Risks Posed by Brines Containing Dissolved CO 2 Ron Falta 1 , Larry - - PDF document

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Risks Posed by Brines Containing Dissolved CO 2 Ron Falta 1 , Larry - - PDF document

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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

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Ron Falta1, Larry Murdoch1, and Sally Benson2

Catherine Rupecht1, Lin Zuo2, Kirk Ellison1, Chris Patterson1, Shuangshuang Xie1, Miles Atkinson1, Laura Daniels1, Qi Zheng1

1Clemson University 2Stanford University

January 7, 2013

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834383

Risks Posed by Brines Containing Dissolved CO2

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

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CO2 Density and Solubility with Depth

Calculated using TOUGH2-ECO2N assuming 35o C and 10,000 mg/l NaCl

0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00 900.00 1000 2000 3000 4000 5000 density, g/l Depth, feet

CO2 Phase Density

0.00 10.00 20.00 30.00 40.00 50.00 60.00 1000 2000 3000 4000 5000 Solubility, g/l Depth, feet

CO2 Solubility

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

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The high CO2 solubility is significant

 At 3000 ft depth, we get ~50 g/l

(50 times more CO2 than beer!)

 When CO2 dissolves, the

aqueous phase becomes more dense (about 1% here)

 Upward flow would require a

caprock defect, and an upward hydraulic gradient > density difference

1000.000 1005.000 1010.000 1015.000 1020.000 1000 2000 3000 4000 5000 brine density, g/l depth, feet

Brine Density

brine density with dissolved CO2 brine density without dissolved CO2

Calculated using TOUGH2-ECO2N

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

The he Di Disso ssolved C CO2 is is Se Secu cure --

  • - Or Is

r Is It It?

 Solubility trapping – CO2

dissolves in pore water (up to 60 g/l)

 Density increase favors

downward flow of CO2 saturated brine

 Upward flow would require a

caprock defect, and an upward hydraulic gradient > 1%

 However, if a CO2 saturated

brine moved upward, the CO2 would come out of solution (exsolve), leading to a potentially mobile gas phase

IPCC, 2005

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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

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

Laboratory Micromodel Study

(Zuo, Zhang, Falta, and Benson, AWR, 2013)

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Thin section micrograph

  • f Mt.

Simon sandstone Binary image used for micromodel Micromodel: 530 mD; PV=1.35 uL

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

Micromodel

 Initially fill micromodel with

water saturated with dissolved CO2 at 90 bars, 45 oC

 Depressurize at a rate of 10

bars/hr

 Images taken at 1 second

intervals after onset of exsolution at 31 bars

 CO2 first starts to flow out at

23.5 bars, with a CO2 phase saturation of 56%

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a b CO2 c

100um

CO2

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

Comparison of Exsolution and Supercritical CO2 Injection

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exsolution, 31 bar CO2 injection, 45 bar exsolution, 18 bar exsolution, 25 bar

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

Core Scale Experimental Setup

Core Holder CT Scanner Dual-pump System

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

Core Experiments

Mobility of exsolved gas

(Zuo, Krevor, Falta, and Benson, TIMP, 2012)

 Fill core with CO2 saturated

water at 124 bar, 50 oC

 Depressurize to 27 bar at a

rate of 12 bars/hr

 CO2 phase saturation reaches

>40%, but very low mobility

 No gravity redistribution after

11days.

 CO2 is mobile at 3% gas

saturation during flood of the same core

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a

CO2 saturation porosity

c

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

  • Mt. Simon Sandstone (15.7 mD, 23.9 % porosity)

CO2 phase injection CO2 exsolution from brine

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0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.5 0.6 0.7 0.8 0.9 1

Relative Permeability Water Saturation

Core Flood Relative Permeabilities

Krw Krg krw model krg model 0.00001 0.0001 0.001 0.01 0.1 1 0.5 0.6 0.7 0.8 0.9 1

