosity of a rock ismathematically defined as
120601 =pore volumebulk volume
lowast 100 () (8)
Journal of Petroleum Engineering 5
Figure 10 Water-wet samples loaded into ceramic plate
In this study the ULTRAPORE-300 was used to estimatethe absolute porosity of the four (04) tested samples TheULTRAPORE-300 system software (WINPORE) computedthe grain volume pore volume and the grain density ofthe samples The testing procedure used in determining thegrain volume and pore volume is as follows
412 Grain Volume Determination
(i) The samples were dried and weighted after whichthey were loaded one after the other inside a 11210158401015840diameter matrix cup
(ii) The ULTRAPORE-300 system software (WINPORE)was first calibrated to obtain a reference volume forgrain volume measurement
(iii) Nitrogen gas was allowed to flow into the 11210158401015840diameter matrix cup system at a pressure P (psi)
(iv) The system generated a set of corresponding volumeat that pressure P for each sample loaded and used theBoylersquos law equation in computing the samples grainvolume
413 Pore Volume Determination
(i) The pore volume of the samples was determinedsimilarly as the grain volume except that the systemsoftware was calibrated for pore volume instead ofgrain volume
(ii) The samples were then loaded into a rubber bootplaced inside a hydrostatic core holder at an overbur-den pressure of 200 psi where the nitrogen gas wasallowed to flow in the core holder to fill the porespaces of the samples at equilibrium
(iii) The system software (WINPORE) generated then thepore volume of the samples (Figure 5) The graindensity of each sample was computed by the systemsoftware The bulk volume of the samples was com-puted empirically
414 Air Permeability Determination The testing procedureused is as follows
(i) The samples were loaded inside a core holder con-nected to the gas permeameter (Figure 6)
(ii) Nitrogen gas was allowed to flow into the samplesusing a regulator to obtain a laminar flow regimeThelaminagr flow regime was determined using a bubbleflow meter to ascertain that the flow rate does notexceed 1 ccs
(iii) Using the bubble-tool flow meter the flow rate atwhich the gas flow through the samples was deter-mined using the flow rate definition
(iv) The air permeability was then computed from theequation given below
119896 =2000119875
119887lowast 119876 lowast 120583 lowast (119897119860)
(119875 + 119875119887)2
minus 1198752
119887
(9)
where 119875119887is barometric pressure (atm) 120583 is119873
2viscosity (cp)
P is measured pressure (atm) 119897 is sample length (cm) 119876 isflow rate (ccs) and A is sample area (cm2)
415 Percentage Saturation Determination This property isexpressed mathematically by the following relationship
fluid saturation = total volume of fluidpore volume
lowast 100 () (10)
Saturation is a direct measure of the fluid content of theporous rock It therefore directly influences the hydrocarbonstorage capacity of the reservoir
In the pores of oil or gas reservoirs there always remainssome water that was there before the hydrocarbon entrap-ment At any time during the life of an oil or gas reservoirthe following relationship must hold true
119878119900+ 119878119908+ 119878119892= 10
119878119900=
oil volumepore volume
=119881119900
119881119901
119878119908=water volumepore volume
=119881119908
119881119901
119878119892=
gas volumepore volume
=
119881119892
119881119901
(11)
6 Journal of Petroleum Engineering
(a) Weighing saturated water-wet sample before wettability alteration (119878unmod)
(b) Weighing saturated (light oil) after wettability alteration to oil-wet (119878 mod )
Figure 11
Table 1 Routine core analysis results
Core 119871 119863 BV GV GD Porosity 119878119908119894
119878119900119894
119870119886
(cm) (cm) (cc) (cc) (gcc) () () () (md)102 716 386 8416 2572 268 3056 6279 7088 139546 681 383 7859 5251 265 3318 7198 6458 23184 625 378 7023 4902 264 3020 5941 5875 223X 513 388 6090 4641 269 2379 8731 8627 50
Figure 12 Samples loaded into the ceramic plate after wettability alteration to oil-wet
Journal of Petroleum Engineering 7
35
30
25
20
15
10
5
0
Pc
(psi)
Air-oilAir-brine
K = 13929
Swi = 6279Swir = 1913
120601 = 3056Soi = 7088Sor = 2913
20 30 40 50 60 70 80 90 100
Sw ()
Sample 102 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
35
30
25
20
15
10
5
0
Pc
(psia
)Air-oilAir-brine
K = 231mdSwi = 7198Swir = 1593
120601 = 3318Soi = 6458Sor = 2637
10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 546 capillary pressure versus saturationfor both air-brine and air-oil system
(b)
Figure 13 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod Capillary pressure (119875
119888) versus Saturation (119878
119908) curves
It is common for oil or gas saturation to be zero but watersaturation is always greater than zero
The percentage saturation of the tested samples wasmeasured as follow
(i) The dry weight of the samples was recorded(ii) The samples were loaded in the saturator and air was
evacuated from the saturator for 30 minutes usingvacuum pump
(iii) The saturator was filled with the saturating fluid(brine or light oil) at a pressure of 1000 psi for 24hours after which the samples were removed fromthe saturator and their net weight were recorded(Figure 7)
42 Special Core Analysis For the purpose of this work onlythe capillary pressure of the tested samples was determinedfrom the special core analysis The porous plate method wasused for that purpose In doing so a set of capillary pressuredata was acquired under different wettability conditions Thefirst set of capillary pressure data was acquired for water-wetcore sample while the second set of capillary pressure datawas acquired after the wettability of the samples was alteredto oil wet by smearing paint (alkyd resins) on the surface ofthe tested samples
421 Capillary Pressure Measurement Using the PorousPlate Method
Testing Procedure The semipermeable porous plate was firstprepared (Figure 8) Plates for oil and brine were separated
The plates were first saturated with distilled water or lightmineral oil and then tested for leaks
Once saturated the plate was not allowed to dry becausefractures will often occur Before use the plate was flushedwith the brine or oil that the samples are saturated withThis was accomplished in the cell by pouring some of theliquid into the cell (Figure 9) Cover the plate with 1210158401015840 ofliquid Close the cell and apply a 35 psi air pressure Pressureis generally provided by a pressure gauge control panel whichhas gauges ranging in pressure from 1 psi to 50 psi
Once the plate has been prepared and the samplessaturated they are now loaded into the cell Place a discof white clean tissue paper on one end face of the sampleto prevent possible contamination and damage to thewettability characteristics of the samples The disc shouldbe of the same diameter as the core sample The tissue willensure that good capillary contact is made Once the samplesare in place in the cell (Figure 10) clean the o-rings on thetop and bottom of the barrel Carefully lower the barrel onthe porous plate and samples and align it to the base Gentlyplace the lid on the barrel insert the screw that holds it inplace and do not overtighten
Connect the air pressure source to the valve on the lidPreset the regulator and gauge to the first pressure (1 psi)gently open the valve leading from the pressure panel andlisten for the sound of air flowing into the cell Close theexhaust valve Put the drain line into a small beaker partiallyfilled with water and open the valve in the base of the cellThe pressures used routinely in air-brine system are 1 2 58 15 and 35 psi Pressure is maintained until equilibrium isreached This is determined by weighing the samples on suc-cessive days until the weights of all the samples are constant
8 Journal of Petroleum Engineering
K = 223mdSwi = 5941Swir = 1317
120601 = 3020Soi = 5875Sor = 2472
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
0 10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 84 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
K = 50mdSwi = 8731Swir = 2079
120601 = 2379Soi = 8627Sor = 3400
Sample X capillary pressure versus saturation
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
20 30 40 50 60 70 80 90 100
Sw ()
for both air-brine and air-oil system
(b)
Figure 14 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod
Table 2 Air-brine capillary pressures and saturations of the samples(119878unmod)
119875119888(psi) 119878
119882() 119878
119882() 119878
119882() 119878
119882()
Sample 102 Sample 546 Sample 84 Sample X1 9839 9824 9825 99052 9090 9185 9119 91945 8006 8002 8206 82618 6272 6319 6571 671915 4322 4177 4254 487735 1913 1593 1317 2079
