1980s Geothermal Exploration in the UK can (at last) underpin 2020s sector scale up
Posted on Tuesday, January 14th, 2025
Posted on Tuesday, January 14th, 2025
Four wells drilled to depths deeper than 1 km in the UK from 1979 to 1984 collected important information on the potential for geothermal energy from “hot sedimentary aquifers”. The analyses including production testing, analysing the capability of the aquifer to produce hot water.
Of the four only Southampton went forward into a development. A story on its own, this development into Southampton District Energy scheme was not supported by the Institute of Geological Sciences as they predicted the well would not produce for much more than 5 or 10 years. That it got to development and production for at least 20 years, was more to do with committed collaboration between the public and private sectors, particularly Southampton City Council.
Forty years later it’s very interesting to note that the Southampton well1, although the hottest at 70ºC, should be expected to be poorer in thermal performance than the other loctions. That’s because the aquifer target, the Sherwood Sandstone, which is common to all the wells, was rather thin in Southampton, and the net transmissivity (one key control on productivity) is hence on the low side. In the diagram above, Southampton is predicted with today’s technology to be nevertheless a 4.5 MWth “gusher”. In actual fact, it produced around 2 MW, largely because, we believe, that the rejection temperature was much higher than the 20 ºC assumed in the chart.
The other three sites apparently didn’t make it to development because of a number of factors. For example, IGS were disappointed in the temperature of 50 ºC in Cleethorpes, although they recognized – prophetically in our view – that it was technically feasible to use heat pumps to upcycle the geothermal heat to required target temperatures like 70 ºC for water and space heating.
Larne is perhaps the biggest disappointment of the four. The Sherwood Sandstone came in shallower and therefore cooler than expected and furthermore, despite the thickest development of Sherwood of the four sites, had the poorest quality rock and lowest transmissivity. However, there is good reason to believe, from nearby oil & gas, coal and salt exploration wells, that the Larne location is anomalous, with much better-quality sandstones found in those other boreholes.
Also in Co Antrim, Northern Ireland, Ballymacilroy 1 is a special gift to today’s geothermal developers. That well was originally drilled as coal exploration borehole (yes, really), and when the Sherwood Sandstone came in deeper than expected (so any underlying coals, if present at all, would be too deep), the IGS staff wisely pivoted to collecting hydrogeological data from the well. That including production testing, indicating the second-best transmissivity of the group. The report on the well concluded that the well was capable of 40 L/s of sustained flow.
With today’s drilling and heat pump technologies, experience and knowhow, we now can turn these “warm” sedimentary aquifers into economic projects, cost competitive with fossil fuels. That’s right, clean heat, that is cheaper than fossil fuels without pricing in emissions avoidance.
Although the further we get from these old wells and other deep boreholes, the more we will need to consider pre-drill risk reduction techniques for deeper geothermal prospects, such as geophysical surveys, this historical geothermal and, ironically, fossil fuel resource exploration and development gives today’s geothermal developers a leg up on understanding the potential under our clients’ sites.
Causeway is pushing hard to bring FOAK projects to the UK and Irish markets and we have investment opportunities inside our clean geothermal heat as a service approach. Get in touch to find out more.