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Sampling Viscous Oil Sands
Sampling, Preserving and Testing Heavy Sampling, Preserving and Testing Heavy Oil Sand Cores Oil Sand Cores
Maurice Dusseault
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Sampling Viscous Oil Sands
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Sampling Viscous Oil Sands
Canadian ExperienceCanadian Experience
Heavy oil core samples exhibit expansion of 1% to as much as 12%
Lab values of = 34-40% are quite common
Porosities in the ground, calculated from geophysical logs, are consistent – 29-31%
Reservoir parameters based on expanded core samples can give serious problems
The expansion cannot be fully reversed by using overburden pressures on specimens
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Sampling Viscous Oil Sands
International ExperienceInternational Experience
Kazakhstan - Karazhanbas - largest heavy oil field in the FSU – core damage issues
Venezuela – Orinoco Extra Heavy Oil Sands – largest extra heavy oil deposit in the world – severe core damage issues
China – Liaohe and Karamay – damaged heavy oil sands core leads to problems
Colombia – Magdalena heavy oil fields – damage leads to poor choice of technology
Oman, Ecuador, USA, …
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Sampling Viscous Oil Sands
Karazhanbasmunai(i.e. Karazhanbas
Oilfield)
Aktau
KARAZHANBASMUNAI - KZKARAZHANBASMUNAI - KZ
Kashagan Tengiz
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Sampling Viscous Oil Sands
Study AreaStudy Area
Roads
O il P ipelines
Ku lsa ry
TENG IZ
N. BUZACHI (Texaco)
ARM AN(Kerr-M cG ee)
KARAZHANBA SSHE LF
Te n giz
Aktau
C A S P I A NS E A
KALAM KAS(M M G )
As trakhan
Atyrau
K arazhanbas(NECL )
PreCaspian Basin
Roads
O il P ipelines
Ku lsa ry
TENG IZ
N. BUZACHI (Texaco)
ARM AN(Kerr-M cG ee)
KARAZHANBA SSHE LF
Te n giz
Aktau
C A S P I A NS E A
KALAM KAS(M M G )
As trakhan
Atyrau
K arazhanbas(NECL )
PreCaspian Basin
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Sampling Viscous Oil Sands
The ProblemsThe Problems
Data, based on core analyses only, gave… Porosities of 33-38% (~31%) Permeabilities of 4-8 D (~2-3D) Gas saturation of 1-8% (Sg = 0)
High kw (low kw)
The field was operated on a 50% production share basis. Issues… Service company problems (core tests…) Regulatory agency problems (KZ - CDC) Poor predictions of recovery and rates Poor choice of technology
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Sampling Viscous Oil Sands
Faja del Orinoco (XH Oil)Faja del Orinoco (XH Oil)
Extra-heavy crude oil deposits
> 1.21012 BOIP ~ 0.30, z ~ 450-
800 m, So ~ 0.88 Unconsolidated Estimated 25%
recoverable with current methods
SAGD – CHOPS – HWCS …
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Sampling Viscous Oil Sands
Faja del OrinocoFaja del Orinoco
-On the order of 200109 m3 OOIP
-1000-6000 cP oil, <10ºAPI
- = 30%, k = 1-15 D
-z = 300-700 m
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Sampling Viscous Oil Sands
Faja StratigraphyFaja Stratigraphy
Cambrian/Cretaceous sedimentary rocks
Architecture
Lo
wer
del
ta p
lain
Up
per
del
ta p
lain
Seq.
Strat.
MFS
Top F
Top E2
Top E1
Top D3
Top D2
Top D1
M14
Base level cycles GR
200
ft
Lo
ng
ter
m b
ase
leve
l ris
e
Lo
ng
ter
m b
ase
leve
l fal
l
E2F
E1
D3
D1
C2
C1
B
A
D2
TS/MFS
Unconformity
M9
M1
MFS
Base F.
