Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

CHAPTER 9.
CONCLUSIONS
accuracy of a particular model, which will be useful for any reservoir activity but particularly for
proving the integrity of a CCS site to the satisfaction of any regulator.
9.2 Future Work
If CCS is to be used a tool for reducing anthropogenic CO 2 emissions by a significant amount then
the current pilot scale projects must be scaled up both in terms of the size of each project and the
number of projects. As such, the lessons learnt during this scale-up will inevitably add a huge amount
of understanding to what we have gained from the pilot projects. Therefore it is likely that there will
be a huge amount of development moving forward some of the ideas presented in this thesis.
This thesis presents a workflow to match geomechanical modelling predictions with microseismic
activity in order to improve our understanding of deformation in reservoirs. This workflow consists of
a number of separate steps, bringing together a number of different disciplines, and improvements in
all of them are likely to be developed in the near future.
The event locations presented in this thesis have been computed by ray-tracing through 1-D
velocity models blocked from borehole logs. Already, new techniques are being developed where the
velocity model is inverted for in combination with the event locations, providing more accurate event
locations and improved velocity models. Additionally, velocity models used for event location are
usually isotropic, yet shear wave splitting observations show that anisotropic models would often be
more appropriate. Multiplet analysis and/or reverse time migration have also shown potential to
reduce the error in event location. With improved event locations, our interpretations of microseismic
activity will be improved.
Although semi-automated, the shear wave splitting measurements that I make have been picked
manually, and the quality control is also done manually. This is possible because there is only a small
amount of data. With larger datasets, these steps must be automated, and techniques are currently
being developed that can do so (e.g., Wüstefeld et al., 2010a). This technique also identifies null
results automatically, which can be important in determining the orientation of anisotropic symmetry
axes.
The geomechanical models developed are simple and representative in nature. I anticipate that,
with greater computing power, full models will be developed with increasing regularity that will allow
the reservoir to be modelled in more detail. However, this greater detail must be accompanied by
more accurate model population. The elastic stiffness across a reservoir unit will not be uniform,
but variable throughout, and this variation could potentially be included if the information could be
inverted for based on high quality 3-D seismic observations or based on geostatistical models that
describe characteristic scales and distributions of heterogeneity. Additionally, it is known that CO 2
will react with the minerals of reservoir rocks, with dissolution of calcite being the principal effect.
With improvements in experimental measurement and reactive transport modelling, the effects of
dissolution on rock mechanical properties might also be included.
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