Thermoelastic Analysis of Enhanced Geothermal Systems Using a Fully Coupled Thermo-Hydro-Mechanical Model

Abstract

In analysing energy extraction from enhanced geothermal systems (EGS), the thermoelastic effect on characteristic reservoir conditions must be considered. During heat extraction, thermal contraction is induced by cold fluid injection. As a result, thermoelastic deformation is triggered. The induced thermoelasticity could alter the rock's properties, such as 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 multiple fractures. The fracture network system is the primary flow path because the surrounding rock matrix is considered impermeable [6]. The behaviour of the reservoir is studied using different flow boundary conditions. An in-depth analysis is performed to determine the rate at which the thermoelastic effect develops during heat extraction. An application of the analysis is made to investigate a reservoir's characterisation in a different range of scenarios. The results presented have shown the limitations imposed by the thermoelastic effect on the long-term performance of EGS reservoirs.

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