Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

CHAPTER 5.
GEOMECHANICAL SIMULATION OF CO 2 INJECTION
80
80
σ 3
(MPa)
σ 3
(MPa)
75
70
Stiff
65
Med
Soft
60
0 5 10 15
∆P (MPa) fl
80
75
70
65
60
0 5 10 15
∆P fl
(MPa)
σ 3
(MPa)
σ 3
(MPa)
75
70
65
60
0 5 10 15
∆P (MPa) fl
80
75
70
65
60
0 5 10 15
∆P fl
(MPa)
(a)
σ 3
(MPa)
σ 3
(MPa)
80
75
70
65
60
0 5 10 15
∆P fl
(MPa)
80
75
70
65
60
0 5 10 15
∆P fl
(MPa)
(c)
(b)
Figure 5.10: Changes in vertical stress in the overburden (upper panels) and sideburden (lower
panels) with pore pressure increase in the reservoir. The flat, extensive reservoir (1z:100x:100y)
is shown in (a), the long thin case (1z:100x:5y) is in (b) and the short fat case (1z:5x:5y) is in (c).
The different coloured lines show the results for the different stiffness reservoirs.
In Figure 5.10 I plot the changes in vertical stress σ 3 in the over- and sideburden as a function of
the pore pressure change at the centre of the reservoir. I note that in the overburden σ 3 increases for
the smaller reservoirs, and especially so when the reservoir:overburden stiffness ratio is small. Above
the extensive reservoir there is little stress change. In the sideburden of the smaller reservoirs σ 3
decreases, and again this effect is most pronounced for the softer reservoirs. There is also some stress
evolution in the sideburden of the softest extensive reservoir, but this change is less than for the
smaller reservoirs.
5.4.1 Stress arching
The stress evolution can be interpreted within the framework of stress arching. Stress arching is
commonly observed during reservoir production (e.g., Hatchell and Bourne, 2005). As the reservoir
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