Evaluation of heat extraction performance of multi-well injection enhanced geothermal system

Abstract

• Model of multiple-injection and one-production is established using local thermal non-equilibrium. • Effects of reservoir and injection-production parameters on EGS performance were investigated. • Increasing of injection temperature can increases production temperature and prolongs EGS life. • Thermal extraction rate increases with the injection-production distance increases. • Heat recovery rates of four different injection-production well patterns are compared. The well layout can provide fluid channels, which is important for enhanced geothermal system (EGS), then the thermal energy in the rock mass can be used for heat extraction and power generation. The heat extraction rate analysis of injection-production well patterns can provide reference for the heat extraction condition of EGS. Based on the local thermal non-equilibrium theory and random fracture model, the EGS model of four injection and one production was established in this paper. Effects of reservoir parameters and injection-production parameters on production temperature and thermal extraction rate were studied. The results show that the injection temperature and injection-production distance are important parameters that affecting the thermal performance of the EGS. Increasing injection temperature can increases the production temperature and prolongs the EGS life. When the injection temperature increases from 293.15 K to 323.15 K, the production temperature increases from 340.04 K to 354.21 K. The higher the injection-production distance is, the higher the thermal extraction rate is. When the injection-production distance increases from 210 m to 325 m, the thermal extraction rate increases from 41.9% to 56.4%. In addition, heat extraction rates of four injection-production well patterns were compared and analyzed. The heat extraction performance of three-injections and one-production is obviously better than other methods. For the heating demand, the heat extraction rate of this well pattern is 60.34% and its service life is 39.7a. For power generation demand, its heat extraction rate of the well pattern is 55.9%, and its life is 32.7a.