Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

CHAPTER 5.
GEOMECHANICAL SIMULATION OF CO 2 INJECTION
16
14
12
10
K0=1, γ1=0
τ
8
K0=1
Initial
6
K0=0
K0=1, γ1=βw
4
K0=0, γ1=0
2
0
K0=0, γ1=βw
5 γ1=0 γ1=βw 25 40
σ'n
Figure 5.2: Cartoon showing how the evolution of the Mohr circle is dependent on the stress
path parameters. K 0 controls the change in size of the circle, γ 1 controls how much the circle
translates.
coordinate of the circle will not move, and so stress evolution is limited. When γ 3 = 0, ∆σ ′ 3 = ∆P fl ,
and the movement of the right-hand coordinate will be maximum, with the circle either shrinking
or translating dependent on the size of K 0 . When γ 3 is large, ∆σ ′ 3 = 0, and the right coordinate
of the circle will not move. If K 0 = 1 then the circle will not move, if K 0 is smaller then the circle
will still shrink. The stress path parameters provide a quick way of assessing the stress evolution of
a reservoir. In the following section I will compute the dependence of the stress path parameters on
reservoir geometry and material properties using numerical techniques.
5.3 Numerical modelling
Most geomechanical modelling techniques use one-way coupling only, with pore pressures passed to
the geomechanical model as a load. However, to increase accuracy, models should have a two-way
coupling, where changes in porosity and permeability caused by deformation are returned to update
the fluid flow simulation. This two-way coupling has only recently been developed in the hydrocarbon
industry (e.g., Minkoff et al., 2004), and requires separate simulators to model the fluid flow and the
geomechanical deformation.
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