Table 3 Air-oil capillary pressures and saturations of the samples(119878 mod )
119875119888(psi) 119878
119900() 119878
119900() 119878
119900() 119878
119900()
Sample 102 Sample 546 Sample 84 Sample X1 9890 9822 9856 1002 9616 9365 9494 98405 9051 8557 8676 90648 8124 7185 7095 813615 6045 5024 5161 627235 2913 2637 2472 3400
To open the cell close the drain valve and the pressurevalve Slowly open the exhaust valve and once the pressure hasbeen vented the cell can be safely openedThe test is completeonce the weights have been obtained at equilibrium for thelast pressure setting After the test is complete the porousplate must be cleaned and prepared for storage or reuse
The testing procedure described above was used for air-brine system whereby the wettability of the core sample wasnot altered (water wet samples) Air-oil tests are performedin the same manner as described above except that a low
viscosity refined mineral oil such as Isopar was used tosaturate the samples and the porous plate Because air-brineand air-oil systems have different surface tension values thepressure settings were different and 05 1 2 5 8 and 15 psiwere used for air-oil system
422 Air-Brine System Capillary Pressure Measurement Inthis study the procedure described above was used for air-brine system in acquiring the capillary pressure data of thecore samples
423 Air-Oil System Capillary Pressure Measurement Air-oil tests are performed in the same manner as for the air-brine system except that the samples and the porous platewere saturated with oil and the pressure settings are 05 12 5 8 and 12 psi In this work the air-oil system procedureof measuring capillary pressure was as for the air-brineexcept that the wettability of the core samples was altered tooil-wet
424 Wettability Modification Glycerophtalic paint (Sigma-Aldrich Inc) was dissolved by stirring overnight in acetoneat room temperature Then the solution was placed in a60 cm3 syringe with a 20-gauge blunt tip needle The tip-to-substrate distance was set at 20 cm and the solution wasflowed on the surface of the samples at a rate of 15mLhrwith a syringe pump (KDS100 KD Scientific Inc) as shownin Figures 11(a) and 11(b) The paint solutions used forwettabilitymodification in the experimental work were 2mmthick Samples were then loaded into the ceramic plate afterwettability alteration (Figure 12) Samples whose surfaces
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
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![Page 4: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/4.jpg)
4 Journal of Petroleum Engineering
Figure 7 Saturator
Core
Porous plate
PressuresupplyPressure
regulator
PD
Manometer
Figure 8 Porous plate diagram
each time the wettability of the tested samples using differentSaudi oils (heavy medium and light)
Green et al [16] presented a new method of determiningthe capillary pressure by directmeasurement of the saturationusing magnetic resonance imaging (MRI) He used theHassler and Brunner equation at each radial position inthe rock to calculate the capillary pressure which togetherwith saturation measured with MRI at each position directlyproduces a capillary pressure curve with as few as singlecentrifuge equilibrium [10] The technique is reported to berapid accurate and ideally suited to study ldquotightrdquo or lowpermeability rocks
Chen et al [17] discussed on NMR wettability indiceseffect of OBM on wettability and NMR responses The find-ings of that study were that cationic surfactant dodecylaminealters the wettability of glass slide surface while anionicsurfactant stearic acid alters the wettability ofmarble surfaceThey were able to correlate the proposed NMR wettabilityindices (water index oil index or combined index) with thetraditional Amott-Harvey indices suggesting that quantita-tive information about rock wettability can be gained fromNMRmeasurements
Figure 9 Ceramic platecapillary pressure cell
OrsquoCarroll et al [18] in their study predicted two-phasecapillary pressuresaturation relationships in fractional wet-tability systems They presented a new two-phase capillarypressuresaturation model for application to the predictionof primary drainage and imbibition relations in fractionalwettability media That new model was based on extensionof Leverett scaling theory
Bekri et al [19] studied the effect of wettability on thepetrophysical parameters of vuggy carbonates In their studythey modelled a dual network for dual porosity rocks whichsatisfactorily reproduced the capillary pressure curve theporosity and the permeability determined experimentallyon a double porosity rock They found that the contrastbetween primary and secondary pore space characteristicshas a major effect on both the capillary pressure and therelative permeabilities
Li and Firoozabadi [20] showed that if the wettability ofporous media can be altered from preferential liquid wettingto preferential gas-wetting then gas well deliverability in gascondensate reservoirs can be increased
Hui and Blunt [21] studied the effects of rock wettabilityon the flow of oil water and gas in hydrocarbon reservoirsThey described the three-phase fluid configurations anddisplacement processes in a pore of polygonal cross section
4 Methodology
The present work relies on laboratory experimental resultsobtained from routine and special core analysis In conduct-ing the routine core analysis properties such as porositypermeability and the percentage saturation of the testedsample were determined while only the capillary pressuredata of the tested samples were determined during the specialcore analysis In this section we describe the experimentalprocedures that were used in determining the above rockproperties
41 Routine Core Analysis
411 Porosity In this study the ULTRAPORE-300 as shownin Figure 4 was used to estimate the absolute porosityof the four (04) tested samples The porosity of a rock ismathematically defined as
120601 =pore volumebulk volume
lowast 100 () (8)
Journal of Petroleum Engineering 5
Figure 10 Water-wet samples loaded into ceramic plate
In this study the ULTRAPORE-300 was used to estimatethe absolute porosity of the four (04) tested samples TheULTRAPORE-300 system software (WINPORE) computedthe grain volume pore volume and the grain density ofthe samples The testing procedure used in determining thegrain volume and pore volume is as follows
412 Grain Volume Determination
(i) The samples were dried and weighted after whichthey were loaded one after the other inside a 11210158401015840diameter matrix cup
(ii) The ULTRAPORE-300 system software (WINPORE)was first calibrated to obtain a reference volume forgrain volume measurement
(iii) Nitrogen gas was allowed to flow into the 11210158401015840diameter matrix cup system at a pressure P (psi)
(iv) The system generated a set of corresponding volumeat that pressure P for each sample loaded and used theBoylersquos law equation in computing the samples grainvolume
413 Pore Volume Determination
(i) The pore volume of the samples was determinedsimilarly as the grain volume except that the systemsoftware was calibrated for pore volume instead ofgrain volume
(ii) The samples were then loaded into a rubber bootplaced inside a hydrostatic core holder at an overbur-den pressure of 200 psi where the nitrogen gas wasallowed to flow in the core holder to fill the porespaces of the samples at equilibrium
(iii) The system software (WINPORE) generated then thepore volume of the samples (Figure 5) The graindensity of each sample was computed by the systemsoftware The bulk volume of the samples was com-puted empirically
414 Air Permeability Determination The testing procedureused is as follows
(i) The samples were loaded inside a core holder con-nected to the gas permeameter (Figure 6)
(ii) Nitrogen gas was allowed to flow into the samplesusing a regulator to obtain a laminar flow regimeThelaminagr flow regime was determined using a bubbleflow meter to ascertain that the flow rate does notexceed 1 ccs
(iii) Using the bubble-tool flow meter the flow rate atwhich the gas flow through the samples was deter-mined using the flow rate definition
(iv) The air permeability was then computed from theequation given below
119896 =2000119875
119887lowast 119876 lowast 120583 lowast (119897119860)
(119875 + 119875119887)2
minus 1198752
119887
(9)
where 119875119887is barometric pressure (atm) 120583 is119873
2viscosity (cp)
P is measured pressure (atm) 119897 is sample length (cm) 119876 isflow rate (ccs) and A is sample area (cm2)
