Development of deep geothermal energy resources in the UK

Deep geothermal exploration in the UK in the 1980s resulted in only one operative borehole (in Southampton). In 2004, a 995 m deep borehole was drilled into the Weardale granite in County Durham. This project differed markedly from the earlier ‘hot dry rock’ investigations in the granites of Cornwall, in that it deliberately targeted possible high natural permeability derived from large fault zones. The new approach met with success, discovering what is believed to be the highest natural permeability ever found in granite anywhere in the world. Drilling of a second borehole at Eastgate in 2010 confirmed that high permeability is preferentially associated with major west–east geological faults. Further deep drilling is now targeting similar faults cutting nearby sedimentary sequences. Meanwhile, renewed interest is being shown in Cornish prospects, as well as in previously unexplored resources in Scotland and Northern Ireland. There is also significant interest in the possible geothermal exploitation of hot brines, which are co-produced with hydrocarbons in existing oilfields. Technological advances in directional drilling, reservoir stimulation and power generation using binary-cycle turbine plants are finally making deep geothermal energy a realistic target for full-scale development in the UK.