MFS
MFS
16.8
17.0
17.3
17.1
19.1
23.8
Ma
Allu
vial
/Up
per
del
ta p
lain
M12
DELTAIC
FLUVIAL
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Sampling Viscous Oil Sands
The ProblemsThe Problems
Core damage led to: Excessively high permeabilities High lab compressibilities (40-10010-6 psi-1)
This led to a “belief” in compaction drive Lake Maracaibo heavy oil reservoirs benefit
substantially from compaction drive Vast sums of money and field experiments
Based on expanded core properties Finally, in the 1990’s, the issue disappeared,
but only after much time and money was spent
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Sampling Viscous Oil Sands
Evidence of Core DamageEvidence of Core Damage
Porosity vs. Permeability - Edam Core
0.25
0.270.29
0.310.33
0.350.37
0.390.41
0.43
0 1000 2000 3000 4000 5000 6000 7000
Permeability - mD
Po
ros
ity
Typical value, good heavy oil sands: 31%
EDAM Field, Well 15-29EDAM Field, Well 15-29
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Sampling Viscous Oil Sands
Edam Core, Well 7-30Edam Core, Well 7-30
Porosity vs. Permeability - Edam Core: 7-30
0.20.220.240.260.28
0.30.320.340.360.38
0.4
0 2000 4000 6000 8000
Permeability - mD
Po
ros
ity
Typical value, good heavy oil sands: 31%
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Sampling Viscous Oil Sands
Well 13-29 – Edam FieldWell 13-29 – Edam Field
Porosity vs. Permeability - Edam Core: 13-29
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0 2000 4000 6000 8000 10000
Permeability - mD
Po
ros
ity
Typical value, good heavy oil sands: 31%
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Sampling Viscous Oil Sands
Edam Well 6-29 Edam Well 6-29
Porosity vs. Permeability - Edam Core: 06-29
0.2
0.220.24
0.26
0.280.3
0.32
0.340.36
0.38
0 1000 2000 3000 4000 5000 6000 7000
Permeability - mD
Po
ros
ity
Typical value, good heavy oil sands: 31%
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Sampling Viscous Oil Sands
Conclusions from Edam CoreConclusions from Edam Core
Lab porosities are consistently too high The “correction factor” is not consistent among
different wells Different coring practices and operators Different hardware Different treatment in transport, storage, lab
The differences are not trivial We may expect other properties to be affected,
often to the detriment of the company Can these issues be resolved?
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Sampling Viscous Oil Sands
Evidence of Core ExpansionEvidence of Core Expansion
Observed Expansions of 89mm Core: Ironstone 89 mm Basal clays, clayey silts 89-91 mm Oil-poor to oil-free silty sands 90-93 mm Fine-grained oil-rich sand 91-95 mm Coarse-grained oil-rich sand 94-95 mm
ref. Dusseault (1980) Fig. 5 & 6
Gas pressure inside liner
Core has expanded from 120.7mm to 127mm diameter and is now acting like a piston in a cylinder
Radially Axially
Schematic Diagram of Expansion of an 89 mm Core
PVC
liner
Oil sandIronstone band, no expansion
Oil-poor to oil-free silty sands, expansion much less than other material
Corrugated surface characteristic of thinly-bedded and laminated fine-grained sands of variable oil saturation
Cores separate readily along cracks which form between zones of differing expansion potential
89 mm90-91 mm
Oil-rich sample expands to completely fill the liner
95 mm
127 mm
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Sampling Viscous Oil Sands
Reasons for Core ExpansionReasons for Core Expansion
CH4 present in solution, exsolves during the Δp in bringing core to surface
The high oil content means a lot of gas High μ oil means gas cannot drain; no
continuous gas phase is formed without ΔV The sand is cohesionless (To = 0); it cannot
resist internal expansion The core barrel liners are 7%-13% oversize,
allowing a lot of expansion
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Sampling Viscous Oil Sands
Heavy Oil Cores, MR
Scans
Courtesy of Glen Brook, Nexen and
Apostolos Kantzas, U of
Calgary
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Sampling Viscous Oil Sands
CT-Scan Evidence of Damage in Heavy Oil CoresCourtesy of Glen Brook, Nexen and Apostolos Kantzas, U of Calgary
decr
easi
ng
den
sity
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Sampling Viscous Oil Sands
Core Damage ConsequencesCore Damage Consequences
Porosity overestimated Permeability measurements in the lab are too
high by a factor of ~1.5 to 2 Laboratory data for So, Sw, Sg are wrong Reserve estimation can be out by 5-10% Predicted productivity index by factor of 2 All rock mechanics data are in error
Compressibilities are too high by a factor of >10 Rock strength predictions far too low Etc…
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Sampling Viscous Oil Sands
History…History…
“Evaluation of the Alberta Tar Sands”Sah, Chase, & WellsSPE 5034 (1974)
Old Problems… These issues are “re-
discovered” repeatedly However, the issue is
