Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

9.1. NOVEL CONTRIBUTIONS
techniques are best for each particular circumstance. For this reason I anticipate that microseismic
monitoring will be deployed in many future CCS projects.
9.1 Novel Contributions
This thesis contributes several novel ideas to the fields of microseismic monitoring, rock physics and
geomechanical modelling, demonstrated using previously unpublished datasets. In particular, the
direct inversion of splitting measurements for fracture properties outlined in Chapter 3 represents an
important development on the standard practise of assuming that shear wave fast direction corresponds
directly to fracture strike. Instead, the inversion procedure allows the effects of sedimentary fabrics
and/or dual fracture sets to be imaged, while the use of synthetic tests allows the error limits imposed
by event distributions to be computed.
The amount of microseismic activity to be expected during CO 2 injection is not only poorly
known, but the issue is rarely raised in CCS literature. Though not directly applicable to Weyburn,
the comparison of hydraulic fractures using CO 2 and water shown in Chapter 4 provides a useful
contribution in this area, and will hopefully stimulate further research regarding this issue.
Rock physics models do exist to map geomechanical deformation to changes in seismic properties
(e.g., Hatchell and Bourne, 2005; Prioul et al., 2004; Zatsepin and Crampin, 1997). However, these
models are sometimes limited in their application (Hatchell and Bourne, 2005), and do not explain
what is happening at microscale levels (Hatchell and Bourne, 2005; Prioul et al., 2004), or are rarely
used because of difficulties in calibrating the models (Prioul et al., 2004; Zatsepin and Crampin,
1997), or because they are difficult to apply (Zatsepin and Crampin, 1997). The rock physics model
developed in Chapter 6 is simple in its application, and yet it models observed nonlinear effects and
stress-induced anisotropy. Furthermore, the model has its basis in observable microscale features of
the rock matrix. The model is easy to calibrate, and I have done so with over 200 core samples
of varying lithology. These advantages have already lead to considerable interest from within the
hydrocarbon industry.
In Chapter 8 I apply a workflow to go from geomechanical modelling to making predictions about
seismic properties (microseismic activity in this case), and comparing these predictions with observations
made at Weyburn, using these comparisons to inform and update the geomechanical model.
Although geomechanical models have previously been used in combination with rock physics to predict
seismic properties (generally using the models cited above, e.g., Minkoff et al., 2004; Hatchell and
Bourne, 2005; Herwanger and Horne, 2005), I am unaware of any models that make comparisons with
microseismic data. This is significant in that microseismic data is an important and easily monitored
indicator of geomechanical deformation. Furthermore, none of the papers cited above have used the
seismic observations to inform the geomechanical models. By identifying the discrepancies between
initial models and observation, I am able to construct geomechanical models that provide a better
match with seismic observations. This process represents an important step in demonstrating the
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