Enhanced Geothermal System Essay

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4. Enhanced Geothermal Systems (EGS)
In principle, a temperature of 130C could be reached at any location of the planet at a sufficient depth. For instance, temperatures of this level can be found at depths between 5 and 10 km in half of the surface of USA. Based on this fact, enhanced geothermal systems (EGS) aim at utilizing the heat available at high depths by injecting a heat transfer fluid through a well. Although today few geothermal wells are deeper than 3 km given the high drilling costs and the reduced permeability at these depths (Moore & Simmons, 2013), EGS aim at increasing permeability at high depths by using techniques inherited from the oil and gas extraction industries.
Because in most of the regions where the temperature in the subsurface is above 150C the porosity is insufficient to accommodate significant volumes of fluid, it is necessary to enhance the porosity and permeability by hydrofracturing. Once a determined volume of rock has been stimulated, production wells can be drilled into the zone (Ghassemi,
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Sometimes the drilling fluid is absorbed into zones of high permeability. Also, the proppants used in oil and gas applications have problems in EGS because they loose viscosity at the elevated temperatures of EGS. ii) Equipment failure at high temperatures. Although the oil and gas industry has developed technology that operates up to 175C, EGS needs working temperature of 225-250C. this high temperatures affect the integrity of the drilling equipment, the packers (which are used to seal the high permeability zones) and the drilling muds. iii) Controlling the fracture properties and geometry. Knowledge of the likely response of the rock mass to changes in pressure, pumping rate, or fluid properties with enough degree of certainty is today beyond the available

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