Investigation on the characteristics of hydraulic fracturing in fractured-subsequently-filled hot dry rock geothermal formation

Geothermal energy plays a significant role in meeting the energy demand and achieving the decarbonization transition. To break through the technology bottleneck of traditional EGS and guide large-scale and efficient exploitation of hot dry rock (HDR) geothermal, this paper performed hydraulic fracturing simulation experiments with real fractured-subsequently-filled HDR formation rocks focusing on the effects of confining stress and temperature on breakdown pressure, fracture pattern and fracture permeability. Results indicated that a higher temperature and a lower confining pressure resulted in a smaller breakdown pressure and a larger fracture permeability. Additionally, the hydraulic fractures always propagate along the backfill, which is independent of temperature and stress conditions. Finally, based on the structural characteristics of natural deep HDR mass and the research results, the Filled Fracture - based Enhanced Geothermal System (FF-EGS) was proposed for fractured-subsequently-filled HDR geothermal mining. FF-EGS is a disruptive breakthrough in the field of HDR geothermal development technology. The results are expected to provide theoretical guidance and technical support for large-scale, efficient and low-cost construction of high-permeability HDR reservoirs, and also provides the possibility for large-scale commercial utilization of HDR geothermal resources.