An Innovative Computational Approach for Modeling Thermo-hydro Processes within Enhanced Geothermal System

Abstract

An innovative computational approach to capturing the essential aspects of an Enhanced Geothermal System (EGS) is formulated. The modified finite element method is utilized to model transient heat and fluid flow within an EGS reservoir. Three main features are modified to determine their impact on the reservoir: the fracture model, the porous model, and the coupling physical model. For the first feature, the fractures are modeled as a two-dimensional subdomain embedded in a vast three-dimensional rock mass. The fracture model eliminates the need to create slender fractures with a high aspect ratio by allowing reduction of the spatial discretization of the fractures from three- to two-dimensional finite elements. In this model, pseudo three-dimensional equations are adopted to drive the physics of heat and fluid flow in the fractures. In the second feature, a porous subdomain with effective transport properties is modeled to integrate a thermally-shocked region in the reservoir simulation. In the third feature, three-dimensional heat flow in the rock mass is coupled to the two-dimensional heat and fluid flow in the fractures. Numerical examples are computed to illustrate the computational capability of the proposed model to simulate heat and fluid flow in an EGS. Results show that the proposed model is capable of both effectively integrating thermal fractures into reservoir simulation, as well as efficiently tackling the computational burden exerted by high aspect ratio geometries. A parametric analysis is also performed in which the effect of thermal fractures and thermally-shocked region on reservoir performance is evaluated.