Abstract
The postulate that geothermal energy might be recoverable from strata laterally equivalent to the Fell Sandstone Formation (Carboniferous: Mississippian) beneath Newcastle upon Tyne has been examined by the drilling and testing of the 1821 m deep Newcastle Science Central Deep Geothermal Borehole. This proved 376.5 m of Fell Sandstone Formation below 1400 m, much of which resembled braided river deposits found at outcrop, although some lower portions were reddened and yielded grains of aeolian affinity. Downhole logging after attainment of thermal equilibrium proved a temperature of 73°C at 1740 m, and allowed estimation of heat flow at about 88 mW m −2 . This relatively high value probably reflects deep convective transfer of heat over a distance of >8 km from the North Pennine Batholith, along the Ninety Fathom Fault. The Fell Sandstone traversed by the borehole proved to be of low hydraulic conductivity ( c . 7 × 10 −5 m d −1 ). The water that entered the well was highly saline, with a Na–(Ca)–Cl signature similar to other warm waters encountered in the region. It remains for future directional drilling to establish whether sufficient natural fracture permeability can be encountered, or wells stimulated, to support commercial heat production.
Highlights
Exploration for deep geothermal resources in the UK was concerted from the mid-1970s to the early 1980s (Downing & Gray 1986)
Reservoirs with natural temperatures high enough to obviate recourse to heat pumps are more attractive; this is the goal of deep geothermal exploration as currently practised in the UK (Younger et al 2012)
Combination of temperature measurements with thermal conductivity data from a nearby borehole penetrating the same succession has allowed calculation of a heat flow of 88 ± 1 mW m−2. This is significantly above typical background values for the UK (c. 50 mW m−2) and is encouraging from the perspective of geothermal exploration. If such heat flows can be harnessed, the potential benefits are significant: Busby (2010) calculated the inferred geothermal resource for the UK to be around 300 × 1018 Joules for heat that could be abstracted from Permian and younger deeply buried rocks in UK sedimentary basins
Summary
Exploration for deep geothermal resources in the UK was concerted from the mid-1970s to the early 1980s (Downing & Gray 1986).
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