A fully coupled numerical model of thermo-hydro-mechanical processes and fracture contact mechanics in porous media

TL;DR

This paper introduces a comprehensive numerical model that simulates the complex interactions of thermal, hydraulic, and mechanical processes in fractured porous media, enhancing understanding of subsurface phenomena.

Contribution

It presents a novel mixed-dimensional thermo-hydro-mechanical model with explicit fracture contact mechanics, implemented in an open-source framework, for improved subsurface process simulation.

Findings

Model demonstrates convergence in simulations

Reveals effects of process-structure coupling

Applied to geothermal pressure stimulation scenario

Abstract

A range of phenomena in the subsurface is characterised by the interplay between coupled thermal, hydraulic and mechanical processes and deforming structures such as fractures. Modelling subsurface dynamics can provide valuable phenomenological understanding, but requires models which faithfully represent the dynamics involved; these models, therefore are themselves highly complex. This paper presents a mixed-dimensional thermo-hydro-mechanical model designed to capture the process-structure interplay using a discrete-fracture-matrix framework. It incorporates tightly coupled thermo-hydro-mechanical processes based on laws for momentum, mass and entropy in subdomains representing the matrix and the lower-dimensional fractures and fracture intersections. The deformation of explicitly represented fractures is modelled by contact mechanics relations and a Coulomb friction law, with particular attention on coupling of fracture dilation to the governing equations in both fractures and matrix. The model is discretised using multi-point finite volumes for the balance equations and a semismooth Newton scheme for the contact conditions and is implemented in the open source fracture simulation toolbox PorePy. Finally, simulation studies demonstrate the model's convergence, investigate process-structure coupling effects, explore different fracture dilation models and show an application of the model to a 3d geothermal pressure stimulation and long-term cooling scenario.