Abstract
Enhanced (or engineered) geothermal systems (EGS) have evolved from the hot dry rock concept, implemented for the first time at Fenton Hill in 1977. This paper systematically reviews all of the EGS projects worldwide, based on the information available in the public domain. The projects are classified by country, reservoir type, depth, reservoir temperature, stimulation methods, associated seismicity, plant capacity and current status. Thirty five years on from the first EGS implementation, the geothermal community can benefit from the lessons learnt and take a more objective approach to the pros and cons of ‘conventional’ EGS systems.
Highlights
Enhanced geothermal systems (EGS) have evolved from the hot dry rock concept, implemented for the first time at Fenton Hill in 1977
From the information provided in the tables and the plots shown earlier, it appears that engineered geothermal system’ (EGS) projects currently under development are still on the learning curve, overcoming problems, gaining experience and trying to introduce advanced technology; the projects already concluded provide relevant history and analogy for upcoming developments and the projects that have been temporarily halted or abandoned give an insight into issues that must be avoided in the future
Since the circulating fluid moves through fractures, it is in direct contact with the rock formation, which leads to salt deposition risk. This experience has taught the geothermal community that flow assurance needs to be addressed ahead of time to prevent issues triggered by the chemical interaction between the injected fluid and the receiving rock, which can impair the overall success of an EGS project
Summary
Enhanced (or engineered) geothermal systems (EGS) have evolved from the hot dry rock concept, implemented for the first time at Fenton Hill in 1977. According to Potter et al (1974), the most suitable rock type for HDR is granite or other crystalline basement rock; temperatures should vary from 150°C to 500°C 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, an average thermal capacity of 250 MWth that could be obtained from the surface heat exchanger, and with pressurized water entering at 280°C and leaving at 65°C Based on these criteria, the potential electrical power that could be generated might amount to 50 MWe at a net efficiency of 20%. 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)
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