Hydrogeothermal studies in the United Kingdom

Following the increase in oil prices in the mid-1970s, Britain assessed its geothermal resources. Low-temperature, hot-water resources, in the range 4 0 degrees C to 100 degrees C, occur in Permo-Triassic sandstones in several deep sedimentary basins. In total these resources are estimated at 69.1 x 10(18) joules (J) (2576 million tonnes coal equivalent). Resources also occ ur in Upper Palaeozoic aquifers but, as the permeability of these aquifers depends upon fissures, exploitation is difficult. The only surface manifest ations of hot water at depth are the warm springs at Bath and Bristol and i n the Peak District and Taff Valley, which issue from the Carboniferous Lim estone; The potential of radiothermal granites for Hot Dry Rock (HDR) devel opment has also been investigated, particularly in the Cammenellis granite in Cornwall. Three boreholes drilled in the granite to depths of over 2 km have been connected by developing natural fractures. Water circulation betw een the boreholes and through the fractured rock has been successful.