415 Percentage Saturation Determination This property isexpressed mathematically by the following relationship
fluid saturation = total volume of fluidpore volume
lowast 100 () (10)
Saturation is a direct measure of the fluid content of theporous rock It therefore directly influences the hydrocarbonstorage capacity of the reservoir
In the pores of oil or gas reservoirs there always remainssome water that was there before the hydrocarbon entrap-ment At any time during the life of an oil or gas reservoirthe following relationship must hold true
119878119900+ 119878119908+ 119878119892= 10
119878119900=
oil volumepore volume
=119881119900
119881119901
119878119908=water volumepore volume
=119881119908
119881119901
119878119892=
gas volumepore volume
=
119881119892
119881119901
(11)
6 Journal of Petroleum Engineering
(a) Weighing saturated water-wet sample before wettability alteration (119878unmod)
(b) Weighing saturated (light oil) after wettability alteration to oil-wet (119878 mod )
Figure 11
Table 1 Routine core analysis results
Core 119871 119863 BV GV GD Porosity 119878119908119894
119878119900119894
119870119886
(cm) (cm) (cc) (cc) (gcc) () () () (md)102 716 386 8416 2572 268 3056 6279 7088 139546 681 383 7859 5251 265 3318 7198 6458 23184 625 378 7023 4902 264 3020 5941 5875 223X 513 388 6090 4641 269 2379 8731 8627 50
Figure 12 Samples loaded into the ceramic plate after wettability alteration to oil-wet
Journal of Petroleum Engineering 7
35
30
25
20
15
10
5
0
Pc
(psi)
Air-oilAir-brine
K = 13929
Swi = 6279Swir = 1913
120601 = 3056Soi = 7088Sor = 2913
20 30 40 50 60 70 80 90 100
Sw ()
Sample 102 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
35
30
25
20
15
10
5
0
Pc
(psia
)Air-oilAir-brine
K = 231mdSwi = 7198Swir = 1593
120601 = 3318Soi = 6458Sor = 2637
10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 546 capillary pressure versus saturationfor both air-brine and air-oil system
(b)
Figure 13 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod Capillary pressure (119875
119888) versus Saturation (119878
119908) curves
It is common for oil or gas saturation to be zero but watersaturation is always greater than zero
The percentage saturation of the tested samples wasmeasured as follow
(i) The dry weight of the samples was recorded(ii) The samples were loaded in the saturator and air was
evacuated from the saturator for 30 minutes usingvacuum pump
(iii) The saturator was filled with the saturating fluid(brine or light oil) at a pressure of 1000 psi for 24hours after which the samples were removed fromthe saturator and their net weight were recorded(Figure 7)
42 Special Core Analysis For the purpose of this work onlythe capillary pressure of the tested samples was determinedfrom the special core analysis The porous plate method wasused for that purpose In doing so a set of capillary pressuredata was acquired under different wettability conditions Thefirst set of capillary pressure data was acquired for water-wetcore sample while the second set of capillary pressure datawas acquired after the wettability of the samples was alteredto oil wet by smearing paint (alkyd resins) on the surface ofthe tested samples
421 Capillary Pressure Measurement Using the PorousPlate Method
Testing Procedure The semipermeable porous plate was firstprepared (Figure 8) Plates for oil and brine were separated
The plates were first saturated with distilled water or lightmineral oil and then tested for leaks
Once saturated the plate was not allowed to dry becausefractures will often occur Before use the plate was flushedwith the brine or oil that the samples are saturated withThis was accomplished in the cell by pouring some of theliquid into the cell (Figure 9) Cover the plate with 1210158401015840 ofliquid Close the cell and apply a 35 psi air pressure Pressureis generally provided by a pressure gauge control panel whichhas gauges ranging in pressure from 1 psi to 50 psi
Once the plate has been prepared and the samplessaturated they are now loaded into the cell Place a discof white clean tissue paper on one end face of the sampleto prevent possible contamination and damage to thewettability characteristics of the samples The disc shouldbe of the same diameter as the core sample The tissue willensure that good capillary contact is made Once the samplesare in place in the cell (Figure 10) clean the o-rings on thetop and bottom of the barrel Carefully lower the barrel onthe porous plate and samples and align it to the base Gentlyplace the lid on the barrel insert the screw that holds it inplace and do not overtighten
Connect the air pressure source to the valve on the lidPreset the regulator and gauge to the first pressure (1 psi)gently open the valve leading from the pressure panel andlisten for the sound of air flowing into the cell Close theexhaust valve Put the drain line into a small beaker partiallyfilled with water and open the valve in the base of the cellThe pressures used routinely in air-brine system are 1 2 58 15 and 35 psi Pressure is maintained until equilibrium isreached This is determined by weighing the samples on suc-cessive days until the weights of all the samples are constant
8 Journal of Petroleum Engineering
K = 223mdSwi = 5941Swir = 1317
120601 = 3020Soi = 5875Sor = 2472
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
0 10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 84 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
K = 50mdSwi = 8731Swir = 2079
120601 = 2379Soi = 8627Sor = 3400
Sample X capillary pressure versus saturation
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
20 30 40 50 60 70 80 90 100
Sw ()
for both air-brine and air-oil system
(b)
Figure 14 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod
Table 2 Air-brine capillary pressures and saturations of the samples(119878unmod)
119875119888(psi) 119878
119882() 119878
119882() 119878
119882() 119878
119882()
Sample 102 Sample 546 Sample 84 Sample X1 9839 9824 9825 99052 9090 9185 9119 91945 8006 8002 8206 82618 6272 6319 6571 671915 4322 4177 4254 487735 1913 1593 1317 2079
Table 3 Air-oil capillary pressures and saturations of the samples(119878 mod )
119875119888(psi) 119878
119900() 119878
119900() 119878
119900() 119878
119900()
Sample 102 Sample 546 Sample 84 Sample X1 9890 9822 9856 1002 9616 9365 9494 98405 9051 8557 8676 90648 8124 7185 7095 813615 6045 5024 5161 627235 2913 2637 2472 3400
To open the cell close the drain valve and the pressurevalve Slowly open the exhaust valve and once the pressure hasbeen vented the cell can be safely openedThe test is completeonce the weights have been obtained at equilibrium for thelast pressure setting After the test is complete the porousplate must be cleaned and prepared for storage or reuse
The testing procedure described above was used for air-brine system whereby the wettability of the core sample wasnot altered (water wet samples) Air-oil tests are performedin the same manner as described above except that a low
viscosity refined mineral oil such as Isopar was used tosaturate the samples and the porous plate Because air-brineand air-oil systems have different surface tension values thepressure settings were different and 05 1 2 5 8 and 15 psiwere used for air-oil system
422 Air-Brine System Capillary Pressure Measurement Inthis study the procedure described above was used for air-brine system in acquiring the capillary pressure data of thecore samples
423 Air-Oil System Capillary Pressure Measurement Air-oil tests are performed in the same manner as for the air-brine system except that the samples and the porous platewere saturated with oil and the pressure settings are 05 12 5 8 and 12 psi In this work the air-oil system procedureof measuring capillary pressure was as for the air-brineexcept that the wettability of the core samples was altered tooil-wet
424 Wettability Modification Glycerophtalic paint (Sigma-Aldrich Inc) was dissolved by stirring overnight in acetoneat room temperature Then the solution was placed in a60 cm3 syringe with a 20-gauge blunt tip needle The tip-to-substrate distance was set at 20 cm and the solution wasflowed on the surface of the samples at a rate of 15mLhrwith a syringe pump (KDS100 KD Scientific Inc) as shownin Figures 11(a) and 11(b) The paint solutions used forwettabilitymodification in the experimental work were 2mmthick Samples were then loaded into the ceramic plate afterwettability alteration (Figure 12) Samples whose surfaces
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
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![Page 5: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/5.jpg)
Journal of Petroleum Engineering 5
