Influence of Fracture Shearing on Fluid Flow and Thermal Behavior of an EGS Reservoir - Geothermal Code Comparison Study

Abstract

This paper summarizes the results from three problems that were developed for the Geothermal Code Comparison Study organized by the United States Department of Energy Geothermal Technologies Office. The problems in the study were designed to involve different physical processes related to geothermal reservoir engineering and Enhanced Geothermal Systems. The three problems described in this paper, Problems 2, 3, and 6, were focused on processes related to coupling of fluid flow and fracture deformation. Twelve groups participated in the study, each using separate numerical approaches, though not all groups participated in every problem. Problem 2 was a continuum approach to shear stimulation of randomly oriented fractures due to injection of cold water. Problem 3 involved injection into three fractures and investigated the coupling of fluid flow, fracture shear, and fracture opening. Problem 4 involved injection into a fault surrounded by a poro-thermoelastic medium. Comparison of results between groups showed broad agreement, though a some discrepancy was present. Matches between the codes were imperfect because of the different numerical approaches used by the groups and because of the difficulty of communicating between groups to ensure that simulations were performed with identical constitutive relations and input parameters.