enhanced oil recovery with co2 injectionscience.uwaterloo.ca/~mauriced/earth691-duss/co2_general...
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1
Enhanced Oil Recovery with CO2 Injection
Wei Yan and Erling H. StenbyDepartment of Chemical EngineeringTechnical University of Denmark
Contents
Overview
Mechanism of miscibility
Experimental study of gas injection
MMP calculation
Summary
2
Recovery methods
Primary recovery—by depletionSecondary recovery—by water/gas injection for pressure maintenanceTertiary recovery—after primary and secondary
Enhanced Oil Recovery (EOR): “something other than plain water or brine is being injected into the reservoir” (Taber et al., SPE 35385)
EOR methods
A summary by Taber et al.More than 20 methods
3
Trends in EOR with CO2EOR production in the US
The percentage of EOR projects continues to increaseCO2 injection is the only method that has had a continuous increase
CO2 vs. other gases
Supercritical extraction at reservoir conditions
Easier miscibility than N2, flue gas, C1
Cheaper than liquid hydrocarbons
Safer to handle and pressurize than hydrocarbon gases
Reduction of GHG
4
CO2 sequestration + EOR
The biggest barrier for CO2 sequestrationCO2 sequestration cost: 40-60 $/tonCO2 credit: 1-20 $/ton CO2 (?)
EOR can offset the cost and even make it profitableCO2 injected/extra oil produced (mass): 1:1 to 4:1
3:1 is “carbon neutral”Net CO2 storage ratio: 0.17-0.78 tons/barrel oil
CO2 sequestration + EORMaximum permissible cost of carbon dioxide in $/Mscffor the North Sea (Blunt et al., 1993.)
2.50/1.43/0.941.50/0.86/0.570.50/0.29/0.193.7104.50/2.73/1.702.83/1.62/1.071.17/0.67/0.442.269.50/5.43/3.586.17/3.52/2.332.83/1.62/1.07*1.13
302010Mass ratioVolume ratio(Mscf/barrel)
Oil price ($/barrel)Displacement efficiency(CO2/extra oil)
* The three numbers indicate the maximum price for rates of return r = 0/0.1/0.2
A carbon dioxide displacement would be profitable at a 10% rate of return at a gas price of over $3/Mscf (56$/ton).
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Mechanisms of gas injections
Swelling of the oil phase Lowering of oil viscosityReduction of interfacial tension
Misciblility (no interfacial tension for miscible displacements)
Pseudo ternary system for petroleum mixtures
Three components:Light: C1, CO2, N2Intermediate: C2-C6Heavy: C7+
Useful to illustrate basic concepts
Cannot explain combined mechanism
0.00 0.25 0.50 0.75 1.00
Two phase region
C
(0.20,0.55,0.25)
Single phase region
BA3 1
21.00
0.75
0.50
0.25
0.001.00
0.75
0.50
0.25
0.00
Critical tie line
6
First contact miscibility (FCM)
FCMSingle phase at any proportion
Minimum Miscibility Pressure (MMP)
Fix Comp., change PFCM pressure (FCMP)
Minimum Miscibility Enrichment (MME)
Fix P, change Comp.
P'>P
P
Gas A"
Gas A'
Gas A
Oil B
dilution line
3 1
2
FCMP and swelling test
Experimental/modeling determination of FCMP Easy to perform and provide basic information about gas injection
200
250
300
350
400
450
500
550
600
0.00 0.20 0.40 0.60 0.80 1.00Fraction of Gas
Psat
(atm
)
FCMP
Oil Gas
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Multicontact miscibility
Gas and oil become miscible by multiple contacts, through which (one or both of) their compositions are changed.
Easier than FCMFor 1D gas injection, 100% recovery if MCMIn reality, >90% recovery for swept areaThree mechanisms
VaporizingCondensing (No such thing in a real reservoir)Combined (Zick, 1986)
Vaporizing mechanismIntermediate components “vaporize” to gas
Miscibility achieved in the displacement front/far from the well
Dry gas/oil with sufficient intermediate components
G2
3 1
2
critical tie line
C
G1
Gas
Oil
System C1/C4/C10 just above MMP
8
Vaporizing mechanism
Study using slimtube simulation
0.0 0.2 0.4 0.6 0.8 1.00
200
400
600
Gas
Liquid
Gas
sat
urat
ion
ln K
iD
ensi
ty (k
g/m
3 )
Dimensionless distance
-3-2-101
n-Decane
n-Butane
Methane
0.00.20.40.60.81.0
Gas/oil region
Oil regionGas region
Condensing mechanismIntermediate components “condense” to oil
Miscibility achieved in the displacement rear/near from the well
Heavy oil/enriched gas (with sufficient intermediate components)
System C1/C4/C10 just above MMP
C
critical tie line
O2O1
Oil
Gas
3 1
2
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Condensing mechanism
Study using slimtube simulation
0
200
400
600Liquid
Gas
Den
sity
(kg/
m3 )
Dimensionless distance
-3-2-101
n-Decane
n-Butane
Methane
0.00.20.40.60.81.0 Gas/oil
region
Oil regionGas region
ln K
iG
as s
atur
atio
n
Condensing mechanism ?Now it is believed that there is no such mechanism in a real reservoir.