relatively well-documented (SPE, CJPT, conferences…)
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Sampling Viscous Oil Sands
Empirical EvidenceEmpirical EvidenceZwicky and Eade (Shell) UNITAR, 1977Zwicky and Eade (Shell) UNITAR, 1977
-39-121931Water Saturation
+17+128169Tar Saturation
-10-3.532.035.5Porosity
Percent change
DifferenceDensity Log
Core Analysis
Table 3. Comparison of results from core analysis alone and density from logs, Lease 13, average data
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Sampling Viscous Oil Sands
Log Derived PorosityLog Derived Porosity
Neutron porosity is not a true measure of porosity (it actually is a measure of H)
Determine the true density using a gamma-gamma density log (average over 1 m)
Calculate based on this density number Heavy oil sands in situ are almost always
liquid saturated (i.e.: Sg = 0) Determine saturations from cores Some factors (grain size, mineralogy, liquid
densities…) are not affected by expansion
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Sampling Viscous Oil Sands
Density RelationshipDensity Relationship
}log = Soo + Sww + (1 – ) Gm
Where:So = oil saturation
Sw = water saturation
log= density from logs
o = density of oil
w = density of water
Gm = matrix density
(1 - )
Intact rock
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Sampling Viscous Oil Sands
Calculate Porosity from Calculate Porosity from LogLog
= Gm - log Gm - Soo - Sww
So, Sw, o, w from core (Sg = 0)
Gm is measured on a grain sample
Then, do quality control assessments
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Sampling Viscous Oil Sands
Quality Control AssessmentsQuality Control Assessments
Obtain So and Sw from log analyses, compare to lab data to decide if saturations are correct Perhaps some water invasion occurred Always assume Sg = 0, but check on logs
Decide which to use When you have lab-derived porosities and
geophysical-derived porosities: Cross plot of the two Examine the data to see what is happening Make decisions…
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Sampling Viscous Oil Sands
Porosity Cross PlotPorosity Cross Plot
0.40
0.38
0.36
0.34
0.32
0.30
0.280.400.380.360.340.320.30
Log
-deri
ved p
oro
sity
Core-derived porosity
“average”error in
Reasonable data, acceptable scatter
“Typical” heavy oil case
Porosity in serious error
Is it valid to apply an “average” correction factor to core data??
Probably not…
Best is to use individual values of log-derived porosity information
Adjust your core data as required
0.28
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Sampling Viscous Oil Sands
Quality ControlQuality Control
X-plots are useful Careful with “average” corrections You can even check using neutron porosity,
but you must be careful! CNL log numbers may be wrong in heavy oils,
which tend to be deficient in hydrogen, as compared to conventional oil correlations
If there is a lot of clay, the CNL data may also be off the mark somewhat (1-2 porosity units)
Get your logging company to help calibrate your field case
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Sampling Viscous Oil Sands
More Methods More Methods
Needle penetrometer for core consistency Use of sonic travel time transducers in the
laboratory as a QC method Visual examination
Extrusion when core is cut and boxed? Extrusion from cut ends in the lab? Core recoveries of 100% always reported? Gas bubbling from core surface, fluids extruding?
And so on…
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Sampling Viscous Oil Sands
““Correcting” the Data - ACorrecting” the Data - A
Clearly, permeability overestimated as well This is considerably harder to correct If you have some oil-free, undamaged core
with similar characteristics in your field Do lab tests on undisturbed specimens (check) Use these to determine k equation
Compare log k values with core values Is there a useful “correction factor”? Can log data be considered reliable enough?
Find some other way to correct E.g. Kozeny-Carman correlation, Archie plot…
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Sampling Viscous Oil Sands
““Correcting” the Data - BCorrecting” the Data - B
Recalculate your reserves, volumes, etc. You can eventually develop a better
empirical log equation to determine porosity, volume factors, etc. directly
Always test out relationships on specimens that are undisturbed (if this is possible)
I used outcrop samples to do this High quality coring may help, but…
Can’t avoid expansion in heavy oil sands Even core plugging at room temp is damaging Nevertheless, do the best possible…
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Sampling Viscous Oil Sands
A Few More Slides…A Few More Slides…
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Sampling Viscous Oil Sands
Index of DisturbanceIndex of Disturbance
logdensity
logdensity
coreDI
A quantitative measure of core disturbance.
