Lands End Peninsula of Cornwall, UK. The high-heat-producing granite of Cornwall makes the region a key target for geothermal exploration. Image: Keven Law from Los Angeles, USA, CC BY-SA 2.0, via Wikimedia Commons
Geothermal energy is a key component of the energy transition in Europe, particularly given that many of the required exploration and drilling skills are readily transferable from the oil and gas sector. As the industry expands, the number of papers capturing research from the initial development of a geothermal reservoir through to the economic provision of geothermal energy is rapidly growing.
The UK’s best-known geothermal prospect is the United Downs Deep Geothermal Power project near Redruth, Cornwall. This pioneering, deep geothermal project aims to exploit the high-enthalpy (temperature) Cornubian granite batholith. But the UK has other lower-enthalpy prospects, too, in the form of deep hot sedimentary aquifers (HSAs). England and Wales have four major Mesozoic sedimentary basins with the potential for geothermal exploitation – the Worcester, East England, Wessex and Cheshire basins – yet, despite growing energy demands, currently only the Wessex Basin has been developed, with a single-well scheme that supplies district heating to Southampton. To test whether a similar single-well scheme might be viable elsewhere, Christopher Brown at the University of Glasgow and colleagues provide sensitivity analysis modelling from a single extraction well in the Cheshire Basin, where the Permian Collyhurst Sandstone Formation is expected to be encountered at a depth of between 2.8 and 3.5 km. They use numerical modelling that couples heat and fluid flux to show that such low-enthalpy, deep geothermal systems are affected by geological and engineering parameters including thermal gradient, hydraulic conductivity and production rate, as well as the length and position of the well screen. All of these parameters could affect the success and viability of any single well scheme and must be factored into planning and operational risk.
Ireland is also largely characterised by relatively low-enthalpy geothermal resources, and Joseph English at University College, Dublin, and colleagues review the country’s geothermal prospects using data from the Geological Survey of Ireland. They suggest that shallow resources, exploited via ground sourced heat pumps, offer significant potential. Aside from the Mesozoic basins of Northern Ireland, where porous and permeable Permo-Triassic sandstones are preserved beneath Paleogene basalts, the terrestrial geology offers limited possibilities for deep hydrothermal aquifers with primary porosity and permeability. The team suggest that geothermal exploration could focus on fractured Carboniferous carbonate reservoirs, where groundwater temperatures can reach 38°C at 1 km depth, or on lower-permeability petrothermal reservoirs. Offshore from Dublin, the Triassic sandstone within the Kish Bank Basin has reservoir temperatures of ~ 20-120°C, so could potentially support a local district heating network planned for Dublin city centre.
A fascinating overview of geothermal prospects in Europe (and beyond) is provided in a recent themed issue of the European Geologist, Geothermal energy – A geological contribution to the energy transition. The 12 articles in the edition cover topics including the exploration and exploitation of deep geothermal resources and optimisation of geothermal in heating (and cooling) systems. Several articles discuss how community-based financing can reduce or spread the costs associated with geothermal energy schemes, as well as public perceptions of such energy source applications, with specific focus on CROWDTHERMAL (www.crowdthermalproject.eu) – a Horizon 2020 project that aims to empower the European public to participate in geothermal development via crowdfunding and social engagement.
The flurry of recent geothermal research demonstrates the exciting, diverse and challenging nature of this field, as well as its significance in the greener energy mix, and highlights the importance of knowledge sharing and international collaboration.
Dr Colin Serridge
Details
Q. J. Eng. Geol. Hydrogeol. 55, 2022; doi.org/10.1144/qjegh2021-131
First Break 41, 2023; doi.org/10.3997/1365-2397.fb2023009