Reason: the multicomponent system (reservoir fluid) contains both light intermediate and heavy intermediate. Gas tends to extract heavy intermediate, leaving the oil saturated with light and light intermediates, which are hard to be miscible with the gas.
The exchange of components is “two-way”, both vaporizing/condensing can happen. This leads to the combined mechanism.
10
Combined mechanism15 comp. (N2, C1, CO2, C2, C3, iC4, nC4, iC5, nC5, C6 and 5 C7+ comps).
0.0 0.2 0.4 0.6 0.8 1.00
200400600800
1000
Gas
sat
urat
ion
ln K
i
Near miscible zone
Vaporizing segment Condensing segment
Gas
Den
sity
(kg/
m3 )
Dimensionless distance
-8-6-4-202
0.00.20.40.60.81.0
Gas region
Gas/oil regionOil region
Liquid
Experimental study
Swelling testEasy to perform
Forward- and backward-contact
Slimtube experiment
Rising bubble apparatus
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Forward contact
Simulate vaporizing processProvide phase and volumetric data for the processMiscibility can be achieved if P>MMP
Oil
GasOil1
Gas1
Removed
…Gas1
Oil
Backward contact
Simulate condensing process
Injection gas
Oil
Injection gas
Oil1
Gas1
Oil1
Removed
…
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Slimtube experimentPhysically simulates gas injection into a 1D reservoir
Standard method to determine MMP
1.2 Pore Volume Injection (PVI) at different pressures
Recoveries measured
Time consuming
Slimtube experiment
MMP is determined as the pressure corresponding to the break point
55
60
65
70
75
80
85
280 300 320 340 360 380 400 420
Pressure (atm)
Rec
over
y %
MMP
13
Rising bubble apparatusQuick but only for vaporizing mechanism
Pressure Gauge
Windowed PressureVessel
“Flat” GlassTube
Gas Bubble
Needle
Air Bath
OIL
GAS
PUMP
MMP calculation methodEmpirical correlations
Limiting tieline method
Single cell simulation
Slimtube simulation (multicell/cell-to-cell simulation)
Global approach by key tieline identification (semi-analytical method based on intersecting tie lines)
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Experimental correlations
Many suggestions found in the literature
Expressed, e.g., as functions of pseudo critical properties of gas, specific gravity of gas…
Easy to use, fast predictions
Accurate for “reference” system
Inaccurate for other systems
Limiting tie line method“Negative” flash to find the P when the injection tie line or the initial tie line become “critical”
Fast, but without stability analysis
only for pure vaporizing /condensing
C1
C2-C6
C7+
•
•Gas
Oil•
Critical point
Initial tie-line
Injection tie-line
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Single cell simulation
Jensen and Michelsen, 1990Correponding to forward/backward contact (vaporizing/condensing mechanisms)
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0 20 40 60 80 100 120 140 160
Number of contacts
LInitial tie-line
Onecell simulation
∑=
−=nc
iii yxL
1
22P < MMP
Multicell (slimtube) simulation
Multicell (cell-to-cell) simulation—physical description
Slimtube simulation—mathematical description
Cell 1 Cell 2 Cell n
Injection gas Production
Batch i
( )nki
nki
nki
nki FF
ztCC 1,,,
1, −+ −
∆∆
−=n = time stepk = grid block
iC
iFOverall molar composition
Overall molar flux
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Assumptions in slimtube simulation
The porous medium is homogenous and incompressible
Instantaneous thermodynamic equilibrium
Small pressure gradient compared to total pressure
Capillary forces and gravity are neglected
The flow is isothermal and linear
Mass transfer by diffusion/dispersion is neglected
Slimtube (multicell) simulation
Directly simulate slimtube experimentGive correct MMP
Time consumingNumerical dispersion if grids are too few
Simulation time proportional to Ngrid2
Extrapolation to infinity Ngrid needed, for example, determine RF∞(P) by plotting RF(P) vs. 1/sqrt(Ngrid) and extrapolating to zero.
