An Investigation of the Thermoelastic Effect in Enhanced Geothermal System Reservoirs Using a Fully-Coupled Thermo-Hydro-Mechanical Model

Abstract

During heat extraction in enhanced geothermal system (EGS) reservoirs, thermal contraction is induced by cold fluid injection. As a result, thermoelastic deformation is triggered. The induced thermoelasticity potentially alters the properties of rock, such as their fracture aperture and permeability, making the thermoelastic effect crucial in understanding EGS reservoir behaviour. Based on coupled thermo-hydro-mechanical (THM) processes extended to include the thermoelastic effect, this paper presents a three-dimensional (3D) numerical model of an EGS reservoir with a multiple planar fracture system to investigate the influence of thermoelasticity on reservoir performance. The behaviour of the reservoir is studied using different operational conditions. An in-depth analysis is performed to determine the rate at which the thermoelastic effect develops during heat extraction by comparing the outcome to a THM model without thermoelasticity. An application of the analysis is made to investigate reservoir parameters in various scenarios employing a parametric study. The results have shown the limitations imposed by the thermoelastic effect on the long-term performance of EGS reservoirs. It is evident from the investigation that in analysing energy extraction from EGS reservoirs, the thermoelastic effect on characteristic reservoir conditions must be considered to accurately capture the behaviour of the system.