Impact of Fluid Thermophysical Properties on Long-Term Fluid Circulation and Heat Production in Enhanced Geothermal Systems

Abstract

Enhanced Geothermal Systems (EGS) are a promising technology for harnessing Earth's heat for energy production. Most previous studies simulating EGS processes have assumed constant thermophysical properties, such as density and viscosity, for the circulating fluid. In this study, we modeled several cases with varying fracture geometries to assess the impact of temperature-dependent thermophysical properties, particularly density and viscosity. The results indicate that although density variations with temperature are relatively small, they can still influence simulation outcomes due to their effect on gravity-driven fluid movement. This impact is more pronounced when wells are aligned vertically, leading to predominantly vertical fluid flow. In contrast, viscosity exhibits a significant reduction with increasing temperature. At the high temperatures typical of the Utah FORGE site, viscosity can decrease by an order of magnitude. Incorporating temperature-dependent viscosity in the simulations significantly lowered production temperatures and slowed fracture propagation. Based on these findings, it is crucial to account for temperature-dependent density and viscosity variations when conducting EGS reservoir simulations to ensure more accurate predictions.