Enhanced geothermal systems (EGSs) are one among the two reservoir-independent approaches currently being explored by geothermal developers to tap into geothermal energy without relying on natural hydrothermal reservoirs.
EGSs use a combination of methods including hydraulic, thermal and chemical stimulation to drill deep wells and open up or create fractures in the rock. Hydraulic stimulation involves the process of injecting fluids such as water, additives or proppants into underground rock formations to initiate hydraulic fracturing or hydroshear stimulation. In simple words, the high pressure created through these fluid injections causes new fractures to be form or natural fractures to open up. Thermal stimulation on the other hand, involves the induction of thermal shocks by allowing cold fluid to circulate into the hot-rock mass, while chemical stimulation involves dissolving specific minerals and creating voids.
EGS techniques enables geothermal energy to be extracted from regions having high subsurface temperatures but with limited fluid volumes and permeability of natural rock. Hotter temperatures that exist deeper within the impermeable crystalline basement formations could prove advantageous for EGSs with further innovation. Having experienced difficulties in reducing water losses and parasitic loads, the EGS technology remains technically challenging. While flow rate achievements in some notable ongoing projects indicate new experimental ESG approaches, new stimulation methods and adherence to appropriate protocols for seismicity could help resolve some of these challenges.