Microseismic monitoring and insights of rupture mechanism from China's pilot EGS project in Gonghe, Northwestern China

Enhanced Geothermal Systems (EGS) are effective means of developing hot dry rock (HDR) type geothermal resources, transforming low porosity and permeability rock masses deep underground into artificial geothermal reservoirs with high permeability through reservoir stimulation. EGS systems can economically extract a considerable amount of thermal energy over the medium to long term to be utilized for power generation. The development and research of EGS has been ongoing internationally for over 40 years. However, at present, the development of EGS is still in the stage of on-site experimental research and development, and its commercial development still faces many challenges. China, like many other countries, is in need of developing deep geothermal resources to meet its energy demands. In 2017, a well named GR1 with a temperature of 236°C was drilled to a depth of 3705m in the Gonghe Basin of Qinghai Province. Recognizing the potential of HDR resources, the China Geological Survey launched an exploration and production project in Gonghe Basin in 2019. Following several critical technological breakthroughs, the first power generation test of HDR was successfully conducted in the Gonghe Basin in 2022. This study offers a detailed introduction to the localization of microseismic events that occurred during thermal reservoir stimulation at different stages of development. By analyzing these microseismic events, we can evaluate the effectiveness and volume scale of artificial thermal reservoir transformation. In addition, we assess the development of natural fractures utilizing data from 3D seismic attributes of the granite, imaging logging, etc. We conclude by discussing implications for successful geothermal development of the specific geological conditions present at the Gonghe HDR field, based on the localization results of microseismic data and the distribution of natural fractures in the field.