1 Procesos de EOR en NFR Taller 2

EOR Processes and Reservoir Characterization in NFRs –The Cantarell, Ku, Maloob, and Zaap Fields

Tayfun Babadagli, PhD, PEngProfessor of Petroleum Engineering

University of AlbertaDept. of Civil and Env. Eng., School of Mining and Petroleum

Edmonton, Alberta, [email protected]

URL: www.ualberta.ca/~tayfun

PEMEX Workshop, Ciudad del Carmen, 9-13 November 2009

EOR Processes in NFR – Workshop -2

2Tayfun Babadagli, PhD, PEng PEMEX Workshop 9-13 November 2009 File-1

OBJECTIVE

DAY-1: Reservoir Characterization for NFVR (Naturally Fractured – VuggyReservoirs): What are the problems in NFVR characterization? What are the problems in NFR development (drilling, production, well and reservoir management, completion, modeling, data gathering, EOR) in relations to the characterization. Pore scale characterization of NFVR. Tools used for larger scale characterization: Cores, outcrops, logs, drilling data, well tests. Heterogeneity, permeability distributions. Use of different logs (resistivity, radioactive and sonic logs) in reservoir characterization. Estimation of porosity, porosity-permeability correlations, the use of NMR logs in permeability estimation. From geology to petrophysics, production data to wells tests reservoir characterization of NFVR.

DAY-2: Reservoir Characterization for NFVR. Use of well test analysis in reservoir characterization. Basic principles, use of different well tests for reservoir characterization. Type curve and derivative analysis. Pitfalls in well test interpretations. Characterization of naturally fractured reservoirs through well testing.


DAY-3: Use of fractal geometry and stochastic techniques in reservoir characterization. Definition of fractal dimension, self-similar and self-affine fractals. Analysis of logs using fractal techniques. Generation of representative static reservoir models. Concept of stochastic modeling. Fracture surface characterization. Fracture networks. Use of fractal geometry in characterization of fracture surfaces and networks. Use of pressure transient analysis and tracer tests in fracture network characterization and mapping fracture network permeability. Using production data in reservoir and fracture swarm characterization. Practical modeling of fracture network permeability.

DAY-4: Selection of EOR process in NFVR: Immiscible, miscible, thermal, chemical techniques in NVFR. Heavy-oil vs. light oil. Laboratory analyses and field cases. Followed by a discussion period.

DAY-5: EOR methods applicable to offshore NFVR with 28-38 API and water and gas production problems due to active aquifer and gas cap.Current and potential applications in RMNO fields. Field examples analog: The Yates, Bati Raman, Spraberry, Qarn Alam, Midale-Weyburn, Yibal, Ekofisk, North Sea fields etc. Followed by a discussion period.


DISCUSSION ON Abkatun-Pol-Chuc, Caan: Selection of EOR process applicable to offshore NFVR with 28 API and water and gas production problems due to active aquifer. There is oil in the matrix surrounded by water or by gas. Dimensionless groups to characterize different EOR Processes in Abkatun-Pol-Chuc in order to select the appropriate EOR Process.

DISCUSSION ON Light oils: EOR process applicable to offshore NFVR with 28-38 API High Pressure (active aquifers) and High temperature in the reservoir. Cluster of small offshore reservoirs. Dimensionless groups to characterize different EOR Processes in order to select the appropriate EOR Process.


Fractures provide no additional porosity or permeability but create significant reservoir

heterogeneity (Barrier)Type 4

Kirkuk, Iraq Gachsaran, Iran Hassi Messaoud,

Algeria

Fractures assist permeability in an already producible reservoirType 3

Agha Jari, Iran Haft Kel, Iran

Spraberry, TexasFractures provide the essential permeabilityType 2

Amal, Libya Edison, California

Wolf Springs, Montana

Fractures provide the essential reservoir porosity and permeabilityType 1

ExampleDefinitionNFR Type

Type of Fracture Reservoirs


Common fracture styles, their displacements, and their orientations relative to principal stress orientations common in the Earth’s upper crust (after Narr et al. 2006).


