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Oil Recovery from Bakken Shale by Miscible CO2 Injection
Cathy Zhang, Anthony R. Kovscek
5/11/2016
2 0 1 6 S C C S A N N U A L M E E T I N G
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Agenda
Project motivation & objective
Miscible CO2 EOR
Coreflood experiments with tomographic imaging
Simulation of miscible CO2 injection
Future work
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Project Motivation
One of the most productive tight oil plays in North America
› Technically recoverable oil: 7.4 billion STB
Low primary recovery factor: 5 to 10%
› Rapid decline in production after initial peak
EOR is a necessary step to efficiently explore unconventional liquids-
rich reservoirs
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Choice of EOR Technique for Bakken
Reservoir depth: ~9,000 to
10,500 ft (2,743 to 3,200 m)
Oil viscosity: 0.15 – 0.45 cP
@ Reservoir Conditions
Light crude oil from 36 to 48
º API
Reservoir temperature: 150
to 240 ºF
Reservoir pressure: > 4,000
psi Source: Poellitzer, et al., 2009 (SPE 120991)
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Project Objective
Conduct coreflood experiments to quantify recovery potentials of
continuous CO2 drive at miscible conditions
Apply X-ray Computed Tomography (CT) technique to visualize fluid
flow at core level
› Dual-energy scan at 140 keV and 80 keV
Model the CO2 injection process to reproduce experimental results
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Core Sample Specification
1’’ diameter, 2’’ length
Permeability (with oil): 1.8 µd
Average porosity: 7.5%
Pore volume: ~2 mL
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Determination of Miscibility Pressure of CO2 in Dead Bakken Crude @ 38 ºC (~100 ºF)
Oil @ ambient P Oil/CO2 @ 1000 psi Oil/CO2 @ 1100 psi
Oil/CO2 @ 1200 psi Oil/CO2 @ 1300 psi
Typical Bakken Reservoir
Condition:
150 to 240 ºF
> 4,000 psi
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Experimental Plan
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Experimental Set-up
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Oil Recovery: 70%+ of OOIP from Bakken Core
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0 1 2 3 4 5 6 7 8
Rec
ov
ery
Fa
cto
r
PV of CO2 injected
Co-current Injection of CO2
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Subtraction of Oil Images from CO2 Images at High and Low Energy Levels
Rf = 20%
140 keV
80 keV
Rf = 71%
Rf = 20% Rf = 71%
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Compositional Analysis of the Bakken Crude
Model specifications:
› Peng-Robinson EOS with volume correction
› Aromatics and cycloalkanes lumped into C7+
› Expand from C7 to C200 and lump into 5 pseudo-components
› Limited use of non-zero binary interaction coefficients
Regression study with PVT experimental data
› Constant Composition
› Differential Liberation
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Comparison of Saturation Pressure at T= 237 ºF
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Model
Prediction
Experimental
Data%Error
Saturation
Pressure1991.51 psia 1986 psia 0.3
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Comparison of CCE and DLE Data at T= 237 ºF
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Dead Oil Composition from Two-Phase Flash
ComponentMolar Composition
of Live Oil
Molar Composition
of Flashed Liquids
CO2 0.00260 0.00007
N2-CH4 0.25056 0.00196
C2H6 0.11868 0.00846
C3H8 0.09758 0.02461
IC4 - NC4 0.06399 0.04314
IC5 - NC5 0.04029 0.05275
C6 0.03379 0.05922
C7 - C10 0.18346 0.37769
C11 - C13 0.07872 0.16270
C14 - C17 0.06091 0.12592
C18 - C21 0.03244 0.06706
C22+ 0.03696 0.07641
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MCM Pressure of Dead Oil at 38 ºC
Method of Characteristics (Orr): 1069.5 psi
Method of Multiple Mixing Cells (Ahmadi & Johns): 1175.49 psi
Experimental Miscibility: 1200 psi
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Method of
Characteristics
Method of Multiple
Mixing Cells
% Error 12% 2%
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Conclusion
CO2 proves to be a promising EOR agent for light crudes in Bakken
› Production starts after more than 1PV of CO2 injected
› At least 70% of OOIP recovered
Impact of CO2 injection is more pronounced at low-energy-level CT
scans due to contribution of photoelectric absorption
Existence of fractures aids the transport of CO2
Fluid model is capable of producing reasonable representation of PVT
test results
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Future Work
More coreflood experiments to obtain good volumetric data on the
effect of CO2 on oil recovery
For imaging purpose,
› Longer exposure time
› Use photoelectric dopants
Flow simulation in CMG GEM to reproduce the miscible experiments
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Acknowledgement
SUPRI-A Team
Industry Affiliates
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Appendix
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CT Number Comparison with PVI of CO2
2711.5
2712
2712.5
2713
2713.5
2714
1993
1993.2
1993.4
1993.6
1993.8
1994
1994.2
1994.4
1994.6
1994.8
1995
0 1 2 3 4 5 6 7 8
CT
Nu
mb
er @
80k
eV
CT
Nu
mb
er @
140k
eV
PV of CO2 Injected
Changes of Average CT Number with PV of CO2 Injected
140keV
80keV
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CT Number Comparison at High and Low Energy Levels
High Energy Level Low Energy Level
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Theoretical Reconstruction of CT Number Difference at Energy Level of 140 keV
𝐶𝑇 = 1− 𝜙 ∙ 𝐶𝑇𝑟𝑜𝑐𝑘 + 𝜙 ∙ 𝐶𝑇𝑓𝑙𝑢𝑖𝑑 (4)
Δ𝐶𝑇 = 𝜙 ∙ (𝐶𝑇𝑓𝑙𝑢𝑖𝑑 𝑡 − 𝐶𝑇𝑓𝑙𝑢𝑖𝑑 (𝑡 = 0)) (5)
𝐶𝑇𝑓𝑙𝑢𝑖𝑑 𝑡 = 𝑥𝐶𝑂2𝐶𝑇𝐶𝑂2 + (1− 𝑥𝐶𝑂2)𝐶𝑇𝑜𝑖𝑙 (6)
𝐶𝑇𝑓𝑙𝑢𝑖𝑑 𝑡 = 0 = 𝐶𝑇𝑜𝑖𝑙 (7)
𝑥𝐶𝑂2 =𝑅𝑓𝜌𝐶𝑂 2
1−𝑅𝑓 𝜌𝑜𝑖𝑙+𝑅𝑓𝜌𝐶𝑂2 (8)
Density
g/mL
Pure Fluid CT Number
@140keV
CO2 0.616 -335.1
Oil 0.785 -177.4
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Histogram of CT Number Differences: Experimental vs. Theoretical
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CT Number Comparison @ ϕ=7.5%: Theoretical vs. Experimental
-16
-14
-12
-10
-8
-6
-4
-2
0
0% 10% 20% 30% 40% 50% 60% 70% 80%
CT
Nu
mb
er D
iffe
ren
ce
Oil Recovery, %
CT Number Reconstruction @140keV
Theoretical Experimental
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