e.g.: Dusseault, 1980, used by others, e.g. Settari, et al. (1993) ID = [10.2%, 18.4%]
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Sampling Viscous Oil Sands
I D =
40%
I D =
30%
I D =
20%
I D =
10%
I D =
0%
A neg
ativ
e va
lue
of I D in
dicat
es
poor c
orrela
tion to
the
logs
Index of DisturbanceIndex of Disturbance
Dusseault & van Domselaar (1982) Fig. 2
25
30
35
20
PO
RO
SIT
Y (
%)
- L
ab
ora
tory
40
POROSITY (%) - Geophysical Density Log
ID < 10% Intact or slightly disturbed
10% < ID < 20% Intermediate disturbance
20% < ID < 40% Highly disturbed
40% < ID Disrupted generally
25 30
Suitable
only for q
ualitativ
e or
descriptiv
e purp
oses
Sampl
es s
uita
ble fo
r hig
h-qu
ality
geom
echa
nical
test
s
Sampl
e qu
ality
ade
quat
e fo
r
mos
t pet
roph
ysic
al re
sear
ch
35 40
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Sampling Viscous Oil Sands
IIDD - O - Oldakowski Table 4.3ldakowski Table 4.3
25
30
35
I D =
40%
20
PO
RO
SIT
Y -
Lab
ora
tory
(%
)
40
POROSITY - Geophysical Density Log (%)
I D =
30%
I D =
20%
25 30
I D =
10%
I D =
0%
35 40
Oldakowski (1994)
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Sampling Viscous Oil Sands
Heavy Oil Core DataHeavy Oil Core Data
Weight percent bitumen Mining application
Summation of fluids Grain weight and Total weight Dean-Stark water (sometimes) Dean-Stark bitumen – corrections
Do not correlate with well logs because of the core dilation problem…
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Sampling Viscous Oil Sands
Core PorosityCore Porosityv.v.Log PorosityLog Porosity
“Evaluation of the Alberta Tar Sands”“Evaluation of the Alberta Tar Sands”Sah, Chase, & WellsSah, Chase, & Wells
SPE 5034 (1974)SPE 5034 (1974)
!!
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Sampling Viscous Oil Sands
Low Disturbance SamplesLow Disturbance Samples
Dr. Amin Touhidi-Baghini, PhD thesis (1998)
McMurray sample from river valley outcrop Minimal disturbance: no gas ex-solution Absolute Permeability measured:
at low confining stress during shear failure
Best laboratory data available (to the present time)
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Sampling Viscous Oil Sands
Absolute Absolute PermeabilityPermeability Increase Increase
ref. Touhidi-Baghini (1998) Fig.8.21 & 8.22
-4 -2 0
4
2
6
8 1042 6
1
5
3
Volumetric Strainv (%)
Ka
Mu
ltip
lier
K2 / K
1
Volumetric Strainv (%)-2 0 42 6
Experimental
Kozeny-Carmen
Chardabellas B=2
Chardabellas B=5
1.6x
6x
Vertical core
specimens with an
average porosity of 33.9%
Vertical
Horizontal2.5x
5%Horizontal core
specimens with an
average porosity of 33.7%
5%
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Sampling Viscous Oil Sands
What Has Been Tried?What Has Been Tried?
Pressure core barrels Non-invasive fluids Special core catchers Special freezing during transport Re-stressing before testing And so on and so forth None of these methods has been satisfactory. The best results have been obtained by…
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Sampling Viscous Oil Sands
Best ResultsBest Results
Sampling in a tunnel through an outcrop where gas pressure was depleted
In other outcrops (but Sw is incorrect)
In very shallow boreholes where pgas is low Core barrels of short L, small potential for
radial expansion, + axial restraint Use of analogue materials from outcrops
(e.g. the oil-free outcrops along riverbanks) Intact samples of deep heavy oil UCS sands
is highly problematic. Is it worth doing??
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Sampling Viscous Oil Sands
Then What?Then What?
If “successful” core has been brought to surface… Freeze to dry ice T for transport Keep fully sealed
Prepare test specimens in cold room (-25°C) Do not plug with a fluid (heat–expansion–etc) Slow lathes for trimming to diameter OK Trim ends flat in the lathe as well
Mount specimens while cold, thaw only when under pressure…
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Sampling Viscous Oil Sands
CoringCoring
Only very shallow cores (<100 m) have achieved any reasonable ID values
A specialized, short length core barrel is advised
Internal flush (no radial expansion) Protruding cutting edge (avoid fluid contact) Some method for axial restraint “Rigid” core sleeve Etc.
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Sampling Viscous Oil Sands
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Sampling Viscous Oil Sands
ConclusionsConclusions
Core damage can be a very serious issue Mis-estimation of reserves by 10-15% Over-estimate permeabilities by factor of 2 to 4 And so on…
Geophysical log-derived is best Use lab or log So, Sw?
Calibrated neutron porosity is “OK” Put into place quality control measures on
coring, testing, lab procedures, log analysis Then, just do the best you can…
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