EXPERIMENTAL FRACTURES•Shear•Extension•Tensile

NATURAL FRACTURES•Tectonic (due to surface forces)•Regional (surface or body forces)•Contractional (body forces)•Surface related (body forces)

FRACTURE CLASSIFICATION


TYPICAL FOLD RELATED FRACTURE ORIENTATIONS


Nelson, 2001

TECTONIC FRACTURES


Nelson, 2001

CONJUGATE FOLD-RELATED FRACTURES


Nelson, 2001

CONTRACTIONAL FRACTURES


Tectonic fracture intensity


(After Nelson, 2001)


Fractures provide essential porosity and permeability



Fractures provide essential permeability



Fractures provide essential porosity and permeability Fractures provide permeability assist



Fractures provide essential permeability



LPlbq Δ

=μ12

3

1

12

2bK f =

SetsFracturenForD

eD

eKK

n

nnmfm →+++= 1

12cos

...12cos 23

1

123

1 αα

xpbv f ∂

∂−=

μ12

2L

l

bL

FRACTURE PERMEABILITY


)}/12/1)(0(exp{ DKK geff −= ρ King, 1987

Bogdanov et al. (2003)

FRACTURE PERMEABILITY


(after Hestir and Long, 1990)

cc pppppP >− βα )()(μα )( cppK − Stauffer and Aharony (1994) proposed the following general

scaling law between the conductivity (or permeability) and percolation threshold and exponent

PERCOLATION THEORY


(after Hestir and Long, 1990)

Zhang and Sanderson (2002), d=fracture density pcp ddAK )( −=

)'(' 32 ρσρ KAK p ⟩⟨= Mourzenko et al. (2005)


• Fractal feature of fracture networks.• Fractal geometry ~ network

permeability.– Fractal dimension @ percolation of

fracture network (experimental work).• Fractal distribution of permeability -

upscaling.

CURRENT ISSUES


D = ? @ Percolation Threshold ( D = 1.35 ???, Barton)


Selected percolation thresholds for various lattices. Site refers to site percolation and bond refers to bond percolation

(after Stauffer and Aharony, 1994).

0.07870.089D = 7 hypercubic




0.1190.198FCC

0.18030.246BCC

0.24880.3116Simple Cube

0.3880.43Diamond

0.347290.5Triangular

0.50.592746Square

0.652710.6962Honeycomb

BondSiteLattice


cpNear the critical percolation threshold , the following scaling law exist:

Percolation probability

Accessible fraction

Backbone fraction

Correlation length

Effective conductivity

Permeability of a percolation network. e

c

ce

vcp

cB

cA

c

pppK

pppg

ppp

pppX

pppX

pppP

B

p

p

)()(

)()(

||)(

)()(

)()(

)()(

−≈

−≈

−≈

−≈

−≈

−≈

−

μ

β

β

β

ξ

The exponents in the above scaling law are universal and their values are presented in the following slide.


Values of critical exponents of percolation (after Sahimi, 1993).

pβ

Bβ

v

μ 2.01.3

0.884/3

1.050.47

0.415/36

D = 3D = 2Exponent


(after Mourzenko et al. 2005).

)'(' 32 ρσρ KAK p ⟩⟨=

ρ

σ

pA

2'K

3'ρ

⟩⟨ pAσρ

is fracture density,

is fracture conductivity coefficient,

is surface area,

is dimensionless permeability and

is dimensionless density. The extensive term

represents the volumetric area of fractures, weighted by the individual fracture conductivities.


Dual continuum and discrete fracture network concepts (after Dershowitz et al. 1998)


Porous media equivalent

as SDK 113'6.07.110 +−−=)8/(2 FRK =DDK /)4( −≈φ

)]()[21 )/(' vvss EDDE

nllCK −+−= φ

)}/12/1)(0(exp{ DKK geff −= ρ

SetsFracturenForD

eD

eKK

n

nnmfm →+++= 1

12cos

...12cos 23

1

123

1 αα


UNSWEPT AREA:

• Viscous fingering or capillary trapping (micro scale).• Mobility ratio or channeling or heterogeneity (larger scales)


q=1 cc/min

Matrix : 0.35 mmFracture : -

Oil Vis. = 2.2 cp

20 cm

12 c

m

3.5 cc

6.5 cc

14 cc

15 cc

Water


q=1 cc/min q = 2.5 cc/min

3.5 cc

7.5 cc

17 cc

24 cc

3.5 cc

5 cc

15 cc

35 cc


WHAT IS Sor (SWEPT ZONE)In water wet rock, residual oil is trapped in a pore. If the capillary forces are greater than the force of driving fluid, trapping occurs.

