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Journal of the Geological Society; 2007; v. 164; issue.2; p. 371-382;
DOI: 10.1144/0016-76492006-015
© 2007 Geological Society of London

Original Article

A deep geothermal exploration well at Eastgate, Weardale, UK: a novel exploration concept for low-enthalpy resources

D.A.C. Manning1,2, P.L. Younger2, F.W. Smith3, J.M. Jones4, D.J. Dufton5 & S. Diskin6

1 1School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK (e-mail: david.manning@ncl.ac.uk)
2 2Institute for Research on the Environment and Sustainability, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
3 3FWS Consultants Ltd, Merrington House, PO Box 11, Merrington Lane Trading Estate, Spennymoor DL16 7UU, UK
4 4March House, Horsley NE15 0HZ, UK
5 5PB Power, William Armstrong Drive, Newcastle upon Tyne NE4 7YQ, UK
6 6Foraco–Boniface SA, ZI des Fournels, BP 173, 34401 Lunel, France

The first deep geothermal exploration borehole (995 m) to be drilled in the UK for over 20 years was completed at Eastgate (Weardale, Co. Durham) in December 2004. It penetrated 4 m of sandy till (Quaternary), 267.5 m of Lower Carboniferous strata (including the Whin Sill), and 723.5 m of the Weardale Granite (Devonian), with vein mineralization occurring to 913 m. Unlike previous geothermal investigations of UK radiothermal granites that focused on the hot dry rock concept, the Eastgate Borehole was designed to intercept deep fracture-hosted brines associated with the major, geologically ancient, hydrothermal vein systems. Abundant brine (≤46 °C) was encountered within natural fracture networks of very high permeability (transmissivity c. 2000 darcy m) within granite. Evidence for the thermal history of the Carboniferous rocks from phytoclast reflectance measurements shows very high values (≥3.3%) indicating maximum temperatures of 130 °C prior to intrusion of the Whin Sill. Geochemical analysis of cuttings samples from the Eastgate Borehole suggests radiothermal heat production rates for unaltered Weardale Granite averaging 4.1 µW m–3, with a mean geothermal gradient of 38 °C km–1. The Eastgate Borehole has significant exploitation potential for direct heat uses; it demonstrates the potential for seeking hydrothermal vein systems within radiothermal granites as targets for geothermal resources.




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[Abstract] [PDF]