Wednesday, 24 February
Victorian Minister says "Yes" to Geothermal Energy Meeting
Geelong
Advertiser reported last week that the Victorian Energy and Resources Minister
Peter Batchelor has agreed to meet disgruntled Gherang residents. Some residents
are apparently concerned about the potential earthquake risk presented by the
Greenearth Energy project in the area.
The concerns are probably caused by a number of news reports coming from overseas
last several months following the termination of the Basel project in Switzerland
and the Altarock project in California. This shows the importance of public
perception. The Greenearth Project is a HSA(Hot Sedimentary Aquifer) project
that relies on the natural permeability of the reservoir. As far as I know,
no reservoir stimulation is planned for HSA projects and Greenearth web site
confirms that they will be no exception. I quote from the Company
Announcement on 5 February:
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From Greenearth Announcement:
Q: Will the geothermal investigations cause seismic activity?
A: No. Seismic activity is in no way associated with the extraction
method used to access the hot water in the hot sedimentary aquifers being
targeted by Greenearth Energy. As the sedimentary materials targeted are
naturally permeable (similar to the shallow aquifers providing borehole
water) they do not need to be fractured or shattered. The reported seismic
event that occurred in Switzerland, and which has caused some community
concern, was the result of an entirely different process that requires
hard granite hot rocks to be fractured to allow water to flow through
the rocks. It is alleged that this process led to, we understand, the
reported seismic activity. This technique of hard hot rock fracturing
is not used to extract geothermal fluids from hot sedimentary aquifers
being investigated by Greenearth Energy.
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The following image shows the utilisation of a Hot Sedimentary Aquifer (HSA).
I think the image is from a past Panax presentation but the technology is similar
to the Greenearth project near Geelong.
The assumed attraction of the HSA projects comes from the fact that the reservoir
is permeable. There is no need to stimulate fracture in permeable reservoirs
and therefore there is no earthquake risk.
This does not mean that the EGS is risky. It is important to note that even
with the EGS projects that caaused the newspaper reports from basel and USA,
the magnitude of the surface seismic events has been small (about 3 on the Richter
scale) and this should be no cause for concern especially in geologically stable
areas like all of Australia.
Nevertheless, public perception is important and if there is concern in Australia
associated with the seismic risk from geothermal projects, Australian geothermal
industry should recognise this and try to address such concerns through various
means. I do not know what these means can be but, for example, it probably would
help making public the surface seismic recordings taken during stimulation of
EGS reservoirs and comparing them against other recordings obtained during publicly
accepted practices such as underground mine blasting, petroleum and gas hydrofracturing,
tunnel development in the cities, etc. Similar can be done during the HSA operation
even though we do not expect any significant seismicity high enough to be measureable
on the surface.
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