Unlocking the UK Geothermal Resource Base

Abstract

The UK’s geothermal resources were evaluated during the 1980’s yet focused solely on Mesozoic sedimentary basins and radio thermal granites. Subsequent investigations have focused on the electricity generation potential of UK geothermal resources even though their relatively low temperatures means they are best suited to supply heat. This aligns well with the UK’s need to decarbonise heat and improve energy security by reducing reliance upon gas imports. Since these earlier evaluations, the UK geothermal resource base has been extended by looking beyond the granites and sedimentary basins to include lower temperature and more novel sources of geothermal fluid such as water contained within flooded abandoned mines, produced water from oil fields and water flowing though deeply buried karst. These enigmatic resources could help to de-risk geothermal energy developments thereby unlocking increased geothermal potential across many regions of the globe. The Earth’s geothermal gradient means that forecasting how temperatures will increase with depth is relatively straightforward. Predicting the permeability at depth is more complex, yet sufficient permeability is key to successful geothermal energy developments. In this paper we evaluate recently identified geothermal resources, present a rationale for their use and assess their contribution to the UK resource base. Although with very different provenances, these systems are all known to flow water. They include tepid water within flooded abandoned mines which underlie the many towns and cities that grew from the strength of their coal reserves, co-produced waters increasingly produced from ageing hydrocarbon wells both offshore and onshore and karst systems that are buried deep enough to provide a geothermal target. The examples we present allow us to increase the both spatial distribution of geothermal resources and the heat in place over and above that which has been previously identified.