Survey of Energy Resources 2007
Enhanced Geothermal Systems
Enhanced geothermal systems (EGS) have been defined as engineered reservoirs that have been created to extract heat from low-permeability geothermal resources. They comprise a huge amount of useful heat stored in rocks that are technically accessible but lack the natural permeability necessary for heat extraction. The concept is to drill deep injection wells into hot basement rock that has limited permeability and fluid content. Water is injected at sufficient pressure to ensure fracturing or open existing fractures within the developing reservoir and hot basement rock. A production well that intersects the stimulated fracture system is drilled and water circulated to extract heat from the hot basement rock with improved permeability. Considerable effort has been devoted to the development of EGS, both in the United States and Europe. It has been estimated that with a reasonable investment in R&D, EGS could provide 100 GWe or more of cost-competitive generating capacity in the United States in the next 50 years (The Future of Geothermal Energy, 2006).