Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

CHAPTER 5.
GEOMECHANICAL SIMULATION OF CO 2 INJECTION
q
transition from
shear to compaction
shear-enhanced
compaction
shear
tensile
elastic
pure
compaction
pt
p
pc
Figure 5.3: Schematic illustration of the CamClay yield surface in p − q space. At low stresses the
deformation is elastic. At high normal stresses compaction processes occur, while at high shear
stresses brittle failure occurs. The yield surface is defined by the points p t and p c where it meets
the p-axis.
E 0 is a reference Young’s modulus, and A, B, c, e and m are constants to be determined, while ν min
and ν max are the Poisson’s ratio at high and low stresses. In the plastic regime, the plastic strain rate
˙ε p is given by
where Ψ is the plastic potential, defined as
˙ε p =
˙λ
dΨ
dσ
(5.16)
( ) 1/n p −
Ψ(σ, ε) p pc
v = g(θ, p)q + (p − p t ) tan ψ
, (5.17)
p t − p c
where ψ is the dilation angle and ˙λ is a plastic multiplier.
5.3.3 Coupling of fluid-flow and geomechanical simulations
There are a number of methods that might be used to couple together fluid flow and geomechanical
simulation, including full coupling, one-way coupling, explicit coupling and iterative coupling. (Dean
et al., 2003). The fully coupled method involves solving the equations for fluid-flow and geomechanical
deformation simultaneously in the same simulator. This method is the most numerically accurate.
However, it is difficult to implement, and no commercial simulators with this facility currently exist.
As a result, simplifications would have to be made in the fluid and geomechanical equations.
The other 3 methods all use separate fluid-flow and geomechanical simulators, meaning that commercial
finite element fluid-flow and geomechanical deformation codes can be used. The simplest
method is one-way coupling, where the pore pressure and fluid properties computed by the flow
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