Figure 10 Water-wet samples loaded into ceramic plate
In this study the ULTRAPORE-300 was used to estimatethe absolute porosity of the four (04) tested samples TheULTRAPORE-300 system software (WINPORE) computedthe grain volume pore volume and the grain density ofthe samples The testing procedure used in determining thegrain volume and pore volume is as follows
412 Grain Volume Determination
(i) The samples were dried and weighted after whichthey were loaded one after the other inside a 11210158401015840diameter matrix cup
(ii) The ULTRAPORE-300 system software (WINPORE)was first calibrated to obtain a reference volume forgrain volume measurement
(iii) Nitrogen gas was allowed to flow into the 11210158401015840diameter matrix cup system at a pressure P (psi)
(iv) The system generated a set of corresponding volumeat that pressure P for each sample loaded and used theBoylersquos law equation in computing the samples grainvolume
413 Pore Volume Determination
(i) The pore volume of the samples was determinedsimilarly as the grain volume except that the systemsoftware was calibrated for pore volume instead ofgrain volume
(ii) The samples were then loaded into a rubber bootplaced inside a hydrostatic core holder at an overbur-den pressure of 200 psi where the nitrogen gas wasallowed to flow in the core holder to fill the porespaces of the samples at equilibrium
(iii) The system software (WINPORE) generated then thepore volume of the samples (Figure 5) The graindensity of each sample was computed by the systemsoftware The bulk volume of the samples was com-puted empirically
414 Air Permeability Determination The testing procedureused is as follows
(i) The samples were loaded inside a core holder con-nected to the gas permeameter (Figure 6)
(ii) Nitrogen gas was allowed to flow into the samplesusing a regulator to obtain a laminar flow regimeThelaminagr flow regime was determined using a bubbleflow meter to ascertain that the flow rate does notexceed 1 ccs
(iii) Using the bubble-tool flow meter the flow rate atwhich the gas flow through the samples was deter-mined using the flow rate definition
(iv) The air permeability was then computed from theequation given below
119896 =2000119875
119887lowast 119876 lowast 120583 lowast (119897119860)
(119875 + 119875119887)2
minus 1198752
119887
(9)
where 119875119887is barometric pressure (atm) 120583 is119873
2viscosity (cp)
P is measured pressure (atm) 119897 is sample length (cm) 119876 isflow rate (ccs) and A is sample area (cm2)
415 Percentage Saturation Determination This property isexpressed mathematically by the following relationship
fluid saturation = total volume of fluidpore volume
lowast 100 () (10)
Saturation is a direct measure of the fluid content of theporous rock It therefore directly influences the hydrocarbonstorage capacity of the reservoir
In the pores of oil or gas reservoirs there always remainssome water that was there before the hydrocarbon entrap-ment At any time during the life of an oil or gas reservoirthe following relationship must hold true
119878119900+ 119878119908+ 119878119892= 10
119878119900=
oil volumepore volume
=119881119900
119881119901
119878119908=water volumepore volume
=119881119908
119881119901
119878119892=
gas volumepore volume
=
119881119892
119881119901
(11)
6 Journal of Petroleum Engineering
(a) Weighing saturated water-wet sample before wettability alteration (119878unmod)
(b) Weighing saturated (light oil) after wettability alteration to oil-wet (119878 mod )
Figure 11
Table 1 Routine core analysis results
Core 119871 119863 BV GV GD Porosity 119878119908119894
119878119900119894
119870119886
(cm) (cm) (cc) (cc) (gcc) () () () (md)102 716 386 8416 2572 268 3056 6279 7088 139546 681 383 7859 5251 265 3318 7198 6458 23184 625 378 7023 4902 264 3020 5941 5875 223X 513 388 6090 4641 269 2379 8731 8627 50
Figure 12 Samples loaded into the ceramic plate after wettability alteration to oil-wet
Journal of Petroleum Engineering 7
35
30
25
20
15
10
5
0
Pc
(psi)
Air-oilAir-brine
K = 13929
Swi = 6279Swir = 1913
120601 = 3056Soi = 7088Sor = 2913
20 30 40 50 60 70 80 90 100
Sw ()
Sample 102 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
35
30
25
20
15
10
5
0
Pc
(psia
)Air-oilAir-brine
K = 231mdSwi = 7198Swir = 1593
120601 = 3318Soi = 6458Sor = 2637
10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 546 capillary pressure versus saturationfor both air-brine and air-oil system
(b)
Figure 13 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod Capillary pressure (119875
119888) versus Saturation (119878
119908) curves
It is common for oil or gas saturation to be zero but watersaturation is always greater than zero
The percentage saturation of the tested samples wasmeasured as follow
(i) The dry weight of the samples was recorded(ii) The samples were loaded in the saturator and air was
evacuated from the saturator for 30 minutes usingvacuum pump
(iii) The saturator was filled with the saturating fluid(brine or light oil) at a pressure of 1000 psi for 24hours after which the samples were removed fromthe saturator and their net weight were recorded(Figure 7)
42 Special Core Analysis For the purpose of this work onlythe capillary pressure of the tested samples was determinedfrom the special core analysis The porous plate method wasused for that purpose In doing so a set of capillary pressuredata was acquired under different wettability conditions Thefirst set of capillary pressure data was acquired for water-wetcore sample while the second set of capillary pressure datawas acquired after the wettability of the samples was alteredto oil wet by smearing paint (alkyd resins) on the surface ofthe tested samples
421 Capillary Pressure Measurement Using the PorousPlate Method
Testing Procedure The semipermeable porous plate was firstprepared (Figure 8) Plates for oil and brine were separated
The plates were first saturated with distilled water or lightmineral oil and then tested for leaks
Once saturated the plate was not allowed to dry becausefractures will often occur Before use the plate was flushedwith the brine or oil that the samples are saturated withThis was accomplished in the cell by pouring some of theliquid into the cell (Figure 9) Cover the plate with 1210158401015840 ofliquid Close the cell and apply a 35 psi air pressure Pressureis generally provided by a pressure gauge control panel whichhas gauges ranging in pressure from 1 psi to 50 psi
Once the plate has been prepared and the samplessaturated they are now loaded into the cell Place a discof white clean tissue paper on one end face of the sampleto prevent possible contamination and damage to thewettability characteristics of the samples The disc shouldbe of the same diameter as the core sample The tissue willensure that good capillary contact is made Once the samplesare in place in the cell (Figure 10) clean the o-rings on thetop and bottom of the barrel Carefully lower the barrel onthe porous plate and samples and align it to the base Gentlyplace the lid on the barrel insert the screw that holds it inplace and do not overtighten
Connect the air pressure source to the valve on the lidPreset the regulator and gauge to the first pressure (1 psi)gently open the valve leading from the pressure panel andlisten for the sound of air flowing into the cell Close theexhaust valve Put the drain line into a small beaker partiallyfilled with water and open the valve in the base of the cellThe pressures used routinely in air-brine system are 1 2 58 15 and 35 psi Pressure is maintained until equilibrium isreached This is determined by weighing the samples on suc-cessive days until the weights of all the samples are constant
8 Journal of Petroleum Engineering
K = 223mdSwi = 5941Swir = 1317
120601 = 3020Soi = 5875Sor = 2472
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
0 10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 84 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
K = 50mdSwi = 8731Swir = 2079
120601 = 2379Soi = 8627Sor = 3400
Sample X capillary pressure versus saturation
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
20 30 40 50 60 70 80 90 100
Sw ()
for both air-brine and air-oil system
(b)
Figure 14 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod
Table 2 Air-brine capillary pressures and saturations of the samples(119878unmod)
119875119888(psi) 119878
119882() 119878
119882() 119878
119882() 119878
119882()
Sample 102 Sample 546 Sample 84 Sample X1 9839 9824 9825 99052 9090 9185 9119 91945 8006 8002 8206 82618 6272 6319 6571 671915 4322 4177 4254 487735 1913 1593 1317 2079
