Effects of fracture aperture distribution on the performances of the enhanced geothermal system using supercritical CO2 as working fluid

Abstract

Enhanced Geothermal Systems (EGS) technology has the potential to be a significant source of clean, renewable energy worldwide. A promising alternative to water as the working fluid in EGS is the supercritical carbon dioxide (scCO2), which simultaneously contributes to reducing the atmospheric greenhouse gas emissions. The existing thermal-hydraulic coupled numerical models for non-isothermal two-phase flow in fractured porous media overlook the fracture aperture distributions, which significantly affects EGS performance. This study employs a discrete fracture model with a normal distribution of fracture apertures to investigate the EGS energy performance and carbon sequestration ability. The Monte Carlo method is applied to ensure the simulation results reach a statistical equilibrium from multiple realizations. Results show that the aperture distribution significantly affects EGS performances. The cumulative energy output and total sequestered scCO2 mass can be roughly divided into three stages based on fracture aperture distributions. On the other hand, the effects of aperture distribution become more important as the increase of mean fracture aperture and the reduction of injection pressures. Furthermore, comparing the performances of the EGS using scCO2 and H2O as working fluid, the study found that scCO2-EGS performs better with larger injection pressure, but it is more sensitive to aperture distribution.