A Review of Simulation Models of Heat Extraction for a Geothermal Reservoir in an Enhanced Geothermal System

Abstract

This paper reviews the heat transfer model for geothermal reservoirs, the fracture network in reservoirs, and the numerical model of hydraulic fracturing. The first section reviews the heat transfer models, which contain the single-porosity model, the dual-porosity model, and the multi-porosity model; meanwhile the mathematical equations of the porosity model are summarized. Then, this paper introduces the fracture network model in reservoirs and the numerical method of computational heat transfer. In the second section, on the basis of the conventional fracture theory, the PKN (Perkins–Kern–Nordgren) model and KGD (Khristianovic–Geertsma–De Klerk) model are reviewed. Meanwhile, the DFN (discrete fracture network) model, P3D (pseudo-3D) model, and PL3D (planar 3D) model are reviewed. The results show that the stimulated reservoir volume method has advantages in describing the fracture network. However, stimulated reservoir volume methods need more computational resources than conventional fracture methods. The third section reviews the numerical models of hydraulic fracturing, which contains the finite element method (FEM), the discrete element method (DEM), and the boundary element method (BEM). The comparison of these methods shows that the FEM can reduce the computational resources when calculating the fluid flow, heat transfer and fracture propagations in a reservoir. Thus, a mature model for geothermal reservoirs can be developed by coupling the processes of heat transfer, fluid flow and fracture propagation.

Heat Extraction in Geothermal Systems with Variable Thermo-Poroelastic Fracture Apertures

“…Fractures indisputably constitute the principal conduits for fluid flow within the confines of heat-containing rock formations characterized by their inherently low permeability, which is a fundamental aspect governing the efficacious exploitation of subsurface resources [14,15]. Therefore, in a bid to markedly enhance the veracity and predictive capability of numerical models, and to judiciously inform the design and execution of future field measurement campaigns, it becomes quintessentially imperative to ascertain the multifaceted impact exerted by the synergistic interplay of fully coupled thermo-poroelastic processes on the morphological attributes of fracture aperture within a discretely fractured reservoir.…”