Table 3 Air-oil capillary pressures and saturations of the samples(119878 mod )
119875119888(psi) 119878
119900() 119878
119900() 119878
119900() 119878
119900()
Sample 102 Sample 546 Sample 84 Sample X1 9890 9822 9856 1002 9616 9365 9494 98405 9051 8557 8676 90648 8124 7185 7095 813615 6045 5024 5161 627235 2913 2637 2472 3400
To open the cell close the drain valve and the pressurevalve Slowly open the exhaust valve and once the pressure hasbeen vented the cell can be safely openedThe test is completeonce the weights have been obtained at equilibrium for thelast pressure setting After the test is complete the porousplate must be cleaned and prepared for storage or reuse
The testing procedure described above was used for air-brine system whereby the wettability of the core sample wasnot altered (water wet samples) Air-oil tests are performedin the same manner as described above except that a low
viscosity refined mineral oil such as Isopar was used tosaturate the samples and the porous plate Because air-brineand air-oil systems have different surface tension values thepressure settings were different and 05 1 2 5 8 and 15 psiwere used for air-oil system
422 Air-Brine System Capillary Pressure Measurement Inthis study the procedure described above was used for air-brine system in acquiring the capillary pressure data of thecore samples
423 Air-Oil System Capillary Pressure Measurement Air-oil tests are performed in the same manner as for the air-brine system except that the samples and the porous platewere saturated with oil and the pressure settings are 05 12 5 8 and 12 psi In this work the air-oil system procedureof measuring capillary pressure was as for the air-brineexcept that the wettability of the core samples was altered tooil-wet
424 Wettability Modification Glycerophtalic paint (Sigma-Aldrich Inc) was dissolved by stirring overnight in acetoneat room temperature Then the solution was placed in a60 cm3 syringe with a 20-gauge blunt tip needle The tip-to-substrate distance was set at 20 cm and the solution wasflowed on the surface of the samples at a rate of 15mLhrwith a syringe pump (KDS100 KD Scientific Inc) as shownin Figures 11(a) and 11(b) The paint solutions used forwettabilitymodification in the experimental work were 2mmthick Samples were then loaded into the ceramic plate afterwettability alteration (Figure 12) Samples whose surfaces
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
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![Page 6: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/6.jpg)
6 Journal of Petroleum Engineering
(a) Weighing saturated water-wet sample before wettability alteration (119878unmod)
(b) Weighing saturated (light oil) after wettability alteration to oil-wet (119878 mod )
Figure 11
Table 1 Routine core analysis results
Core 119871 119863 BV GV GD Porosity 119878119908119894
119878119900119894
119870119886
(cm) (cm) (cc) (cc) (gcc) () () () (md)102 716 386 8416 2572 268 3056 6279 7088 139546 681 383 7859 5251 265 3318 7198 6458 23184 625 378 7023 4902 264 3020 5941 5875 223X 513 388 6090 4641 269 2379 8731 8627 50
Figure 12 Samples loaded into the ceramic plate after wettability alteration to oil-wet
Journal of Petroleum Engineering 7
35
30
25
20
15
10
5
0
Pc
(psi)
Air-oilAir-brine
K = 13929
Swi = 6279Swir = 1913
120601 = 3056Soi = 7088Sor = 2913
20 30 40 50 60 70 80 90 100
Sw ()
Sample 102 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
35
30
25
20
15
10
5
0
Pc
(psia
)Air-oilAir-brine
K = 231mdSwi = 7198Swir = 1593
120601 = 3318Soi = 6458Sor = 2637
10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 546 capillary pressure versus saturationfor both air-brine and air-oil system
(b)
Figure 13 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod Capillary pressure (119875
119888) versus Saturation (119878
119908) curves
It is common for oil or gas saturation to be zero but watersaturation is always greater than zero
The percentage saturation of the tested samples wasmeasured as follow
(i) The dry weight of the samples was recorded(ii) The samples were loaded in the saturator and air was
evacuated from the saturator for 30 minutes usingvacuum pump
(iii) The saturator was filled with the saturating fluid(brine or light oil) at a pressure of 1000 psi for 24hours after which the samples were removed fromthe saturator and their net weight were recorded(Figure 7)
42 Special Core Analysis For the purpose of this work onlythe capillary pressure of the tested samples was determinedfrom the special core analysis The porous plate method wasused for that purpose In doing so a set of capillary pressuredata was acquired under different wettability conditions Thefirst set of capillary pressure data was acquired for water-wetcore sample while the second set of capillary pressure datawas acquired after the wettability of the samples was alteredto oil wet by smearing paint (alkyd resins) on the surface ofthe tested samples
421 Capillary Pressure Measurement Using the PorousPlate Method
Testing Procedure The semipermeable porous plate was firstprepared (Figure 8) Plates for oil and brine were separated
The plates were first saturated with distilled water or lightmineral oil and then tested for leaks
Once saturated the plate was not allowed to dry becausefractures will often occur Before use the plate was flushedwith the brine or oil that the samples are saturated withThis was accomplished in the cell by pouring some of theliquid into the cell (Figure 9) Cover the plate with 1210158401015840 ofliquid Close the cell and apply a 35 psi air pressure Pressureis generally provided by a pressure gauge control panel whichhas gauges ranging in pressure from 1 psi to 50 psi
Once the plate has been prepared and the samplessaturated they are now loaded into the cell Place a discof white clean tissue paper on one end face of the sampleto prevent possible contamination and damage to thewettability characteristics of the samples The disc shouldbe of the same diameter as the core sample The tissue willensure that good capillary contact is made Once the samplesare in place in the cell (Figure 10) clean the o-rings on thetop and bottom of the barrel Carefully lower the barrel onthe porous plate and samples and align it to the base Gentlyplace the lid on the barrel insert the screw that holds it inplace and do not overtighten
Connect the air pressure source to the valve on the lidPreset the regulator and gauge to the first pressure (1 psi)gently open the valve leading from the pressure panel andlisten for the sound of air flowing into the cell Close theexhaust valve Put the drain line into a small beaker partiallyfilled with water and open the valve in the base of the cellThe pressures used routinely in air-brine system are 1 2 58 15 and 35 psi Pressure is maintained until equilibrium isreached This is determined by weighing the samples on suc-cessive days until the weights of all the samples are constant
8 Journal of Petroleum Engineering
K = 223mdSwi = 5941Swir = 1317
120601 = 3020Soi = 5875Sor = 2472
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
0 10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 84 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
K = 50mdSwi = 8731Swir = 2079
120601 = 2379Soi = 8627Sor = 3400
Sample X capillary pressure versus saturation
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
20 30 40 50 60 70 80 90 100
Sw ()
for both air-brine and air-oil system
(b)
Figure 14 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod
Table 2 Air-brine capillary pressures and saturations of the samples(119878unmod)
119875119888(psi) 119878
119882() 119878
119882() 119878
119882() 119878
119882()
Sample 102 Sample 546 Sample 84 Sample X1 9839 9824 9825 99052 9090 9185 9119 91945 8006 8002 8206 82618 6272 6319 6571 671915 4322 4177 4254 487735 1913 1593 1317 2079
Table 3 Air-oil capillary pressures and saturations of the samples(119878 mod )
119875119888(psi) 119878
119900() 119878
119900() 119878
119900() 119878
119900()
Sample 102 Sample 546 Sample 84 Sample X1 9890 9822 9856 1002 9616 9365 9494 98405 9051 8557 8676 90648 8124 7185 7095 813615 6045 5024 5161 627235 2913 2637 2472 3400
To open the cell close the drain valve and the pressurevalve Slowly open the exhaust valve and once the pressure hasbeen vented the cell can be safely openedThe test is completeonce the weights have been obtained at equilibrium for thelast pressure setting After the test is complete the porousplate must be cleaned and prepared for storage or reuse
The testing procedure described above was used for air-brine system whereby the wettability of the core sample wasnot altered (water wet samples) Air-oil tests are performedin the same manner as described above except that a low