Relative Permeability Water Saturation

Exsolution Relative Permeabilities

krw_new krg_new krw model krg model

Core Experiments

Relative permeability

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

 Core flood experiments where

CO2 saturation was cyclically increased and decreased to measure trapping

 CO2 saturation was measured

by CT scan

 Trapped CO2 is a linear

function of maximum CO2 saturation

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y = 0.5x

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.00 0.20 0.40 0.60 0.80 1.00

Residual SCO2 Maximum SCO2 Linear Trapping Model

Core Experiments

Hysteretic CO2 phase trapping

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

 Simple approach:

residual saturation a function of maximum saturation

 Continuously update

the max residual saturation

 Allows use of existing

relative permeability models

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Core Experiments

New relative perm model for hysteretic CO2 phase trapping

0.5 0.6 0.7 0.8 0.9 1.0

0.10 0.05 0.0

Sw

krCO2

( )

2 1 max

ˆ ˆ 1 1

m m rg rg w w

k k S S = − −

ˆ 1

w wr w wr gr

S S S S S − = − −

Hysteric CO2 Relative Permeability Berea Sandstone

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

Modeling

Open fault model using TOUGH2-ECO2N

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Drinking Water Aquifer Confining Layer Saline Formation with Dissolved CO2 Ground Surface Confining Layer Open Fault +200

  • 100
  • 700
  • 800

Model extends 5,000m in either direction kx = 10-11 m2 kz = 10-12 m2 kx = 10-11 m2 kz = 10-12 m2 kz = 10-11 m2, 50m wide kx = 10-15 m2 kz = 10-16 m2 No flow 50.7 g/L CO2 30m

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

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X Y

2000 4000 6000 8000

  • 600
  • 400
  • 200

200 400

SG: 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

X Y

2000 4000 6000 8000

  • 600
  • 400
  • 200

200 400

XNACL: 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009

X Y

2000 4000 6000 8000

  • 600
  • 400
  • 200

200 400

XCO2a: 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045

Model using regular core flood relative permeabilities. Time is 30 years.

Gas saturation Dissolved CO2 mass fraction Dissolved salt mass fraction

Gas phase CO2 reaches the DWA, and spreads to the boundaries at 5000m within 30 years if the drawdown is maintained.

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

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Model using exsolution relative permeabilities. Time is 30 years.

Gas saturation Dissolved CO2 mass fraction Dissolved salt mass fraction

X Y

2000 4000 6000 8000

  • 600
  • 400
  • 200

200 400

SG: 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

X Y

2000 4000 6000 8000

  • 600
  • 400
  • 200

200 400

XCO2a: 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045

X Y

2000 4000 6000 8000

  • 600
  • 400
  • 200

200 400

XNACL: 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009

  • Leakage much less using

exsolution relative permeability

  • Related simulations for wells similar
  • In all cases, CO2 migration stops

when head imbalance is corrected, no runaway effect

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

Modeling

CO2 injection as dissolved or supercritical

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Formation: 300m thick, 20km x 20 km Slope: 0.008, 8m/1km Injection rate: 10 kg CO2/s for 20 years Monitoring period: 30 years Properties: Typical of deep sandstone Stochastic distribution Hysteretic capillary and rel. perm functions

Q

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

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1 km

Supercritical Dissolved

  • Similar areal footprints after injection ~10 km2
  • Supercritical CO2 moves after injection, increasing area by 50% (14.9 km2)
  • Dissolved CO2 sinks after injection, decreasing area contacting caprock (8.9 km2)

Modeling results

CO2 injection as dissolved or supercritical

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Risks Posed by Brines Containing Dissolved CO2 Falta, Murdoch, Benson, USEPA STAR Progress Review 7 Jan 2012

Conclusions

 Brine containing dissolved CO2 can be mobilized upward by

modest hydraulic gradients

 As the carbonated brine is depressurized, the CO2 comes out of

solution (exsolves) throughout the pore space

 The exsolved CO2 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 CO2 stops when the

external driving force is removed, no runaway instability seen.

 Injection of CO2 as a dissolved phase is likely to have a similar

“footprint” to supercritical CO2 injection, less mobile after injection.

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