Massively Parallel Fully Coupled Implicit Modeling of Coupled Thermal-hydrological-mechanical Processes for Enhanced Geothermal System Reservoirs

Development of enhanced geothermal systems (EGS) will require creation of a reservoir of sufficient volume to enable commercial-scale heat transfer from the reservoir rocks to the working fluid. A key assumption associated with reservoir creation/stimulation is that sufficient rock volumes can be hydraulically fractured via both tensile and shear failure, and more importantly by reactivation of naturally existing fractures (by shearing), to create the reservoir. The advancement of EGS greatly depends on our understanding of the dynamics of the intimately coupled rockfracture-fluid-heat system and our ability to reliably predict how reservoirs behave under stimulation and production. In order to advance our understanding of how reservoirs behave under these conditions, we are developing a physicsbased rock deformation and fracture propagation simulator by coupling a discrete element model (DEM) for fracturing with a continuum multiphase flow and heat transport model. In this approach, the continuum flow and heat transport equations are solved on an underlying finite element mesh with evolving porosity and permeability for each element that depends on the local structure of the discrete element network. This paper describes the first phase of development of the simulator, detailing the development of a parallel, fully coupled, implicit, multiscale geothermalgeomechanical simulation code. The initial code development is being conducted considering only single-phase (water saturated) flow coupled with continuum heat transport and rock mechanics models. DEM and fracture propagating capabilities will be added in the next phase of the code development.