Risks Posed by Brines Containing Dissolved CO 2 Ron Falta 1 , Larry Murdoch 1 , and Sally Benson 2 Catherine Rupecht 1 , Lin Zuo 2 , Kirk Ellison 1 , Chris Patterson 1 , Shuangshuang Xie 1 , Miles Atkinson 1 , Laura Daniels 1 , Qi Zheng 1 1 Clemson University 2 Stanford University January 7, 2013 834383 1
CO 2 Density and Solubility with Depth CO2 Phase Density CO2 Solubility 900.00 60.00 800.00 50.00 700.00 600.00 40.00 Solubility, g/l density, g/l 500.00 30.00 400.00 20.00 300.00 200.00 10.00 100.00 0.00 0.00 0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 Depth, feet Depth, feet Calculated using TOUGH2-ECO2N assuming 35 o C and 10,000 mg/l NaCl Risks Posed by Brines Containing Dissolved CO2 2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
The high CO 2 solubility is significant At 3000 ft depth, we get ~50 g/l (50 times more CO 2 than beer!) Brine Density When CO 2 dissolves, the 1020.000 aqueous phase becomes more 1015.000 dense (about 1% here) brine density, g/l brine density with dissolved CO2 Upward flow would require a 1010.000 brine density without dissolved CO2 caprock defect, and an upward 1005.000 hydraulic gradient > density 1000.000 difference 0 1000 2000 3000 4000 5000 depth, feet Calculated using TOUGH2-ECO2N Risks Posed by Brines Containing Dissolved CO2 3 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012 3
The he Di Disso ssolved C CO 2 is is Se Secu cure -- -- Or Is r Is It It? Solubility trapping – CO 2 dissolves in pore water (up to 60 g/l) Density increase favors downward flow of CO 2 saturated brine Upward flow would require a caprock defect, and an upward hydraulic gradient > 1% However, if a CO 2 saturated brine moved upward, the CO 2 would come out of solution (exsolve), leading to a potentially mobile gas phase IPCC, 2005 4 Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Outline Experiments Pore Core Relative permeability Modeling Fault Wells Dissolved and supercritical injection Outcrop Risks Posed by Brines Containing Dissolved CO2 5 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Laboratory Micromodel Study (Zuo, Zhang, Falta, and Benson, AWR, 2013) Binary Thin section image used micrograph for of Mt. micromodel Simon sandstone Micromodel: 530 mD; PV=1.35 uL Risks Posed by Brines Containing Dissolved CO2 6 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
a Micromodel Initially fill micromodel with water saturated with dissolved CO 2 at 90 bars, 45 o C Depressurize at a rate of 10 b bars/hr Images taken at 1 second CO 2 intervals after onset of exsolution at 31 bars CO 2 first starts to flow out at c 23.5 bars, with a CO 2 phase saturation of 56% CO 2 100um Risks Posed by Brines Containing Dissolved CO2 7 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Comparison of Exsolution and Supercritical CO 2 Injection exsolution , 31 bar exsolution , 25 bar exsolution , 18 bar CO 2 injection , 45 bar Risks Posed by Brines Containing Dissolved CO2 8 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Core Scale Experimental Setup Core Holder CT Scanner Dual-pump System Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Core Experiments Mobility of exsolved gas porosity a ( Zuo, Krevor, Falta, and Benson , TIMP, 2012) Fill core with CO 2 saturated water at 124 bar, 50 o C Depressurize to 27 bar at a rate of 12 bars/hr CO 2 phase saturation reaches CO 2 saturation >40%, but very low mobility c No gravity redistribution after 11days. CO 2 is mobile at 3% gas saturation during flood of the same core Risks Posed by Brines Containing Dissolved CO2 10 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Core Experiments Relative permeability Mt. Simon Sandstone (15.7 mD, 23.9 % porosity) Core Flood Relative Permeabilities Exsolution Relative Permeabilities 1 1 0.9 Krw 0.8 0.1 Relative Permeability Relative Permeability Krg 0.7 krw model krw_new 0.6 0.01 krg model krg_new 0.5 krw model 0.4 0.001 krg model 0.3 0.2 0.0001 0.1 0 0.00001 0.5 0.6 0.7 0.8 0.9 1 0.5 0.6 0.7 0.8 0.9 1 Water Saturation Water Saturation CO 2 phase injection CO 2 exsolution from brine Risks Posed by Brines Containing Dissolved CO2 11 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Core Experiments Hysteretic CO 2 phase trapping Core flood experiments where CO 2 saturation was cyclically increased and decreased to Linear Trapping Model measure trapping 1.0 CO 2 saturation was measured 0.9 0.8 by CT scan Residual