Heat Extraction from HDR Geothermal Reservoirs

Abstract

Commercial development of HDR geothermal resources requires estimates of extractable heat content and potential for optimum heat extraction rate and production lifetime under givcn reservoir structure and fluid circulation conditions. Major parameters in evaluation of resources are the volume (heat content) of the heat extractable reservoir, the fracture distribution that governs the hydraulic regime (mean residence time), and the mean fracture spacing of rock-block size distribution that governs the rate of heat transfer (thermal conduction time). The relationship of the fluid residence time and the rock block thermal conduction time determines the temperature decline curve under steady production. The total heat extracted is the product of the production flowrate and the increased enthalpy of the circulated fluid. These data can examined from long-term flow tests of the few active and planned HDR reservoirs in the world.