Comparative investigation on the heat extraction performance of an enhanced geothermal system with N2O, CO2 and H2O as working fluids

Abstract

• A two-dimensional thermo-hydraulic-mechanical coupled model is established. • The heat extraction performances of N 2 O, CO 2 and H 2 O EGS are compared. • The sensitivity analysis of injection-production parameters is carried out. • The heat extraction performances of N 2 O-EGS and CO 2 -EGS are basically the same. • Compared with H 2 O, N 2 O and CO 2 are more suitable as geothermal working fluids. The properties of geothermal working fluids have great influence on the heat extraction performance of an enhanced geothermal system (EGS). In addition to H 2 O, N 2 O and CO 2 have also been proposed as geothermal working fluids. In order to analyze and compare the heat extraction performances of the N 2 O, CO 2 and H 2 O EGS, a two-dimensional thermo-hydraulic-mechanical (THM) coupled EGS model with discrete fractures is established. In addition, the influences of injection-production parameters on the heat extraction effects of EGS with different working fluids are also analyzed. The results indicate that the heat extraction performances of N 2 O-EGS and CO 2 -EGS are almost the same under the same conditions. Taking into account the stable production time and the stability of supporting equipment, the performances of N 2 O-EGS and CO 2 -EGS are better than H 2 O-EGS. Furthermore, a lower injection temperature is conducive to the heat extractions of N 2 O-EGS and CO 2 -EGS, while the injection mass flow rate and production pressure should be designed reasonably according to the actual situation. As for H 2 O-EGS, a higher production pressure is conducive to its performance, while its injection temperature and injection mass flow rate should be designed reasonably.