A Comparison of HDR Geothermal Sites

Abstract

A review of HDR projects has been carried out to establish the major controls on the performance of HDR reservoirs. The performance of an HDR system is measured in terms of water loss, pressure drop and thermal behaviour and it is clear that the different experimental HDR reservoirs have exhibited different performances. For example the Fenton Hill HDR reservoir at Los has a minimum water loss when operated at high overpressure whilst the Rosemanowes reservoir has minimum water loss at much lower pressures. These different results may be explained in terms of the fracture geometry, morphology and material properties, the magnitude of the differential stresc and the magnitude of the least principal stress. These properties together describe the ease with which existing fractures may be opened and kept open by hydraulic stimulation and the extent to which they have been sealed over geological time. Issues of fracture network connectivity and rock material properties appear, in the majority of cases examined, to be of secondary importance.