Dr Robin Shail

SW England geothermal

Cornwall and Devon have locally high surface heat flows associated with elevated levels of U, Th and K within the granites of the Cornubian Batholith. It is the most prospective area in the UK for the development of deep geothermal energy. Previous investigations include the £42M CSM Hot Dry Rock research programme (1973-1991), based at Rosemanowes Quarry in the Carnmenellis Granite, where several deep research boreholes were drilled to a maximum depth of 2600 m.

There has been a renewed impetus over the last decade to ensure that the regional potential for deep geothermal power is further investigated and developed; this forms one of the strategic priorities for Cornwall Council. The United Downs Deep Geothermal Power (UDDGP) Project, run by Geothermal Engineering Limited in collaboration with GeoScience Limited, is targetting a granite-hosted segment of the Porthtowan Fault Zone with the intention of developing a 1-3 MW pilot power plant.

Drilling the 5058 m (TVD) UD-1 production well, which is the UK's deepest onshore borehole, commenced on 7th November 2018 and was completed on 23rd April 2019. The UD-2 injection well is 2214 m (TVD) and was completed on 28th June 2019. The HAS Innova drill rig has now been dismantled and is moving to a deep geothermal project in Finland. The next stage of the project is schduled to last until March 2020 and will include a range downhole tests and sidewall coring - details here.

The rationale and science behind the project are explained in this brilliant video

The geological challenges related to the development of deep geothermal include understanding regional to local variations in crustal heat flow and fracture permeability. These are closely aligned with my research interests in SW England granites, SW England mineralisation and post-Variscan tectonics; the geothermal-related research I’m involved in is summarised below.

Article in Power Technology (May 2019): Could Cornish granite unlock deep geothermal energy in England?

Geothermal Power Generated from UK Granites (GWatt)

NERC fourth round highlight topic (2019-2022): Deep subsurface heat as a potential major future energy resource (NE/S003886/1)

Exeter PI: Dr Robin Shail; Exeter Co-I: Dr Matthew Eyre
Research Fellow: Chris Yeomans

Exploitation of UK deep geothermal resources has been held back by knowledge gaps relating to permeability and fluid/heat flow at reservoir target depths of 3-5 km; the risks associated with these uncertainties have inhibited private investment. Geothermal Power Generated from UK Granites (GWatt) seeks to reduce these risks, and so contribute to the uptake of deep geothermal energy, by:

  • Increasing knowledge of the geological conditions needed for deep fracture-controlled fluid flow within granitic rocks.
  • Developing a quantitative understanding of the heat resource and sustainability of the geothermal reservoir.
  • Constructing robust geological risk assessments based on well-established oil and gas uncertainty quantification and optimisation methods, with a view to reducing perceived risks.
  • Applying the integrated results of site-specific research to new geothermal exploration models for other granites, particularly those in SW England.

The project consortium includes research, business and local government partners. Research collaboration between GWatt and the United Downs Deep Geothermal Power (UDDGP) Project will provide access to a unique resource of downhole fluids, rock samples, geophysical logs, flow data and seismic data. In addition to CSM, the project comprises the British Geological Survey (project co-ordinator) and Heriot-Watt University who provide complimentary skills in deep geothermal resource assessments, deep fracture fluid flow, rock/fluid interactions, reservoir modelling and the quantification of geological uncertainties. Geothermal Engineering Limited and GeoScience Limited, as well as running the UDDGP Project, have a wealth of experience in the geothermal sector. Computer Modelling Group Ltd will provide advanced heat and fluid flow modelling software. The Cornwall and Isles of Scilly Local Enterprise Partnership and Cornwall Council will facilitate outreach and dissemination activities, both to local people and the business community.

Geological controls on upper crustal heat flow in Cornwall

NERC Industrial CASE PhD studentship with GeoScience Limited (2018-2022) "Geological controls on upper crustal heat flow for deep geothermal energy in Cornwall" (NE/R008612/1)

PhD student: Chris Dalby
Supervisory team: Dr Robin Shail, Dr Tony Batchelor (GeoScience Limited), Professor Frances Wall, Dr James Hickey

The purpose of the project is to address uncertainties regarding heat production and conduction models in the Cornish crust which include: (i) radioactive elements U, Th and K are not present in sufficiently high quantities within the previously investigated upper parts of the granite to account for observed heat flow, (ii) He-4 production from historical deep geothermal wells is higher than anticipated, (iii) geophysical modelling has progressively reduced the interpreted volume of the Cornubian granites. These inconsistences imply substantive heat source(s) may occur within, or below, the deeper parts of the batholith. Drilling samples from the UDDGP Project will be used to evaluate mineralogical and geochemical changes in depth within the granite to evaluate heat production. These data will be complemented by those obtained during downhole logging. Comparisons between modelled heat production and measured heat flow data will be evaluated in terms of the potential role of upper crustal convective fluid flow and/or mid / lower crustal and mantle heat contributions (using existing deep geophysical data and an understanding of admissible scenarios during the post-Variscan tectonic evolution of SW England).