A giant, future source of green energy |
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The temperature below the ground surface increases by about 30o C per kilometre depth in the earth’s crust. The heat of the subsurface is referred to as geothermal energy. Deep geothermal energy is often denoted hot dry rock (HDR) power and if the permeability of the deep reservoir is improved by e.g. cracking the rock by hydraulic fracturing (water under high pressure), it may be denoted an enhanced geothermal system (EGS). An EGS is one of the few renewable energy sources that can provide continuous base-load power with minimal environmental impact. EGS may be applied for both direct heating (by hot water) and for electricity production.
The high pressure imposed on the rock during hydraulic fracturing may induce small earthquakes, denoted microseismic events. Pressure and temperature changes that are the associated with fluid flow during the production phase of an EGS may also trigger microseismic events. Normally these microseismic events are not felt by humans, however, in certain cases they are, and it is yet another reason to monitor the development of such phenomena. Naturally occurring earthquakes can occur anywhere at any time, and if not controlled by local microseismic monitoring networks in order to distinguish them from induced microseismic activity, public concern may become an effective showstopper for geothermal projects. A first step in the mitigation of large induced seismic events is a proper monitoring of the microseismicity. For such purpose seismic sensors are generally installed in observational boreholes drilled to within a few kilometres depth around the production wells.
Building on the strong national competence in geosciences, advanced drilling and reservoir characterization and management, Norway has a clear opportunity of taking a strong position in the R&D and utilization of HDR/EGS. NORSAR is one of the members of a large Norwegian consortium, formed in 2009, to promote research and development of EGS.
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