viscosity refined mineral oil such as Isopar was used tosaturate the samples and the porous plate Because air-brineand air-oil systems have different surface tension values thepressure settings were different and 05 1 2 5 8 and 15 psiwere used for air-oil system
422 Air-Brine System Capillary Pressure Measurement Inthis study the procedure described above was used for air-brine system in acquiring the capillary pressure data of thecore samples
423 Air-Oil System Capillary Pressure Measurement Air-oil tests are performed in the same manner as for the air-brine system except that the samples and the porous platewere saturated with oil and the pressure settings are 05 12 5 8 and 12 psi In this work the air-oil system procedureof measuring capillary pressure was as for the air-brineexcept that the wettability of the core samples was altered tooil-wet
424 Wettability Modification Glycerophtalic paint (Sigma-Aldrich Inc) was dissolved by stirring overnight in acetoneat room temperature Then the solution was placed in a60 cm3 syringe with a 20-gauge blunt tip needle The tip-to-substrate distance was set at 20 cm and the solution wasflowed on the surface of the samples at a rate of 15mLhrwith a syringe pump (KDS100 KD Scientific Inc) as shownin Figures 11(a) and 11(b) The paint solutions used forwettabilitymodification in the experimental work were 2mmthick Samples were then loaded into the ceramic plate afterwettability alteration (Figure 12) Samples whose surfaces
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
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![Page 7: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/7.jpg)
Journal of Petroleum Engineering 7
35
30
25
20
15
10
5
0
Pc
(psi)
Air-oilAir-brine
K = 13929
Swi = 6279Swir = 1913
120601 = 3056Soi = 7088Sor = 2913
20 30 40 50 60 70 80 90 100
Sw ()
Sample 102 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
35
30
25
20
15
10
5
0
Pc
(psia
)Air-oilAir-brine
K = 231mdSwi = 7198Swir = 1593
120601 = 3318Soi = 6458Sor = 2637
10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 546 capillary pressure versus saturationfor both air-brine and air-oil system
(b)
Figure 13 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod Capillary pressure (119875
119888) versus Saturation (119878
119908) curves
It is common for oil or gas saturation to be zero but watersaturation is always greater than zero
The percentage saturation of the tested samples wasmeasured as follow
(i) The dry weight of the samples was recorded(ii) The samples were loaded in the saturator and air was
evacuated from the saturator for 30 minutes usingvacuum pump
(iii) The saturator was filled with the saturating fluid(brine or light oil) at a pressure of 1000 psi for 24hours after which the samples were removed fromthe saturator and their net weight were recorded(Figure 7)
42 Special Core Analysis For the purpose of this work onlythe capillary pressure of the tested samples was determinedfrom the special core analysis The porous plate method wasused for that purpose In doing so a set of capillary pressuredata was acquired under different wettability conditions Thefirst set of capillary pressure data was acquired for water-wetcore sample while the second set of capillary pressure datawas acquired after the wettability of the samples was alteredto oil wet by smearing paint (alkyd resins) on the surface ofthe tested samples
421 Capillary Pressure Measurement Using the PorousPlate Method
Testing Procedure The semipermeable porous plate was firstprepared (Figure 8) Plates for oil and brine were separated
The plates were first saturated with distilled water or lightmineral oil and then tested for leaks
Once saturated the plate was not allowed to dry becausefractures will often occur Before use the plate was flushedwith the brine or oil that the samples are saturated withThis was accomplished in the cell by pouring some of theliquid into the cell (Figure 9) Cover the plate with 1210158401015840 ofliquid Close the cell and apply a 35 psi air pressure Pressureis generally provided by a pressure gauge control panel whichhas gauges ranging in pressure from 1 psi to 50 psi
Once the plate has been prepared and the samplessaturated they are now loaded into the cell Place a discof white clean tissue paper on one end face of the sampleto prevent possible contamination and damage to thewettability characteristics of the samples The disc shouldbe of the same diameter as the core sample The tissue willensure that good capillary contact is made Once the samplesare in place in the cell (Figure 10) clean the o-rings on thetop and bottom of the barrel Carefully lower the barrel onthe porous plate and samples and align it to the base Gentlyplace the lid on the barrel insert the screw that holds it inplace and do not overtighten
Connect the air pressure source to the valve on the lidPreset the regulator and gauge to the first pressure (1 psi)gently open the valve leading from the pressure panel andlisten for the sound of air flowing into the cell Close theexhaust valve Put the drain line into a small beaker partiallyfilled with water and open the valve in the base of the cellThe pressures used routinely in air-brine system are 1 2 58 15 and 35 psi Pressure is maintained until equilibrium isreached This is determined by weighing the samples on suc-cessive days until the weights of all the samples are constant
8 Journal of Petroleum Engineering
K = 223mdSwi = 5941Swir = 1317
120601 = 3020Soi = 5875Sor = 2472
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
0 10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 84 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
K = 50mdSwi = 8731Swir = 2079
120601 = 2379Soi = 8627Sor = 3400
Sample X capillary pressure versus saturation
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
20 30 40 50 60 70 80 90 100
Sw ()
for both air-brine and air-oil system
(b)
Figure 14 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod
Table 2 Air-brine capillary pressures and saturations of the samples(119878unmod)
119875119888(psi) 119878
119882() 119878
119882() 119878
119882() 119878
119882()
Sample 102 Sample 546 Sample 84 Sample X1 9839 9824 9825 99052 9090 9185 9119 91945 8006 8002 8206 82618 6272 6319 6571 671915 4322 4177 4254 487735 1913 1593 1317 2079
Table 3 Air-oil capillary pressures and saturations of the samples(119878 mod )
119875119888(psi) 119878
119900() 119878
119900() 119878
119900() 119878
119900()
Sample 102 Sample 546 Sample 84 Sample X1 9890 9822 9856 1002 9616 9365 9494 98405 9051 8557 8676 90648 8124 7185 7095 813615 6045 5024 5161 627235 2913 2637 2472 3400
To open the cell close the drain valve and the pressurevalve Slowly open the exhaust valve and once the pressure hasbeen vented the cell can be safely openedThe test is completeonce the weights have been obtained at equilibrium for thelast pressure setting After the test is complete the porousplate must be cleaned and prepared for storage or reuse
The testing procedure described above was used for air-brine system whereby the wettability of the core sample wasnot altered (water wet samples) Air-oil tests are performedin the same manner as described above except that a low
viscosity refined mineral oil such as Isopar was used tosaturate the samples and the porous plate Because air-brineand air-oil systems have different surface tension values thepressure settings were different and 05 1 2 5 8 and 15 psiwere used for air-oil system
422 Air-Brine System Capillary Pressure Measurement Inthis study the procedure described above was used for air-brine system in acquiring the capillary pressure data of thecore samples
423 Air-Oil System Capillary Pressure Measurement Air-oil tests are performed in the same manner as for the air-brine system except that the samples and the porous platewere saturated with oil and the pressure settings are 05 12 5 8 and 12 psi In this work the air-oil system procedureof measuring capillary pressure was as for the air-brineexcept that the wettability of the core samples was altered tooil-wet
424 Wettability Modification Glycerophtalic paint (Sigma-Aldrich Inc) was dissolved by stirring overnight in acetoneat room temperature Then the solution was placed in a60 cm3 syringe with a 20-gauge blunt tip needle The tip-to-substrate distance was set at 20 cm and the solution wasflowed on the surface of the samples at a rate of 15mLhrwith a syringe pump (KDS100 KD Scientific Inc) as shownin Figures 11(a) and 11(b) The paint solutions used forwettabilitymodification in the experimental work were 2mmthick Samples were then loaded into the ceramic plate afterwettability alteration (Figure 12) Samples whose surfaces
