Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

CHAPTER 4. A COMPARISON OF MICROSEISMIC MONITORING OF FRACTURE STIMULATION DUE TO WATER
VERSUS CO 2 INJECTION
Fluid R P
Water 0.422 99.9%
CO 2 0.124 60.0%
Combined 0.260 99.3%
Table 4.1: Correlation coefficients (R) and statistical significance of correlation (P) for event
magnitudes versus both injection pressure. We consider the data for both fluids separately, and
the overall dataset combined.
−3
Water
CO 2
−3.2
Event Magnitude
−3.4
−3.6
−3.8
P=60.0457%
R=0.1244
P=99.3178%
R=0.26008
P=99.9122%
R=0.42175
−4
−4.2
0 10 20 30 40 50
Pressure (MPa)
Figure 4.11: Event magnitudes as a function of the pressure at the time that the event occurs.
The events during water injection are marked by ’x’, during CO 2 by ’o’. The best-fit
lines (dashed=water, solid=CO 2 , dotted=combined), correlation coefficients, and statistical significances
are all marked.
dip. From Figure 4.12, it appears that the majority of results have ψ orientated horizontally. This is
confirmed in Figure 4.13, which shows a histogram of ψ orientations.
Of the 600 potential splitting measurements (50 events × 12 receivers) available during CO 2
injection, 47 provided class A results. The SWS results are plotted in Figure 4.14, with a histogram
of ψ orientations in Figure 4.15. As during water injection, the majority of results have ψ orientated
subhorizontally.
4.5 Initial S-wave polarisation
It appears that the majority of events recorded during both stages have ψ orientated subhorizontally.
From engineering work done in the reservoir (S.C. Maxwell, pers. comm., 2008), it is believed that the
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