  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.
