Use of GReS to model geomechanical processes related to fluid production and storage

Underground fluid extraction and injection induce pore-pressure variations that affect the stress state of porous media and may result in ground deformation. The numerical simulation of these processes therefore requires a coupled description of fluid flow and solid deformation. This thesis investigates the poromechanical response associated with a simplified underground fluid production and storage scenario using GReS, a novel numerical framework for coupled geomechanical and flow simulations developed at Dept. ICEA. The theoretical background of poroelasticity and the numerical strategies adopted in GReS are first introduced. The modelling workflow is then examined through the Terzaghi consolidation benchmark and the Deep Aquifer reference example before being applied to a three-dimensional case study. The case study consists of a multilayer geological domain containing a permeable reservoir and aquifer overlain and underlain by low-permeability formations. Fluid production and injection are represented through a prescribed well source term, with an operating history including an initial extraction phase followed by pressure recovery and cyclic extraction and injection. The coupled problem is solved using a fully coupled formulation, and the resulting pressure and displacement fields are analysed in space and time. The results show a clear relationship between the imposed flow-rate variations, the evolution of pore pressure and the resulting deformation. Extraction produces pressure depletion and compaction, while the subsequent injection and extraction cycles generate corresponding pressure and displacement variations. The model also reproduces the propagation of the mechanical response from the reservoir towards the ground surface. Overall, the study demonstrates the applicability of the adopted workflow to the analysis of coupled hydraulic–mechanical processes associated with underground fluid operations. The linear-elastic constitutive model represents the main simplification of the present analysis and provides a basis for future developments using more advanced material behaviour and site-specific conditions.