Hot Dry Rock & Enhanced Geothermal System |
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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 and may be regarded as a result of heat flow from the earth’s core and mantle and heat production from the decay of radioactive isotopes (locally) in the rocks of the crust. 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. Reactive flow in a reservoir, such as solution and precipitation of minerals (scaling) can have a strong impact on the permeability of a reservoir in the long run, and might be responsible for changes in the fluid flow and reactivation of faults. Changes in the fluid flow may have crucial impact on the economics of a geothermal site and it is important to monitor geothermal reservoirs throughout its lifetime to improve the understanding of induced seismicity associated with geothermal power. 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.
NORSAR is involved on a regional level with Akershus University College and the power company Akershus Energi AS to provide an educational platform (at the MSc level) for environmentally friendly energy where geothermal energy will constitute one of several options for education and research on renewable energies.
Active projects
Pre-study for a demonstration and pilot-project within geothermal energy at the Akershus EnergiPark (Akershus EnergyPark)
The main objective of the pre-study is to screen the existing international knowledge about geothermal energy research and to prepare a proposal for a feasibility study. An important sub-goal is to identify the most competent partners and to evaluate challenges, costs, and risks for Enhanced Geothermal Systems.
Duration: June - October 2009
Participants: NORSAR
Financing: Energi - energieffektivisering - miljø (FEM)
Project leader/Contact: Volker Oye, NORSAR, Gunnar Randers vei 15, 2007 Kjeller
GEISER - Geothermal Engineering Integrating Mitigation of Induced Seismicity in Reservoirs
The project contributes to the improvement of the concept of Enhanced Geothermal Systems by investigating the role of induced seismicity.
Duration: 2010-2013
Participants: GFZ, BRGM, ISOR, TNO, ETH, StatoilHydro, Geowatt, NORSAR, Armines, EOST, KNMI, AMRA, INGV
Financing: EU FP7
Project leader/Contact: GFZ, Dr. Ernst Huenges, Dr. David Bruhn
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