Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

CHAPTER 8.
LINKING GEOMECHANICAL MODELLING AND MICROSEISMIC OBSERVATIONS AT WEYBURN
Unit χ ϕ f
Caprock 5 (18.5) MPa 45 ◦
Reservoir 3.5 MPa 40 ◦
Table 8.4: Yield envelope parameters for the Weyburn model. A lower value than that measured
on core samples is used for the cohesion of the caprock, which is given in brackets.
3 months of injection (timestep 12) and after 1 year of injection (timestep 16), both in the reservoir
(Figure 8.7) and in the overburden (Figure 8.8). From these figures I note that fracture potential
increases in the reservoir during production, while it is relatively unchanged in the overburden. Once
injection begins, there is a sharp increase in fracture potential in the overburden above the injection
wells, while there is a drop in fracture potential in the reservoir at the injection well. The fracture
potentials at the producing wells are relatively unchanged during injection.
In general, there are some qualitative comparisons that can be made between this model and
the observations made at Weyburn. For instance, the fact that across most of the reservoir fracture
potential is not increased by injection matches with the lack of seismicity recorded. Also, this model
suggests that fracture potential should be higher at the production wells than at the injection wells,
which matches the observations that the majority of events occur close to the producers. However,
this model can not explain why so many events are located in the overburden above the producing
wells, while the models predict that there should be microseismicity above the injection well, where
none is observed. The suitability of this model can also be assessed through a comparison of the
seismic anisotropy that it predicts.
2000
17
2000
18
1500
16
1500
17.8
15
17.6
Y
1000
Y
1000
14
17.4
500
13
500
17.2
0
1500 2000 2500 3000
X
12
0
1500 2000 2500 3000
X
17
(a)
(b)
Figure 8.5: Map view of vertical effective stress in (a) the reservoir and (b) the overburden of
the Weyburn model at the end of 1 year of CO 2 injection. The horizontal producers and vertical
injectors are marked by lines and triangles respectively. Contours are in MPa.
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