Prof 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 (Beamish and Busby 2016). 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.
>Could Cornish granite unlock deep geothermal energy in England?
Online article and interview in Power Technology (May 2019)
United Downs Deep Geothermal Power Project (St Day - Carn Marth Granite)
The United Downs Deep Geothermal Power (UDDGP) Project, run by Geothermal Engineering Limited, targetted a granite-hosted segment of the Porthtowan Fault Zone and is developing a 1-3 MW pilot power plant.
Drilling of 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 2214 m (TVD) UD-2 injection well was completed on 28th June 2019. An extended testing programme is currently taking place, before construction of the power plant.
The rationale and science behind the project are explained in this brilliant video. A summary of site selection and an initial assessment of the structurally-controlled reservoir from downhole data has been provided by Reinecker et al. (2021).
Eden Geothermal Project (Bodelva - St Austell Granite)
Eden Geothermal Ltd has been set up by three partners: Eden Project, EGS Energy Ltd, and Bestec (UK) Ltd. The initial drill site is located to the north of the Eden Project biomes, in the southern part of the St Austell Granite, and has targetted the NNW-SSE "Great Cross-course" fault system.
Drilling of the first well, EG-1 (MD 5277 m BGL; TVD 4867 m BGL), commenced on 17th May 2021 and maximum depth was reached on 26th October 2021. It is presently (just!) the longest geothermal well in the UK.
The Project will include a one-year period of heat production from the single deep well, using a ‘co-axial’ circulation system, that will be used to provide direct heat to existing facilities at Eden and to new greenhouses. This will be the first phase of an anticipated two well development. It will pave the way for the second phase and another deep well and an electricity plant.
The project is summarised here.
My research related to deep geothermal energy
The geological uncertainties related to the development of deep geothermal largely relate to 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 geology-related deep geothermal research projects that I’m involved in are summarised below:
PhD title: Geological controls on heat production and the evolution of fracture systems.
PhD student: Philip Henes
The research will use data derived from well-cuttings and downhole geophysical logging to evaluate the geological controls on heat production and fluid flow in the vicinity of the test site. These data will help address how the distribution of heat-generating elements, U, Th, K, varies with depth and so contributes to the heat resource and geothermal gradient. Downhole geophysical logs will be used to determine the orientation, aperture, spacing, distribution and other characteristics of the fracture and vein populations. These are the primary controls on permeability and fluid flow. The vein systems reflect multiple episodes of fracture formation / reactivation and fluid flow - they are, in essence, markers of palaeo-geothermal systems. The nature of vein infills is strongly correlated with wall-rock alteration / strength of the host granite; this, together with re-fracturing and/or dissolution of vein infill exerts an important control on permeability and, potentially, the chemistry of contemporary fluids. The objective is to understand the extent to which multiple generations of fluid flow have contributed to: (1) enhancement, and (2) reduction of permeability.
A second PhD project "Estimation of the geothermal resource" is being undertaken by Ben Adams and is supervised by Professor Hylke Glass (lead) and Dr Robin Shail.
Funding: European Regional Development Fund + College of Engineering Mathematics and Physical Sciences
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)
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 complementary skills in deep geothermal resource assessments, deep fracture fluid flow, rock/fluid interactions, reservoir modelling and the quantification of geological uncertainties.
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)
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 cuttings 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).
Funding: UKRI-NERC + GeoScience Limited