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
![Page 8: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/8.jpg)
8 Journal of Petroleum Engineering
K = 223mdSwi = 5941Swir = 1317
120601 = 3020Soi = 5875Sor = 2472
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
0 10 20 30 40 50 60 70 80 90 100
Sw ()
Sample 84 capillary pressure versus saturationfor both air-brine and air-oil system
(a)
K = 50mdSwi = 8731Swir = 2079
120601 = 2379Soi = 8627Sor = 3400
Sample X capillary pressure versus saturation
35
30
25
20
15
10
5
0
Pc
(psia
)
Air-oilAir-brine
20 30 40 50 60 70 80 90 100
Sw ()
for both air-brine and air-oil system
(b)
Figure 14 119875119888versus 119878
119908(air-brine)
119878unmodand (air-oil system)
119878 mod
Table 2 Air-brine capillary pressures and saturations of the samples(119878unmod)
119875119888(psi) 119878
119882() 119878
119882() 119878
119882() 119878
119882()
Sample 102 Sample 546 Sample 84 Sample X1 9839 9824 9825 99052 9090 9185 9119 91945 8006 8002 8206 82618 6272 6319 6571 671915 4322 4177 4254 487735 1913 1593 1317 2079
Table 3 Air-oil capillary pressures and saturations of the samples(119878 mod )
119875119888(psi) 119878
119900() 119878
119900() 119878
119900() 119878
119900()
Sample 102 Sample 546 Sample 84 Sample X1 9890 9822 9856 1002 9616 9365 9494 98405 9051 8557 8676 90648 8124 7185 7095 813615 6045 5024 5161 627235 2913 2637 2472 3400
To open the cell close the drain valve and the pressurevalve Slowly open the exhaust valve and once the pressure hasbeen vented the cell can be safely openedThe test is completeonce the weights have been obtained at equilibrium for thelast pressure setting After the test is complete the porousplate must be cleaned and prepared for storage or reuse
The testing procedure described above was used for air-brine system whereby the wettability of the core sample wasnot altered (water wet samples) Air-oil tests are performedin the same manner as described above except that a low
viscosity refined mineral oil such as Isopar was used tosaturate the samples and the porous plate Because air-brineand air-oil systems have different surface tension values thepressure settings were different and 05 1 2 5 8 and 15 psiwere used for air-oil system
422 Air-Brine System Capillary Pressure Measurement Inthis study the procedure described above was used for air-brine system in acquiring the capillary pressure data of thecore samples
423 Air-Oil System Capillary Pressure Measurement Air-oil tests are performed in the same manner as for the air-brine system except that the samples and the porous platewere saturated with oil and the pressure settings are 05 12 5 8 and 12 psi In this work the air-oil system procedureof measuring capillary pressure was as for the air-brineexcept that the wettability of the core samples was altered tooil-wet
424 Wettability Modification Glycerophtalic paint (Sigma-Aldrich Inc) was dissolved by stirring overnight in acetoneat room temperature Then the solution was placed in a60 cm3 syringe with a 20-gauge blunt tip needle The tip-to-substrate distance was set at 20 cm and the solution wasflowed on the surface of the samples at a rate of 15mLhrwith a syringe pump (KDS100 KD Scientific Inc) as shownin Figures 11(a) and 11(b) The paint solutions used forwettabilitymodification in the experimental work were 2mmthick Samples were then loaded into the ceramic plate afterwettability alteration (Figure 12) Samples whose surfaces
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
![Page 9: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/9.jpg)
Journal of Petroleum Engineering 9
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-oil Krw
Air-brine Kra
Air-oil Kra
Air-oil Kro
for both air-brine and air-oil systemSample 102 relative permeabilities curves
(a)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 546 relative permeabilities curves
(b)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample 84 relative permeabilities curves
(c)
1
09
08
07
06
05
04
03
02
01
0
1
09
08
07
06
05
04
03
02
01
015 25 35 45 55 65 75 85 95
Air-brine Kra
Air-brine Krw
Air-oil Kra
for both air-brine and air-oil systemSample X relative permeabilities curves
(d)
Figure 15 Relative permeability curves for both (air-brine)119878unmod
and (air-oil system)119878 mod
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
![Page 10: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/10.jpg)
10 Journal of Petroleum Engineering
Table 4 Relative permeability of the core samples(air-oil system)
119878 mod
Core 119875119888(psi) 119878
119900() 119878
119900
lowast () 119870119903119900
119896119903119886
102
1 9890 9845 094 0000007362 9616 9458 080 00003094635 9051 8661 056 00044800778 8124 7353 029 003218576815 6045 4420 004 025059280335 2913 000 000 100
546
1 9822 9758 091 0000027982 9365 9137 070 00012295965 8557 8040 042 0013576828 7185 6177 015 009036062215 5024 3242 001 040871301535 2637 000 000 100
84
1 9856 9808 093 00000139982 9494 9328 076 00005856095 8676 8241 046 00099286578 7095 6141 014 00927769815 5161 3571 002 036055289535 2472 000 000 100
X
1 100 100 100 0002 9840 9758 091 00000281495 90 64 8582 054 00053000998 8136 7176 027 003869205715 6272 4352 004 025863878935 34 000 000 100
(119878119900
lowast is the effective oil saturation)
weremodified were labeled 119878 mod while normal samples werelabeled 119878unmod
5 Results and Discussion
51 Results
511 Results of the Routine Core Analysis In the routine coreanalysis core samples were tested to determined propertiessuch as porosity permeability and saturation percentage ofeach Table 1 below shows the results of that analysis
512 Results of Capillary Pressure Measurements Samplestested ranged from 50md to 232md air permeability (119870
119886119894119903
at ambient) At the maximum air-brine capillary pressurethe selected samples yielded immobile water saturation (119878
119908119894119903)
values between 13 and 22 percent pore volume ( PV)and immobile oil saturation (119878
119900119903) values between 24 and 34
percent pore volume ( PV) For most samples the requestedmaximum air-brineair-oil capillary pressure of 35 psi wasattained
513 Results of the Relative Permeability The results ofrelative permeability of the core samples were estimated
Table 5 Relative permeability of the core samples (air-brine)119878unmod
Core 119875 (psia) 119878119908() 119878
119908
lowast () 119870119903119908
119896119903119886
102
1 9839 9801 092 0000015622 9090 8874 062 0002691515 8006 7534 032 0026280308 6272 5391 008 01507345615 4322 2979 001 04492675035 1913 000 000 100
546
1 9824 9791 091893743 000001812 9185 9030 066501503 000173465 8002 7624 033778045 002365198 6319 5621 009983124 0131166515 4177 3074 000892358 0434441935 1593 000 000 100
84
1 9825 9799 092195527 000001612 9119 8985 065184567 000198315 8206 7934 039628681 001581088 6571 6051 013407959 0098834015 4254 33 82 001308391 0387871235 1317 000 000 100
X
1 9905 9880 095294951 000000342 9194 8982 065087734 000200245 8261 7804 037098481 001884488 6719 5858 01177827 0112667115 4877 3533 001557909 0366027635 2079 000 000 100
(119878119908
lowast is the brine effective saturation)
assuming that the Brooks and Corey formula prescribe theirrelationships (7) the results are presented in the tables
52 Discussion of Results
521 Wettability The tested samples have porosities rang-ing from 23 to 33 with absolute air permeability of50 to 233md and of grain density between 264 gcc and269 gcc The routine core analysis data are good lithol-ogy indicators With these the lithology of the samplesindicates that rock samples are quartz and carbonatesminerals Most common aquifer materials such as quartzcarbonates and sulfates are strongly water-wet and sincethe tested samples are of quartz and carbonates materialsit was therefore assumed that the samples were initiallywater-wet
Surfactants are surface active agents that can be used toalter the wettability of porous rocks There are numerousmethodologies and practices for studying and measuringwettability and its modification The interactions of surfac-tants with reservoir materials to alter wettability are highlydependent upon the pore surface composition and porestructure as well as the characteristics of the surfactantsWettability alteration of porous rock from surfactants canaffect drilling well completion well stimulation secondaryor tertiary oil production and environmental cleanup In this
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