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Slimtube simulation (example)
-12
-10
-8
-6
-4
-2
0
2
4
0 100 200 300 400 500
Grid number
ln (K
)
0
0.2
0.4
0.6
0.8
1
1.2
Vap
or m
olef
ract
ion
Recovery curves from slimtubesimulations (numerical dispersion)
0
0.2
0.4
0.6
0.8
1
1.2
100 150 200 250 300 350Pressure (atm)
RF
at 1
.2 P
VI
FD (100 grid blocks, 1200 time steps)FD (500 grid blocks, 6000 time steps)FD (5000 grid blocks, 60000 time steps)
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A MMP calculation method is needed
Can correctly account for the injection mechanismWrong mechanism leads to overestimation
FastUnlike slimtube
No numerical artifacts like numerical dispersion
Global approach by key tielineidentification
Fast, semi-analtyical based on intersecting key tielines
Based on the analysis of 1D multicomponent two-phase dispersion free flow using the Method Of Characteristics (MOC)
0=∂∂
+∂∂
xF
tC ii nci ,..,1=
19
Main results from the analysis (I)In the composition space, the analytical solution forms a composition path starting from the injection gas composition to the initial oil composition.
The composition path must travel through a sequence of key tielines.
For a nc component system, there are nc-1 key tielines, including
The initial tie line and the injection tie linenc-3 crossover tielines
Main results from the analysis (II)At MMP, one of the key tie lines become critical
vaporizing and condensing mechanisms are special cases when the initial key tie line and the injection key tie line become critical
The composition path can have discontinuities known as shocks. When the path consists ONLY of shocks (the usual case), the key tie lines will intersect pairwise.
For other situations (solution consisting of not only shocks but also rarefactions), intersection of key tielinesis a good approximation
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Illustration of the concepts
C10
Initial oilInitial tie line
CH4
Injection tie line Crossover tie line
CO2 Injection gas
C4
Solution path
Semi-analytical 1D Solutions
T,P fixed
nc-1 key tie linesS
z0 1
Details: find intersection key tielines
CO2
C4
C10
True point of intersection
Wang and Orr (1997)
Jessen et al. (1998)
Tie-line extending through injected Gas
Tie-line extending through initial Oil
OilGas
Critical point
21
Details: mathematical models (I) Intersection equations
Isofugacity criterion
⎩⎨⎧
−==
=−1,1
,1 , 0ˆˆ
ncjnci
yx vi
ji
li
ji ϕϕ
( ) 0)1(1 21
212121 =−−−+− +
−−+
jj
ijj
ijj
ijj
i yxyx αααα
1,1 −= nci 2,1 −= ncj
1,1 0)1(
0)1( 11
11
−=⎭⎬⎫
=−−−=−−−
−− nciyxzyxz
injnciInj
nci
Inji
OiliOiliOili
ββββ
Specification of Initial and Injection composition
Details: mathematical models (II)
∑=
−==−nc
i
ji
ji ncjyx
1
1,1 , 0
Summation of mole fractions
Total number of equations
)1(2 2 −= ncNequations
Newton-Raphson iteration scheme.