GRAIN

OIL BLOBWATER P1 P

2

P1 P2FOR DISPLACEMENT OF OIL BLOB


Mobilization of Oil Blob

DARCY LAW YOUNG-LAPLACE

kLqPP w

1μΔ ==

rCos2PPPP cwnw2

θγ==−=

>μk

Lq wr

Cos2 θγ

For mobilization of oil blob

Lr)Cos(2q

wμθγ

>

v = injection velocity μw = water viscosity γow = interfacial tension θ = contact anglek = permeability r = pore size L = pore length q = injection rate

Since k ~ r2, then

)Cos(vN w

ca θγμ

=


v = injection velocity μw = water viscosityγow = interfacial tension θ = contact anglek = permeability r = pore sizeL = pore length q = injection rate

capillaryviscousvN

ow

wca ==

γμ

CAPILLARY NUMBER, Nca


From Stegemeir (Improved Oil Rec. by Surf. And Polymer Flooding, 1977)

Immiscible Miscible


capillaryviscousvN

ow

wca ==

γμ

owca

LPk

NγΔΔ

=LPkv

ΔΔ

μ=

•In reservoir it is not practical to increase significantly the pressure differential between injection and production well over that ofwaterflood.•Infill drilling feasibly reduce the interwell distance (ΔL) by no more than a factor of two or four.•The only way to reduce the Nca the four orders of magnitude required to reduce the ROS is to reduce the IFT.

BEREA SANDSTONE

75 μm


Modified capillary number for waterfloods at constant injection rates:

4.0

mod )cos()( ⎟⎟⎠

⎞⎜⎜⎝

⎛−

=−o

w

oroi

wca

owSS

vNμμ

θγμ

After Abrams, SPEJ Oct. 1975.

A field scale capillary number was defined for 5-spot pattern as follows:

u : superficial water velocityk : absolute permeabilityko

rw : end-point water relative permeabilityΔP : injector-producer pressure dropA : pattern aread : injector producer distancerw : well radius

⎟⎟⎠

⎞⎜⎜⎝

⎛−

Δ=

619.0ln

10

ww

orw

w

rdA

Pkku

μ)Cos(vN w

ca θγμ

=

da

P


DISPLACEMENT IN OIL–WET AND WATER–WET MEDIA

GRAIN

WATER

OIL WET

OILGRAIN

WATER

OIL WET

OILGRAIN

WATER

OIL WET

OIL

GRAIN

WATER

WATER WET

OIL

GRAIN

WATER

WATER WET

OIL

GRAIN

WATER

WATER WET

OIL


Jadhunandan and Morrow, SPE 22597, 1991


WATER INJECTED, PV

8070605040302010

0 1 2 3 4 5 6 7 8 9 10

WATER WETMIXED WET

Oil Saturation(%)


CALCITE

WATER

NAPHTHENIC ACID

θ = 106o

SANDSTONE

WATER

NAPHTHENIC ACID

θ = 35o

θ is the only measure of WETTABILITY

Sandstone : Water-wet, Carbonates: Oil-wetWettability changes with pH, organic compounds existing, rock type.(A good review of wettability by N. Morrow, JPT Dec. 1990, 1476-1484, SPE 21621)

WETTABILITY OF DIFFERENT ROCK TYPES


INTERFACIAL TENSION (IFT)

There exists a few molecule thick zone at the interface between twoimmiscible fluids. At this zone, molecular attraction is different than inside.

van der Walls forces (F~ (… )/r7 )

and

electrostatic forces (F~ (… )/r2 )

WATEROIL


INTERFACIAL TENSION (γ) = FORCE / LENGTH = DYNE / CM(WORK/AREA)

IF γ > 0 IMMISCIBLE IF γ = 0 MISCIBLE

γo-w = 10-30 dyne/cm @ 75 oFγsteam-w = 70 dyne/cm (Surface tension, ST)

IFT < ST, IFT decreases with increasing temperature and pressure.

