Evaluation of Heat Production from Single Fracture Hot Dry Rock with Applications for EGS Reservoir Design

Abstract

Enhanced Geothermal Systems (EGS) are the most effective methods for extracting geothermal energy from deep hot dry rock (HDR). The EGS reservoir framework is envisioned as independent-multiple fractures connecting injection and production wells. The reservoir is further conceptually represented by a single fracture with homogeneous features, and a unit fracture is defined as having extendibility to a larger surface area for heat extraction. An analytical solution for the thermal-hydraulic coupling process is derived with a 1-D steady state conductive heat flow in the HDR with perpendicular water flow in the single fracture and transient heat transfer from rock to water. The heat produced from the HDR via water flow in the idealized single fracture is demonstrated by arithmetic equations. The lifetime of an EGS reservoir in these reference conditions is 23.2 years and is confined by the produced water temperature of 150°C for commercial utilization. The heat recovery factor is 12.4%. With a power plant capacity of 5 Mw installed, the total area for extracting recoverable heat within the projected lifetime of a fracture surface of 1.58×106m2was determined. The discussion shows the ability of the model to estimate heat production and reservoir scale.