A global review of enhanced geothermal system (EGS)

The goal of this study is to review 18 significant enhanced geothermal system (EGS) sites and technologies that have been applied in the European Union, Japan, South Korea, Australia and the USA. The results of earlier cases indicate that the site characteristics, such as a transtensional type setting, are a key factor of successful EGS development. This study also introduces the Enhanced Geothermal Innovative Network for Europe (ENGINE), which focuses on developing high-temperature instruments for the characterization and exploitation of supercritical geothermal reservoirs, as well as the geothermal engineering integrating mitigation of induced seismicity in reservoirs (GEISER). The energy reserves in the upper 10 km of the earth's crust are approximately 1.3 x 10(27) J, which could supply the global energy use for approximately 217 million years. The exploitable geothermal potential can reach 1200 GWe based on an estimated probability of 70%. In 2050, there will be more than 70 GWe of EGS based on an estimated probability of 85%. In view of the immature technologies for EGS, the US has funded a total of 0.22 billion USD from 2007 to 2013 to develop innovative exploration, reservoir stimulation, and sustainable reservoir technologies and economic analysis models for the commercialization of EGS. The crucial issue in Taiwan's geothermal development is the enhancement of the poor productivity of geothermal production wells. Based on foreign experience, increasing the productivity by adding reinjection wells in traditional hydrothermal fields should be a feasible approach for the development of EGS in Taiwan. The study suggests that Taiwan should establish a geothermal exploration database. In addition, the enhancement of geothermal production by developing reservoir simulation and reservoir maintenance technologies will lead to cost reductions. Finally, promoting traditional hydrothermal geothermal power plants to drive EGS development will allow for the stable expansion of Taiwan's geothermal industry.