INTERFACIAL TENSION (IFT)


CAPILLARY PRESSURE, PC

θ hOIL

WATER

CAPILLARY TUBE

r2*AForceUp T Π=)cos(A OWWSOST θγγγ =−=

)r(hgForceDown 2Πρ=

ρθγ hgr

)cos(2PPP wnwc ==−=

CA

PILL

AR

Y PR

ESSU

RE,

psi

0 100 WATER SATURATION, %

DRAINAGE (nw-w)

IMBIBITION (w-nw)


RELATIVE PERMEABILITY, kr

DARCY is no longer valid when two immiscible fluids flow in porous medium. In this case flow depends on saturation, viscosity ratio contact angle, capillary number and time.

kro = ko/k, krg = kg/k, krw=kw/k

REL

ATI

VE P

ERM

EAB

ILIT

Y, k

r

0 100 WATER SATURATION, %

Swi S or

Oil

Water

1WATER WET

50

REL

ATI

VE P

ERM

EAB

ILIT

Y, k

r0 100 WATER SATURATION, %

Swi Sor

Oil

Water

1OIL WET

50


0 1

1

0

Rel

ativ

e P

erm

eabi

lity

krw

kro

Swi 1-Sor

RELATIVE PERMEABILITY

Sw, fraction

2 = Recoverable OilReserves

31 2

1 = OOIP (1-Swi)(Logs, Pc, SCAL)

3 = Residual OilSCAL, logs, MB

HOW FAST

HOW MUCH


DETERMINATION OF RESIDUAL OIL SATURATION

METHODS

•Core Analysis•Logs•Volumetric-Reservoir Engineering Studies•Production Data•Chemical Tracers•Well Testing (need support from core analysis)


ADVANTAGES - DISADVANTAGES•Volumetric-Reservoir Engineering Studies:

Remaining after waterflood but no information aboutthe oil distribution

•Chemical Tracers:Distribution

122912

12

ROS fromTracer Test

Oil in isolated pockets. Infill.444

Tertiary oil recovery (TOR)403

Oil in isolated pockets. Infill.252

Both low, no TOR. More wells between producers

161

ROS fromMaterial Balance

(% PV)

Field

Data from: Determination of Residual Oil Saturation, D.C. Bond, C.R. Hocott, F.H. Poettmann (Editors), Interstate Oil Compact Comm., Oklahama City, OK, 1978


FLUID SATURATIONS by CORE ANALYSIS

•Vacuum distillation•Distillation (water) -Extraction (oil) using solvents•High temperature retorting (@atmospheric P and 1200 oF)

Average waterflood residual oil in the reservoir (flooded region)

Average waterflood residual oil from coresBo Formation Volume Factor of OilE Bleeding Factor = 1.1M Mobility RatioV Permeability Variation

Kazemi (JPT Jan. 1977)

( ) ( ) 2ocoreoreso V1MEBSS−

=

( )resoS

( )coresoS


RESIDUAL OIL

SOR (core, log, tracer) < SOR (Material Balance)SOR (PNC) = SOR (Resistivity logs)SOR (Single well tracer) < (SOR (logs)


0

5

10

15

20

25

30

35

40

45

50S

ampl

e 1

Sam

ple

2

Sam

ple

3

Sam

ple

4

Sam

ple

5

Sam

ple

6

Sam

ple

7

Sam

ple

8

Sam

ple

9

Sam

ple

10

Sam

ple

11

Sam

ple

12

Sam

ple

13

Sam

ple

14

Sam

ple

15

Sam

ple

16

Sam

ple

17

Sam

ple

18

Sam

ple

19

Sam

ple

20

Sam

ple

21

Sam

ple

22

Sam

ple

23

Sam

ple

24

Sam

ple

25

Sam

ple

26

Sam

ple

27

Sam

ple

28

Sam

ple

29

Sam

ple

31

Sam

ple

32

Sam

ple

33

Resi

dual

Oil,

%

Material Balance Resistivityogs PNC (Log-Inject-Log) Core (pressure) WOR-Rel. Perm.

Babadagli, T. SPE 93884, produced using the data from: Determination of Residual Oil Saturation, D.C. Bond, C.R. Hocott, F.H. Poettmann (Editors), Interstate Oil Compact Comm., Oklahoma City, OK, 1978

Residual Oil Saturations for Different (US) Sandstone Oil Reservoirs

MEASUREMENT OF RELATIVE PERMEABILITY, kr

Although there exist analytical, statistical and stochastic techniques, the most reliable way of obtaining kr curves is the experimental methods.

