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

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 Wearda...

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Bibliographic Details
Published in:	Journal of the Geological Society Vol. 164; no. 2; pp. 371 - 382
Main Authors:	Manning, David A. C, Younger, P. L, Smith, F. W, Jones, J. M, Dufton, D. J, Diskin, S
Format:	Journal Article
Language:	English
Published:	London Geological Society of London 01-03-2007 The Geological Society of London Geological Society Geological Society Publishing House
Subjects:	alkalinity Alternative energy sources Aquifers boreholes brines Carboniferous chemical composition Crystalline rocks Durham England Earth sciences Earth, ocean, space Eastgate England Economic geology electrical conductivity Electricity generation Energy policy energy sources England enthalpy Europe Exact sciences and technology Fossil fuels geochemistry Geology geothermal energy geothermal exploration Geothermal power geothermal wells granites Great Britain Green buildings Hydraulic fracturing hydrochemistry Igneous and metamorphic rocks petrology, volcanic processes, magmas igneous rocks isotopes naturally fractured reservoirs Nuclear energy Paleozoic permeability Pilot projects plutonic rocks radioactive isotopes Redevelopment Task forces temperature thermal properties transmissivity United Kingdom vitrinite reflectance Weardale England Weardale Granite Western Europe England Durham England United Kingdom Great Britain Western Europe thermal history till permeability fracture networks enthalpy cuttings boreholes brines Lower Carboniferous Devonian granites sills temperature Cenozoic fractures hot dry rocks vein systems exploration reflectance Quaternary Europe Carboniferous resources igneous rocks intrusions exploration wells transmissivity Paleozoic veins mineralization upper Paleozoic plutonic rocks Phanerozoic
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Summary:	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.
ISSN:	0016-7649 2041-479X
DOI:	10.1144/0016-76492006-015