Geothermal energy offers a sustainable source of heat and electricity but alters reservoir pressure and temperature, affecting in-situ stress and potentially triggering fault reactivation and induced seismicity. Deep geothermal reservoirs are valuable for their high temperatures but pose challenges like low permeability and fracture-dominated flow, increasing the risk of fault instability.

This study explores two approaches to assess stress changes: a semi-analytical geomechanical proxy and a fully-coupled Thermo-Hydro-Mechanical (THM) model using open-DARTS. The THM model simulates coupled thermal, hydraulic, and mechanical processes in complex rock formations, while the proxy method approximates displacements and stress changes using reservoir simulation outputs and homogeneous geomechanical rock properties assumptions.

The proxy model has been applied to matrix- and fault-dominated systems, including the Brugge dataset. Results include pressure, temperature, displacements, stress changes predictions over 30 years. Fault stability is evaluated using Mohr-Coulomb criteria with a constant friction coefficient.

In fracture-dominated systems, faults often control flow but. Discrete Fracture Model (DFM) has been used for flow modelling.

Combining proxy and THM models can optimize the balance between accuracy and computational cost. The study emphasizes the differing impacts of pressure and temperature on fault stability during geothermal operations.

Underground energy storage (UES) in porous and cavity reservoirs can be used to balance the mismatch between the production and demand of renewable energy. Understanding the geomechanical behaviour of these reservoirs under different storage conditions, i.e., storage frequency and fluid pressure, is key in defining their capacity and effective lifetime. This work presents an analysis performed on sandstones to unravel their geomechanical response under cyclic loading. It includes, importantly, both experimental and numerical investigations under deviatoric stress conditions below the rock dilatant cracking threshold. From the experimental point of view, axial strains and acoustic emissions indicated that inelastic strains accumulated cycle after cycle, following a decreasing rate per cycle. Four types of deformations were interpreted: elastic, viscoelastic, plastic, and cyclic-plastic. Based on these experimental results and observations, the Modified Cam-clay model was extended to account for cyclic plastic deformations and the Kelvin-Voigt model was used to model visco-elasticity. This approach can be used to study cyclic sandstone deformation’s implications on subsidence, fault reactivation, and cap rock flexure, among other physical phenomena impacting a reservoir’s storage capacity.