Ran Qi, Valcir T Beraldo, Tara C LaForce, Martin J Blunt

Design of CO2 storage in aquifers

17th Jan. 2008 Imperial College Consortium on Pore-Scale Modelling Project Meeting

SPE-109905

Outline

Background

Objectives

Streamline method for CO2 transport

Simulation results

Conclusions

Future work

SPE-109905Mobile CO2 saturation

Z

170m

X3200m

Y

2280m

Trapped CO2 saturation

X3200m

Y

2280m

Z

170m

Background

Carbon Capture and Storage (CCS)

736 Gt in North Sea alone (DTI) ≈CO2 produced by all UK population for 100 years!!! SPE-109905

Long-term fate

How can you be sure that the CO2 stays underground?

Objectives

Understanding of physical process of CO2 storage, especially trapping, in aquifers and oil fields

• Extend streamline-based simulator

• Apply results from pore-scale modeling

General design of injection strategy

• Aquifers - maximize CO2 storage

SPE-109905

Overview of the streamline method

Permeability field

Initial saturation

Pressure solve

SL tracing

Saturation along SL

Saturation for the next

time stepSPE-109905

Streamline method for CO2 transport

Hydrocarbon phase Aqueous phase

Todd&Longstaff

Fingering model for CO2 in oilSPE-109905

Phases (3) Components (4)

Hydrocarbon

Aqueous

Solid

CO2

Oil

Water Salt

+

+

+

+

+

+

+

+

+

Streamline method for CO2 transport

•Chemical reaction1D vertical discretization

•Gravity solution •Dissolution

KD: Spycher et al (2003, 2005)

SPE-109905

Streamline method for CO2 transport

Trapping model

Pore-scale model matches experimental data.• Kr is from Berea sandstone, which matches Oak (1990)’s

experiments.• CO2/water system is weakly water-wet (Chiquet et al., 2007)

contact angle (θ) = 65º.

New trapping model (Juanes et al., 2006)

2maxmaxgggt SSS

))((4

)1(1

2

1max

2

gggtggtggf

SSSSSSS

SPE-109905

Design of carbon dioxide storage

The ratio of the mobility of injected brine and CO2 to the formation brine as a function of the injected CO2-phase volume fraction, fgi.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

S g

f g

Series1

fgi=0.85Sgi=0.26

fgi=0.5Sgi=0.19

f gi = 0.5

Sgi = 0.190

f g

f gi = 0.85

Sgi = 0.295

The CO2-phase fractional flow fg as a function of CO2 (gas) saturation, Sg.

SPE-109905

0.01

0.1

1

10

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

f ci

Mob

ility

rat

io

Mobility ratio between carbon dioxide/brine mixture and formation brine

Mobility ratio between chase brine and carbon dioxide/brine mixture during chase brine injection

Mobility ratio = 1.0

fgi

Design of carbon dioxide storage

1D analysis: Numerical simulation vs. analytical solution

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 200 400 600 800 1000 1200 1400

Distance (m)

Sg

Simulation

Analyticalsolution

Trapped CO2 Mobile CO2

Dissolution front

Advancing CO 2 front

Chase brine front

fgi = 0.5

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 200 400 600 800 1000 1200 1400

Distance (m)

Sg

Simulation

Analytical solution

Trapped

CO2

Mobile CO2

Dissolution front

Advancing CO 2 front

Chasebrine front

fgi = 0.85

SPE-109905

Design of carbon dioxide storage

Mobile CO2 saturation

Z

170m

X3200m

Y

2280m

Trapped CO2 saturation

X3200m

Y

2280m

Z

170m

Injector

Producer

SPE 10 reservoir model, 1,200,000 grid cells (60X220X85), 7.8 Mt CO2 injected.

Two years after chase water injection for fgi=0.85.

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Design of carbon dioxide storage

3D simulation: Storage efficiency vs. trapping efficiency

Storage efficiency =

the fraction of the reservoir pore volume filled with CO2

Trapping efficiency =

the fraction of the injected mass of CO2 that is either trapped or dissolved

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The storage efficiency is highest for fgi = 0.85, which also requires minimum mass of chase brine to trap 95% of CO2.

0.1

0.3

0.5

0.7

0.9

1.1

1.3

1.5

1.7

1.9

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

f ci

Rat

io o

f the

mas

s of

bri

ne in

ject

ed

to th

e m

ass

of C

O2

inje

cted

0.02

0.021

0.022

0.023

0.024

0.025

0.026

0.027

0.028

Sto

rage

eff

icie

ncy

Storage efficiency

Ratio of the mass of chase

brine injected to the mass of CO 2

Ratio of the total mass of brine injected to the mass of CO 2

Trapping efficiency

90% 95%

Mass ratio

fgi

Design Criterion

• Inject CO2+brine where mobility ratio = 1.0

(fgi=0.85 in this example).

• Inject chase brine that is 25% of the initially injected CO2 mass.

• 90-95% of the CO2 is trapped.

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Conclusions

• Streamline-based simulator has been extended to model CO2 storage in aquifers and oil reservoir by incorporating a Todd-Longstaff model, equilibrium transfer between phases (dissolution) and rate-limited reaction;

• Trapping is an important mechanism to store CO2 as an immobile phase. Our study showed that WAG CO2 injection into aquifer can trap more than 90% of the CO2 injected;

• We have proposed a design strategy for CO2 storage in aquifers, in which CO2 and formation brine are injected simultaneously followed by chase brine.

• Streamline-based simulation combined with pore-scale network modeling can capture both the large-scale heterogeneity of the reservoir and the pore-scale effects of trapping.

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Future work

Injection strategy design

• Field scale simulation using a combination of this extended streamline-based simulator and pore-scale modeling.

• Require better experimental data, since the trapping model used has a significant impact on the results.

• Design of an injection strategy to maximize CO2 storage and oil recovery.

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Acknowledgement

Schlumberger – Faculty for the Future

SHELL – Shell-Imperial Grand Challenge on Clean Fossil Fuels

Thank you!

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