Numerical Study on Heat Extraction from Supercritical Geothermal Reservoir

Abstract

Recent technology makes it possible to dig a well into the subsurface rocks whose temperatures exceed 400 ?C. These geothermal reservoirs are filled with supercritical water. It is known that water properties significantly change near critical point. Especially heat capacity of water increases dramatically. This means that supercritical water can sweep thermal energy from rock more efficiently than non-supercritical water. In this study, the potential of heat extraction from supercritical geothermal reservoirs, as an extension of Hot Dry Rock / Hot Wet Rock technology, is theoretically evaluated. A numerical analysis code for water flow in fractured rock and heat exchange between rock and water considering changes of water properties is developed. Based on the water circulation model of a single fracture with one injection well and one production well, the changes of water flow patterns with time and efficiency of heat extraction are analyzed. Water flow patterns change during heat extraction due to the changes water properties, and efficiency of heat extraction strongly depends on initial temperature of surrounding rock. Finally, on the point of view of heat extraction efficiency, advantages and disadvantages of using supercritical geothermal reservoirs are summarized.