Numerical simulation study on the heat extraction performance of multi-well injection enhanced geothermal system

This study proposed a multi-well injection enhanced geothermal system (EGS) model for fracture-mode hot dry rock (HDR) heat extraction, which is capable of injecting sufficient mass flow and providing more fluid flow channels for fully heat mining. A thermal-hydraulic model was established and the variation of temperature and pressure distributions, conductive and convective heat fluxes in fracture-mode HDR reservoir were studied. Meanwhile, the sensitivity analysis of operation parameters and fracture parameters was conducted. The results indicated that multi-well injection system can obtain a high heat extraction ratio after 30 years in fracture-mode reservoir. The conduction process is much weaker than the convection process in HDR reservoir, convective heat transfer plays a leading role in the entire heat transfer process. Both the injection temperature and injection mass flow rate are the key parameters affecting the heat extraction performance under the simulation condition. When the injection temperature increased from 283.15 K to 293.15 K, the heat extraction ratio after 30 years decreased from 77.7 % to 71.8 %. When the injection mass flow rate increased from 80 kg/s to 160 kg/s, the heat extraction ratio after 30 years increased from 57.6 % to 84.7 %. The appropriate injection temperature and mass flow rate selection should be based on the specific reservoir conditions and production needs. The production pressure and fracture permeability mainly have effect on the variation of injection pressure, reasonable choice of these parameters is conducive to cost savings. The fracture aperture has little effect on the heat extraction performance. This study provides some reasonable suggestions on better heat extraction performance in multi-well injection EGS and has guidance effect for practical projects.