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Research Progress and Technical Challenges of Geothermal Energy Development From Hot Dry Rock
The reserves of hot dry rock (HDR) geothermal resources are huge. According to statistics, the amount of HDR resources available for human development and utilization is 30 times as all the oil, natural gas and coal resources on the earth. The main method to develop HDR geothermal resources is so called enhanced geothermal system (EGS) using hydraulic fracturing. An artificial geothermal reservoir with high permeability and large heat exchange area is created in the deep high temperature rock mass (e.g., HDR with low porosity and low permeability). Thus, a considerable amount of heat energy can be economically recovered for utilization in the middle- to long-term. After nearly 50 years of research and development, more and more countries have joined the ranks of exploration and development of HDR in the world, as the prospect of commercial exploitation of HDR resources is further clarified. At present, there are more than thirty EGS projects under construction or in operation worldwide. Sixteen EGS projects are generating electricity, and five of them are in operation now. In addition, more EGS projects are still in preliminary demonstration. This paper summarizes the base technologies, key technologies, and game-changing technologies to promote the commercialization of HDR geothermal resources. The development of these technologies is very conducive to making new breakthroughs in HDR geothermal development in China, forming a batch of HDR exploitation demonstration areas, and supporting the adjustment of national energy structure and the realization of the "dual-carbon target". According to the present situation of exploration, development and utilization of HDR at home and abroad, combined with the practice of scientific and technological exploration of HDR in Gonghe basin, the evaluation and site selection, efficient and low-cost drilling and geothermal utilization of HDR geothermal resources are defined as the base technologies. The key technologies include high-resolution exploration and characterization of HDR, efficient and complex fracture network reservoir creation, effective micro-seismic control, fracture network connectivity and reservoir characterization. The game-changing technologies include downhole liquid explosion fracture creation, downhole in-situ efficient heat transfer and power generation, CO2 and other working fluid for high-efficient power generation.