A theoretical study of geothermal energy extraction

Efficient extraction of geothermal energy from a dry well depends on the ability to establish a closed pressurized circuit of water through a large zone fractured in hot impermeable rock. Long‐term perpetuation of significant power extraction depends, in addition, on the ability to extend the initial fracture zone through the effects of thermal stress cracking of the adjacent hot rocks. In support of an experimental program to test the feasibility of using this type of energy source, we have solved numerically the combined equations describing the coupled processes of fluid flow, heat transport, and rock fracture. The results show a strong dependence on the extent to which underground pressure can be maintained and the fracture zone continuously extended. They indicate that under favorable, but perhaps not unreasonably exotic, circumstances the extraction of significant thermal power from each well can be expected to continue for many decades.