A New T-H-M-C Model Development for Discrete-Fracture EGS Studies

Abstract

A new numerical model is developed for simulating flows and transport in EGS reservoirs with discrete fractures in a geologic medium. A Computational Fluid Dynamics (CFD) element is used in MULTIFLUX for flexibility in simulating any planar, penny- or lens-shaped fractures with laminar or turbulent flow and transport analysis. The fracture aperture of each planar configuration is adjusted iteratively, allowing for: (a) elastic deformation in the fracture system by hydrodynamic pressure; (b) thermal dilatation of the strata; and (c) geochemical precipitation and dissolution. The discrete fractures may form a set of planar fractures, connected with a network of conduits. The CFD model-element is coupled to the sub-model of the host geothermal formation, a porous, fractured, and jointed rockmass. Multi-phase, multi-component heat and fluid flow simulators are used for the geologic submodel, such as TOUGH2 and/or TOUGHREACT. Coupling of the overlaid fracture network system in the CFD model-element to the host geothermal formation applies the NTCF (Numerical Transport Code Functionalization) technique, a modeling accelerator of the iterations in MULTIFLUX. Model validation exercises are shown against Fenton Hill EGS data. A model application example is given for a test EGS site at Desert Peak, NV (ORMAT Technologies)