Crisman Annual Report 2009 - Harold Vance Department of ...

Thermo-Poroelastic Finite Element Analysis of Rock Deformation and Damage
Introduction
Stress change and permeability variations caused
by rock failure play an important role in geothermal
reservoir development, particularly in understanding
stimulation outcomes and induced seismicity.
Cold water injection causes significant change in
temperature, pore pressure, and thus the stresses
near the wellbore and in the reservoir which, in turn
influence rock permeability.
Permeability (md)
22
20
18
16
14
12
10
8
6
1 sec
10 sec
30 sec
Objectives
In this work, we present the development of a fullycoupled
thermo-poro-mechanical finite element
model with damage mechanics and stress dependent
permeability for simulating rock response to cold
water injection.
4
2
0
1
2
3
r/a
Permeability distributions around the wellbore.
14
4
5
Stress (MPa)
140
120
100
80
60
1.0
0.8
0.6
0.4
Damage
Pore Pressure (MPa)
12
10
8
6
4
1 sec
30 sec
ref-1 sec
ref-30 sec
40
0.2
Stress
20
Damage
0
0.005 0.010 0.015 0.020 0.025 0.030
r/a
Finite element simulations of a triaxial test. Green line: brittle behavior
of strain-stress relationships; red line: damage evolution when stresses
satisfy the failure criterion.
Approach
Both conductive and convective heat transport are
considered in the thermo-poroelastic formulation.
The model is used to perform a series of numerical
experiments to study the influence of cold water
injection on rock damage and permeability
enhancement. The rock damage is reflected in the
alteration of its elastic modulus and permeability.
Accomplishments
The results show that damage propagation is
accompanied by a relaxation of the effective stress
in the damage zone and its concentration in the
intact rock near the interface with the damage zone.
2
0
1
2
Pore pressure distributions around the wellbore. Solid lines represent
pore pressure distributions for damage; Dashed lines give the results for
the reference case with no damage.
Significance
The model provides a tool for the analysis of stress
induced micro-seismicity and fracture propagation
in geothermal and petroleum reservoirs.
CRISMAN INSTITUTE
Project Information
3.1.21 Reservoir Geomechanics: Thermo-Poroelastic
Analysis of Rock Deformation and Damage
Contacts
Ahmad Ghassemi
979.845.2206
ahmad.ghassemi@pe.tamu.edu
3
r/a
4
5
Sang Hoon Lee
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Crisman Annual Report 2009