Numerical simulation of hydro-shearing stimulation in the enhanced geothermal system at the Utah FORGE site

Abstract

Hydro-shearing using low injection rates to stimulate the fractured geothermal reservoir for permeability enhancement. In this work, a series of 3D thermo-hydro-mechanical (THM) coupled simulations were run to investigate the hydro-shearing processes in enhanced geothermal system (EGS). In our model, natural fractures were considered according to the borehole televiewer image results. The enhancement of reservoir permeability was calculated using an empirical model derived from the hydro-mechanical coupling experiments. The THM coupled model was calibrated by reproducing the field monitoring data at the Utah FORGE site. The artificial reservoir volume and its permeability enhancement were investigated during injection test on well 58–32. The modelling results proved that hydro-shearing stimulation does not require the injection pressure to exceed the in-situ minimum principal stress. The hydro-shearing stimulation mechanism is controlled by the water injection induced reservoir cooling and pore pressure increase. For the given injection conditions at well 58–32, the artificial reservoir volume was estimated at about 67,000 m³. The maximum enhancement of reservoir permeability occurs in the vertical direction, thus using horizontal wells is beneficial for geothermal development at this site. The results presented in this work were beneficial for engineers to understand the hydro-shearing stimulation method.