( 2011) proposed that ‘EGS comprise the portion of a geothermal resource for which a measureable increase in production over its natural state is or can be attained through mechanical, thermal, and/or chemical stimulation of the reservoir rock. The Australian Geothermal Reporting Code Committee considered EGS as ‘a body of rock containing useful energy, the recoverability of which has been increased by artificial means such as fracturing’ (AGRCC 2010). Co-produced hot water from oil and gas production is included as an unconventional EGS resource type that could be developed in the short term and possibly provide a first step to more classical EGS exploitation’ (MIT et al. EGS would exclude high-grade hydrothermal but include conduction dominated, low permeability resources in sedimentary and basement formations, as well as geopressured, magma and low grade, unproductive hydrothermal resources. For this assessment, this definition has been adapted to include all geothermal resources that are currently not in commercial production and require stimulation or enhancement. The Massachusetts Institute of Technology (MIT) led an interdisciplinary panel which defined EGS as ‘engineered reservoirs that have been created to extract economical amounts of heat from low permeability and/or porosity geothermal resources. Below are four examples of recent EGS definitions in the public domain. Over the years, different definitions of EGS have been proposed, covering a broad variety of rock types, depth, temperature, reservoir permeability and porosity, type of stimulation technique involved, etc. Based on these criteria, the potential electrical power that could be generated might amount to 50 MW e at a net efficiency of 20%.
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( 1974), the most suitable rock type for HDR is granite or other crystalline basement rock temperatures should vary from 150☌ to 500☌ at depths in the order of 5 to 6 km, with an average flow rate over a 10-year reservoir lifetime of 265 l/s, with hydraulic fracturing achieving a contact surface area of approximately 16 km 2, an average thermal capacity of 250 MW th that could be obtained from the surface heat exchanger, and with pressurized water entering at 280☌ and leaving at 65☌.
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Groß Schönebeck and Horstberg, Germany).Īccording to Potter et al. ( 2010) defined the typical geological settings for EGS, varying from igneous (e.g. All of the above usually imply the use of petrothermal systems (Ilyasov et al. Further nomenclature encountered in the literature include stimulated geothermal system, deep heat mining (Häring and Hopkirk 2002 Häring 2007) and deep earth geothermal. The European EGS project at Soultz-sous-Forêts in France is an example of a HWR reservoir (Duchane 1998). 2011) or as hot wet rock (HWR) when it was established that the formations were not completely dry but contained some fluids.
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HDR was also known as hot fractured rock because of either the need to fracture the virtually impermeable formations or the presence of natural fractures in the hot reservoir (Wyborn et al. The concept is described in Potter et al.
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The currently used term ‘enhanced or engineered geothermal system’ (EGS) has its roots in the early 1970s when a team from Los Alamos National Laboratories began the hot dry rock (HDR) project at Fenton Hill (Cummings and Morris 1979 Tester et al.