Supercritical CO2 leakage Modeling for Well Integrity in Geological

Storage Project

Houdu E., Meyer V., Poupard O.Oxand S.A., France

COMSOL ConferenceNovember 4-6, 2008

Storage Project

Presented at the COMSOL Conference 2008 Hannover

Outline

� Context

Geological storage project

�OXAND’s activities: Well Integrity Risk Analysis

� Modelling� Modelling

Governing equations

�Porous media flow, biphasic system

� Results

2

Context

� Confirmation of global warming

Kyoto agreement

� CO2 market

legal framework,legal framework,taxes

� EOR

Enhanced Oil Recovery

Growing interest for CO2 geological storage as a feasible and relevant solution

3

Geological storage project

� CO2 Injection and long-term geological storage in:

Hydrocarbon reservoirs

Saline aquifers

Coal-bed

4

Geological & Biosphere system

Hydrocarbonreservoir

Wells

Saline aquifer

5

Geological system

Aquifer

Hydrocarbonreservoir

Caprock

6

Well Integrity Risk Analysis

Aquifer

Hydrocarbonreservoir

Caprock

7

Well Integrity Risk Analysis

Reservoir depletion

8

Well Integrity Risk Analysis

Reservoir depletion

9

Well Integrity Risk Analysis

10

Well Integrity Risk Analysis

CO2 injection

11

Cement sheath

Well Integrity Risk Analysis

CO2 leakage through the well during the injection and at long-term ?

12

< 1 m

1-5 km

Well Integrity Risk Analysis

13

< 1 m

1-5 km

Well Integrity Risk Analysis

14

< 1 m

1-5 km

Well Integrity Risk Analysis

1504/11/2008

Rat hole1-5 m

Rat hole represents key element in the CO2 leakage simulation

15

Modelling

�Biphasic flow model

Water + Supercritical CO2Incompressible phases

�Fluids properties at p, T bottom injection �Fluids properties at p, T bottom injection reservoir

�Well modelling

Well is assumed as a concentric system

�Cylindrical coordinates

16

Meshing

17

Meshing

1818

Computation stage

� Initial condition:

Initial equilibrium

Depletion period

Injection

pw

pnw

Reservoir Pressure

Timedepletionperiod

post injection

� Boundary condition

Aquifer connection� water

Bottom reservoir connection� CO2

Surface connection� atmosphere, water

Initialequilibrium

periodinjection

injection

Aquifer

Surface

Reservoir

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Governing Equations

�Wetting phase:

(1)0)(, =

+∇

⋅−⋅∇+

∂∂

gHpkk

t

Sww

w

wrwS ρ

ηδ

�Non-wetting phase:

(2)

∂t wη

0)(, =

+∇

⋅−⋅∇+

∂∂

gHpkk

t

Snwnw

nw

nwrnwS ρ

ηδ

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Pressure form

�Wetting phase:

(3) 0)()( ,

, =

+∇

⋅−⋅∇+

∂−∂

gHpkk

t

ppC ww

w

wrwnwwp ρ

η

�Non-wetting phase:

(4)

∂t wη

0)()( ,

, =

+∇

⋅−⋅∇+

∂−∂

gHpkk

t

ppC nwnw

nw

nwrwnwnwp ρ

η

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Specific capacity

�Specific capacity

�Relationship between effective water saturation and specific capacity

c

wsnwpwp p

SCC

∂∂=−= δ

,,

saturation and specific capacity

( )m

mmwrwp S

m

mC

Θ−Θ−

−=

11

,, 111

φα

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Porous media

� Capillary pressure

� Relationship to close biphasic flow model (Van Genuchten):

wnwc ppp −=

M(Van Genuchten):

(7)

the effective saturation of wetting phase

the capillary pressure pcthe capillary pressure head pec

Θ=

+ 1

1

MN

ec

c

p

p

rw

rww

S

SS

−−

=Θ1

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Main Results: Effective Water Saturation

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Main Results: Effective Water Saturation

Max: 1

Min: 0.125

Effective Water Saturation

Casing

Sew max = 1

Caprock

Reservoir

Sew min = 0.15

No CO2 leakage with aquifer connection26

Effective Water Saturation

Casing

Sew max = 1

Caprock

Reservoir

Sew min = 0.15

No CO2 leakage with aquifer connection27

Radial pneumatic gradient

Casing

0>∂Hnw

Caprock

Reservoir

0>∂

∂r

Hnw

No possible CO2 radial flow in the rat hole

0<∂

∂r

H nw

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Numerical difficulties

� Space distortion

Radial size scale: <1 m

Axial size scale: 1000 m

� Permeability

Well cavity (5O D)

Caprock ( 0.001 mD)Caprock ( 0.001 mD)

Bad cement sheath (10 mD)

���� Large ranges of values for parameters describing the well induce numerical difficulties

� Capillary pressure head

Need values > 0,1 bar to converge

���� Due to Van Genuchten model

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Conclusions

� Numerical simulations have highlighted the competition between the gas flow and the liquid flow in a specific area of a well

� The rat-hole zone constitutes a key element to consider in the long term integrity performance of a wellwell

� An improvement of the knowledge of the flows in this specific area within the well will be a support in assessing the Performance and the Risks from a well integrity perspective

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Future works

� Robustness analysis to be performedTo quantify the CO2 leakage in the case of no aquifer protectionImprovements in the modeling to take into account the significant differences between some parameters values for two linked elementsvalues for two linked elements

� This study will have to be coupled to a macroscopic CO2 leakage modelling within well system.

Essential into a quantitative well integrity risk analysis for CO2 storage projects

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