S CO2 0.7 0.6 0.5 Trapped CO 2 is a linear 0.4 0.3 function of maximum CO 2 y = 0.5x 0.2 saturation 0.1 0.0 0.00 0.20 0.40 0.60 0.80 1.00 Maximum S CO2 Risks Posed by Brines Containing Dissolved CO2 12 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Core Experiments New relative perm model for hysteretic CO 2 phase trapping Hysteric CO2 Relative Permeability 0.10 Berea Sandstone Simple approach: residual saturation a function of maximum k rCO2 saturation 0.05 Continuously update the max residual saturation Allows use of existing relative permeability 0.0 models 0.5 0.6 0.7 0.8 0.9 1.0 ( ) 2 m S w 1 = − ˆ − ˆ k k 1 S 1 S m rg rg max w w − S S = − ˆ w wr S − w 1 S S wr gr Risks Posed by Brines Containing Dissolved CO2 13 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Modeling Open fault model using TOUGH2-ECO2N Ground Surface +200 30m Confining Layer No flow 0 k x = 10 -11 m 2 k z = 10 -12 m 2 Drinking Water Aquifer -100 Open Fault k z = 10 -11 m 2 , 50m wide Confining Layer k x = 10 -15 m 2 k z = 10 -16 m 2 - 700 k x = 10 -11 m 2 k z = 10 -12 m 2 Saline Formation with Dissolved CO2 -800 50.7 g/L CO 2 Model extends 5,000m in either direction Risks Posed by Brines Containing Dissolved CO2 14 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Model using regular core flood relative permeabilities. Time is 30 years. Dissolved CO 2 mass fraction Gas saturation 400 400 XCO2a: 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 SG: 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 200 200 Y Y 0 0 -200 -200 -400 -400 -600 -600 2000 4000 6000 8000 2000 4000 6000 8000 X X Dissolved salt mass fraction 400 Gas phase CO 2 reaches the XNACL: 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 200 DWA, and spreads to the Y boundaries at 5000m within 30 0 years if the drawdown is -200 maintained. -400 -600 2000 4000 6000 8000 Risks Posed by Brines Containing Dissolved CO2 15 X Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Model using exsolution relative permeabilities. Time is 30 years. Dissolved CO 2 mass fraction Gas saturation 400 400 XCO2a: 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 SG: 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 200 200 Y 0 Y 0 -200 -200 -400 -400 -600 -600 2000 4000 6000 8000 2000 4000 6000 8000 X X Dissolved salt mass fraction • Leakage much less using 400 exsolution relative permeability XNACL: 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 200 Y 0 • Related simulations for wells similar -200 • In all cases, CO 2 migration stops -400 when head imbalance is corrected, -600 no runaway effect 2000 4000 6000 8000 X Risks Posed by Brines Containing Dissolved CO2 16 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Modeling CO 2 injection as dissolved or supercritical Q Properties: Formation: 300m thick, 20km x 20 km Typical of deep sandstone Slope: 0.008, 8m/1km Stochastic distribution Hysteretic capillary and rel. Injection rate: 10 kg CO 2 /s for 20 years Monitoring period: 30 years perm functions Risks Posed by Brines Containing Dissolved CO2 17 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Modeling results CO 2 injection as dissolved or supercritical Supercritical Dissolved 1 km Similar areal footprints after injection ~10 km 2 • Supercritical CO 2 moves after injection, increasing area by 50% (14.9 km 2 ) • Dissolved CO 2 sinks after injection, decreasing area contacting caprock (8.9 km 2 ) • Risks Posed by Brines Containing Dissolved CO2 18 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
Conclusions Brine containing dissolved CO 2 can be mobilized upward by modest hydraulic gradients As the carbonated brine is depressurized, the CO 2 comes out of solution (exsolves) throughout the pore space The exsolved CO 2 phase has a very low relative permeability, even at high phase saturations. Exsolution relative permeability function Hysteric relative permeability represented by updating residual saturation in standard models. Simple, fits data well. Upward flow of brines containing dissolved CO 2 stops when the external driving force is removed, no runaway instability seen. Injection of CO 2 as a dissolved phase is likely to have a similar “footprint” to supercritical CO 2 injection, less mobile after injection. Risks Posed by Brines Containing Dissolved CO2 19 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012
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