There exist three methods:

1. Steady State: Calculation is simple - relies on Darcy’s Equation - but the experimentation takes longer time.

2. Unsteady State: Easier to measure but longer calculation time is required for JBN and Welge techniques.

3. Centrifuge: Less common than other two methods.


qwiqoi qoL

qwL

L

Poi

Pwi

PoL

PWL

w

wwrw PkA

LqkΔ

μ=

o

ooro PkA

Lqk

Δ=

μ

STEADY STATE

• The experimental procedure is difficult and time consuming• Calculation is simple

End effect is a problem.


UNSTEADY STATE

qwi qT = qwL + qoL

L

P1 P2

Difficulty arises due to capillary end effect, viscous fingering and the effort required for the computations.


CENTRIFUGE

•A fast technique based on unsteady-state flow.

•Relative permeabilities are determined by mathematical models.

•Viscous fingering is avoided.

•Does it really represent the flow process in reservoir?


SO, WHICH METHOD IS GOOD? (SPE 18292, SPE 28826)

Experiments Reservoir Displacement Processes

Waterflooding GOGD WAG

Steady-state: Does not resemble to displacement but fast.

X X

Unsteady-state:Indirect but fast and resembles to flooding in reservoir

X X

Centrifuge: Indirect, fast but not proven for water/oil systems.

X X X


After Bardon and Longeron, 1978 SPE AIME

IFT


WETTABILITY

After Donaldson and Crocker, US DOE Report BERC/RI-77/15, Dec. 1977.


THREE PHASE RELATIVE PERMEABILITY(TERTIARY RECOVERY)

•GOGD (Gas Oil Gravity Drainage)•Waterflood•Steamflood•Immiscible gas flooding•Water alternating gas•Chemical flooding

Corey: Gas-oil measured at the presence of connate water

Stone: Only kro is a function of both water and gas saturationPorous media is water-wet


THREE PHASE RELATIVE PERMEABILITY(TERTIARY RECOVERY)

•More hysterisis in USS curves than in SS curves.•USS curves indicate more oil-wet conditions.•Owing to a different trapping mechanism, gas RP curves showed much•Weaker dependence on the direction of gas saturation change under SS compared to the USS •SS more reliable!

For strong-wetting conditions : SS is more reliable


NATURALLY FRACTURED RESERVOIRS - NFR

Data acquisition ????? Reservoir simulation

Dilemma: How to incorporate different (and limited) data sets and map the fracture network.

NFR characterization is mainly based on the fracture sets seen in the logs and cores.


CORES:

Used to determine:

Origin, geometry and occurrence of fractures

Geomechanical modification

Fracture orientation

Fracture dip relative to core axis and to bedding, as well as relative orientation of fractures should be measured.

Fracture aperture and height: Needed for fracture density, porosity, etc.

After Narr, Schechter, Thompson“Naturally Fractured Reservoir Characterization” SPE, 2006


IMAGE LOGS

Direct source of information.Two types; resistivity based and acoustic.

(a)Open fractures in resistivity image (dark sinusoids), (b) Core form the same well, (c) image of whole core

(Courtesy Frank Lim, NFR SPE)



Apparent fracture height can be measured from image logs.

Open fractures: filled with conductive mud filtrate

Closed fractures: filled with resistive mineralization

Image logs are good for orientations. Aperture could also be computed.



FRACTURE DENSITY

Fracture surfaces area/unit volume

Fracture surface area : computed form cores or image logs.

rr hDV2

2⎟⎠⎞

⎜⎝⎛Π=

r

n

ifi

r

n

ifi

f Dh

h

V

Ad

ff

∑∑== == 11

L2/L3 is reduced to 1/L. For a set of parallel fractures, L is equal to their average spacing (perpendicular distance between fractures).

Fracture density provides fracture spacing

r

n

ififi

r

n

ififi

f Dh

ha

V

Aaff

∑∑== == 11φ

af is fracture aperture.


Fracture Permeability

12

2o

fWk = Muskat Eq.

swk o

f 12

3

= Lamb’s Equation

If w is in inches (IF=# fractures/ft) IFwk f **10*54.4 36=

If w is in cm (IF=# fractures/ft) IFwk f **10*77.2 35=

DIRECT PROPORTIONALITY!!!!


Nelson, R.A. Geological Analysis of Naturally Fractured Reservoirs, Gulf Publ. 2001

FRACTURE SPACING

Calculated in core and outcrops by counting the number of fractures encountered along a line of some given length perpendicular to the fracture set an dividing the length of measurement line.

In more complex environments, the same is done along lines in specific dimensions.

1 Procesos de EOR en NFR Taller 2

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