Potential of Enhanced Geothermal System: A simulation study

EGS systems extract heat by circulating a fluid (such as water) through hot rock deep in the ground and can use that heat to produce electrical power. Here we investigate a system where one injection well and two production wells have horizontal sections connected by several transverse hydraulic fractures, thus providing large heat transfer are for the working fluid to pick up heat from the hot rock and transfer it to the surface. The aim of the study is to provide a tool for rapid order-of-magnitude assessment of the effects of essential design variables on the circulating water temperature at the production well outlet as well as on power generation. Our analytical model is based on a simplified version of a model that appeared in literature (Gringarten et al., 1975). Modeling simplifications respect mass and energy conservation laws, but allow for an analytical solution of the simplified partial differential equations, thus enabling rapid parametric investigations. Based on the simplified model, we built an interactive simulation in Mathematica, which produces the rate of heat extraction as well as the water temperature at the outlet as a function of fracture dimensions, fracture spacing, and water flow rate. Simulations indicated that the outlet temperature will drop for an increase in well spacing or water flow rate per well, and a decrease in fracture radius. Similarly, an increase in fracture are enables heat transfer increase towards the thermodynamic upper bound.