A Fully-Coupled Flow-Geomechanics Model for Fluid and Heat Flow in Geothermal Reservoirs

Abstract

Thermally induced rock deformation process in an enhanced geothermal system is vital as coldwater injection induces temperature change, and it causes, as the consequence, stress alterations and contraction of the rock frame. The deformation, in turn, leads to changes in hydraulic properties, such as porosity and permeability. To capture such physical processes, coupled effects need to be considered for the analysis of fluid flow, heat transfer, and mechanical responses. This paper presents a numerical model for a fully coupled, fully implicit flow-geomechanics model for fluid and heat flow in porous media. The simulator is built on TOUGH2 (Pruess et al, 1999), a well-established simulator for geo-hydrological analysis with multiphase, multi-component fluid and heat flow (Rutqvist et al., 2002). Three additional primary variables, namely the displacement of an element interface in x, y, and z direction, are introduced to incorporate the stress equilibrium equations. The numerical scheme is verified against the analytical solutions of 1) one-dimensional consolidation and 2) one-dimensional heat conduction in deformable media (Jaeger et al., 2007). These two problems provide a critical test of our algorithm. In addition, we present an application example for demonstrating the use of the proposed model.