![Page 11: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/11.jpg)
Journal of Petroleum Engineering 11
work thewettability of the core samples was altered to oil-wetusing a surfactant
522 Capillary Pressure From the capillary pressure curvesof the air-brine system the wetting phase (brine) irreduciblesaturation ranged from 13 to 21 while that of the air-oil system (oil) ranged from 25 to 34 The irreduciblesaturation of the wetting phase (119878
119908119894119903) before wettability
alteration (airbrine system for water wet sample) is smallerthan the irreducible saturation of the wetting phase (119878
119900119903) after
the wettability of the samples were changed to oil-wet (air-oilsystem) as shown in Figures 13 and 14 This is as a result offractional wettability alteration of the core samples Figures11(a) and 11(b) show how the wettability of the core samplewas changed by smearing paint on some surface faces of thecores The saturation history of the core samples before andafter wettability alteration also differs It can be seen fromTables 2 and 3 that for an air-brine system the nonwettingphase (air) easily displaces the wetting phase while for anair-oil system the displacement of the wetting phase (oil) islower This is as a result of fractional wettability alteration ofthe porous rock
523 Relative Permeability Tables 4 and 5 present the resultsof the relative permeability of the core samples for air-brinesystem and air-oil systems From these tables and Figures15(a)ndash15(d) we see that the relative permeabilities of thewetting phase for an air-brine system are lower than therelative permeabilities of the wetting phase for an air-oilsystem while it is the opposite for their nonwetting phaserelative permeabilitiesThis shows that altering thewettabilityof the core samples from water-wet to oil-wet increases therelative permeability of the wetting phaseThis shows that oilrecovery can be improved using this method
6 Conclusion
This study has shown howwettability alteration of an initiallywater-wet reservoir rock to oil-wet reservoir rock affects theproperties that govern multiphase flow in porous media thatis capillary pressure relative permeability and irreduciblesaturation Initial water-wet reservoir core samples withporosities of 23 to 33 absolute air permeability of 50 to233md and initial saturation (brine) of 63 to 87 werefirst tested as water wet samples under air-brine system Thisyielded an irreducible wetting phase saturation of 19 to 21The samples were later tested aftermodifying their wettabilityto oil-wet using a surfactant and a wetting phase irreduciblesaturation (oil) of 25 to 34 was obtained From the resultsof these experiments changing the wettability of the testedsamples to oil-wet using a surfactant enables us to improvethe recovery possibility of the wetting phase (oil)
Nomenclature
1198601 Area under the oil-displacing brine curve
1198602 Area under the brine-displacing oil curve
119868 Amott wettability index
119896 Permeability119871 Length or characteristic length of core
samples119873119908 USBM wettability number
119875 Pressure119902 Imbibition rate1199031 1199032 Are the principal radii of curvature of the
interface between the two fluids in thecapillary tube
119877 Oil (or nonwetting phase) recovery orig-inal oil in place
119878 Saturationmod Modified sample119878unmod unmodified sample119905 time119879 Temperature119881119901 Pore volume
119904 Spontaneous
Subscripts
119886 Aging119860 AdvancingAH Amott-Harvey119888 Critical119888 Capillary or characteristic119889 Dynamic119863 Dimensionless119864 Equilibrium119891 Flooding119892 Gas119894 Initialim Imbibition119900 Oil119900119903 Residual oilps Pseudo119903119892 Gas relative permeability
119877 Relativesww Strongly water-wet119908 Water
Greek
Δ Difference120579 Contact angle120583 ViscosityΣ Area under capillary pressure curve120590 Interfacial tension IFT120601 Porosity
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F F Craig The Reservoir Engineering Aspects of Waterfloodingvol 3 of SPE Monograph Richardson Tex USA 1971
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
![Page 12: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/12.jpg)
12 Journal of Petroleum Engineering
[2] N R Morrow and J C Melrose ldquoApplication of capillarypressure measurements to the determination of connate watersaturationrdquo in Interfacial Phenomena in Petroleum Recovery NR Morrow Ed pp 257ndash287 Marcel Dekker New York NYUSA 1991
[3] A W Adamson Physical Chemistry of Surfaces John Wiley ampSons 6th edition 1990
[4] W G Anderson ldquoWettability literature survey-part 1rockoilbrine interactions and the effects of core handling onwettabilityrdquo Journal of Petroleum Technology vol 38 no 11 pp1125ndash1144 1986
[5] N RMorrow ldquoWettability and its effect on oil recoveryrdquo Journalof Petroleum Technology vol 42 no 12 pp 1476ndash1484 1990
[6] A Graue E Aspenes T Bognoslash R W Moe and J RamsdalldquoAlteration of wettability and wettability heterogeneityrdquo Journalof Petroleum Science and Engineering vol 33 no 1ndash3 pp 3ndash172002
[7] M N Derahman andM K Zahoor ldquoPrediction and estimationof capillary pressure for wettability and wettability variationswithin reservoirrdquo in Proceedings of the 13th Abu Dhabi Interna-tional Petroleum Exhibition and Conference (ADIPEC rsquo08) pp591ndash609 November 2008
[8] L W Lake Enhanced Oil Recovery Prentice-Hall EnglewoodCliffs NJ USA 1989
[9] S K Masalmeh X D Jing W van Vark H van der Weerd SChristiansen and J van Dorp ldquoImpact of SCAL on carbonatereservoirs how capillary forces can affect field performancepredictionsrdquo in Proceedings of the International Symposium ofthe Society of Core Analysts (SCA rsquo03) SCA 2003-36 PauFrance October 2003
[10] D W Ruth and Z A Chen ldquoMeasurement and interpretationof centrifuge capillary pressure curvesmdashthe SCA survey datardquoThe Log Analyst vol 36 no 5 pp 21ndash33 1995
[11] G R Jerauld and S J Salter ldquoThe effect of pore-structure onhysteresis in relative permeability and capillary pressure pore-levelmodelingrdquoTransport in PorousMedia vol 5 no 2 pp 103ndash151 1990
[12] M Honarpur L Koederitz and A H Harvey Relative Perme-ability of Petroleum Reservoirs CRC Press 1986
[13] P H Valvatne and M J Blunt ldquoPredictive pore-scale modelingof two-phase flow in mixed wet mediardquo Water ResourcesResearch vol 40 no 7 Article ID W07406 2004
[14] S AL-Sayari and M Blunt ldquoThe Effect of wettability onrelative permeability capillary pressure electrical resistivity andNMRrdquo inBenchmark Experiments onMultiphase Flow ImperialCollege of London 2012
[15] M T Al-Garni and B D Al-Anazi ldquoInvestigation of wettabilityeffects on capillary pressure and irreducible saturation forSaudi crude oils using rock centrifugerdquo Oil and Gas Business2008
[16] D P Green J R Dick M McAloon P F D J Cano-BarritaJ Burger and B Balcom ldquoOilwater imbibition and drainagecapillary pressure determined by MRI on a wide sampling ofrocksrdquo in Proceedings of the 22nd International Symposium ofthe Society of Core Analysts Abu Dhabi UAE 2008
[17] J Chen G J Hirasaki andM Flaum ldquoNMRwettability indiceseffect of OBM on wettability and NMR responsesrdquo Journal ofPetroleum Science and Engineering vol 52 no 1ndash4 pp 161ndash1712006
[18] D M OrsquoCarroll L M Abriola C A Polityka S A Brad-ford and A H Demond ldquoPrediction of two-phase capillary
pressure-saturation relationships in fractional wettability sys-temsrdquo Journal of Contaminant Hydrology vol 77 no 4 pp 247ndash270 2005
[19] S Bekri C Nardi and O Vizika ldquoEffect of wettability onthe petrophysical parameters of vuggy carbonates networkmodeling investigationrdquo in Proceedings of the InternationalSymposium of the Society of Core Analysts held in Abu DhabiUAE October 2004
[20] K Li and A Firoozabadi ldquoExperimental study of wettabilityalteration to preferential gas-wetting in porous media and itseffectsrdquo SPE Reservoir Evaluation amp Engineering vol 3 no 2pp 139ndash149 2000
[21] M-HHui andM J Blunt ldquoEffects of wettability on three-phaseflow in porous mediardquo Journal of Physical Chemistry B vol 104no 16 pp 3833ndash3845 2000
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
![Page 13: Research Article Wettability Effects on Capillary Pressure ...downloads.hindawi.com/archive/2014/465418.pdf · ected by the capillary pressure of the rock [ ]. By de nition, the capillary](https://reader033.fdocuments.net/reader033/viewer/2022060305/5f0963ad7e708231d4269abe/html5/thumbnails/13.jpg)
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