0 =+∆ FJ
22
Details: structure of Jacobianmatrix (nc=4)
X . . . X . . . X . . . . . . . . . . . . . . . . . . . . .. X . . . X . . X . . . . . . . . . . . . . . . . . . . . .. . X . . . X . X . . . . . . . . . . . . . . . . . . . . .X X X X . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . X X X X . . . . . . . . . . . . . . . . . . . . . .X X X X X X X X . . . . . . . . . . . . . . . . . . . . . .X X X X X X X X . . . . . . . . . . . . . . . . . . . . . .X X X X X X X X . . . . . . . . . . . . . . . . . . . . . .X X X X X X X X . . . . . . . . . . . . . . . . . . . . . .X . . . X . . . . X . . . X . . . X . . . . . . . . . X . .. X . . . X . . . . X . . . X . . X . . . . . . . . . X . .. . X . . . X . . . . X . . . X . X . . . . . . . . . X . .. . . . . . . . . X X X X . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . X X X X . . . . . . . . . . . . .. . . . . . . . . X X X X X X X X . . . . . . . . . . . . .. . . . . . . . . X X X X X X X X . . . . . . . . . . . . .. . . . . . . . . X X X X X X X X . . . . . . . . . . . . .. . . . . . . . . X X X X X X X X . . . . . . . . . . . . .. . . . . . . . . X . . . X . . . . X . . . X . . . X . X .. . . . . . . . . . X . . . X . . . . X . . . X . . X . X .. . . . . . . . . . . X . . . X . . . . X . . . X . X . X .. . . . . . . . . . . . . . . . . . X X X X . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . X X X X . . . .. . . . . . . . . . . . . . . . . . X X X X X X X X . . . .. . . . . . . . . . . . . . . . . . X X X X X X X X . . . .. . . . . . . . . . . . . . . . . . X X X X X X X X . . . .. . . . . . . . . . . . . . . . . . X X X X X X X X . . . .. . . . . . . . . . . . . . . . . . X . . . X . . . . . . X. . . . . . . . . . . . . . . . . . . X . . . X . . . . . X. . . . . . . . . . . . . . . . . . . . X . . . X . . . . X
Details: search for MMPDisplacement of Zick[1] Oil by Gas A
0
0.1
0.2
0.3
0.4
0.5
0.6
120 130 140 150 160
Pressure (atm)
Tie-
line
Leng
th
Displacement of Zick [1] Oil by Gas B
0
0.1
0.2
0.3
0.4
0.5
0.6
120 135 150 165 180 195 210
Pressure (atm)
Tie-
line
Leng
th
Tie-line length equals 0 at MMP( )∑=
−=nc
iii yxd
1
2
23
Details: validation of the algorithm
Method / Oil Zick-A Zick-B SVOC SVOD SVOC+D
Multicell [2] - - 514.2 231.9 310.9
Slimtube [2]* - - 512 ± 7 228 ± 10 302 ± 10
Slimtube [1]** 152 213.8 - - -
Louis Bleriot*** 157 211 524 216 298
Key tie line 156.74 211.0 519.3 217.3 295.7
Time (seconds) 0.7 0.7 1.9 1.7 1.6
Comparison of different results from literature. P (atm)
*Eclipse simulation, ** Experimental, *** Multicell
[1] Zick, 1986; [2] Høier, 1997
Details: validation of the algorithm
150
250
350
450
550
150 250 350 450 550Multicell Simulator MMP (atm)
Cal
cula
ted
MM
P (a
tm)
24
Influence of gas composition on MMP
EyEyy solventgasinj +−= )1(
Gas enrichment study when two gases are availableThe rich gas is treated as solvent
Monotonic Non-monotonic
Extension: semi-analytical solution to 1D two-phase gas injection
Identification of key tielines
1D solution to fullly self-sharpening systems (only of shocks)
1D solution to systems also having rarefactions
3D streamline based compositional reservoir simulation
MOC
MOC
Streamline method
25
Example
0.00
0.20
0.40
0.60
0.80
1.00
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
Wave velocity (z/t)
Vol
ume
fract
ion
of g
as (S
)
MOCNumerical (100,450)Numerical (1000, 4500)Numerical (10000, 45000)
A near miscible displacement at 365 atm and 387.45 K.
0.9 sec
4.4 sec
5.4 min
7.8 hr
Besides phase equilibrium...
Viscosity instabilityCO2 viscosity: 0.02-0.05 cPReservoir fluids: 0.5-5 cPInherently unstable
Gravity segregationCO2 desnity: 1/2-3/4 water density, close to oil
Reservoir heterogeneityChanneling
26
SummaryEOR with CO2 provides double benefits in terms of sequestering CO2 and improving oil recovery
EOR with CO2 injection is mainly attributed to multicontactmiscibility. Three mechanisms for MCM are discussed, only two ofthem (the vaporizing and the combined) are realistic
In experimental study of CO2 injection, swelling test is the easiest one to perform while only the slimtube experiment can correctly determine MMP (also the standard method).
SummaryMany MMP calculation methods are available, but only two (the slimtube simulation and the intersecting tieline method) can capture the correct mechanism. The first one is time consuming and needsextrapolation, while the second one gives quick and correct solution.
A useful extension of the intersecting tie line method is the semi-analytical solution to 1D two-phase gas injection, which can be further used in streamlined based reservoir simulation
MMP (phase equilibrium) only determines local displacement efficiency, sweep efficiency are related to other aspects (viscosity, gravity, rock heterogeneity) which must be taken into consideration.