Geothermal Power Generated from UK Granites (GWatt)

Lead Research Organisation: University of Exeter
Department Name: Camborne School of Mines

Abstract

Decarbonising power generation is a challenge for the UK, requiring an 80% reduction in greenhouse gas emissions by 2050, relative to 1990 levels. Carbon-free, renewable sources are attractive, but wind and solar generation are intermittent. In contrast, geothermally generated electricity is available all the time (i.e. is 'base load'). In the UK this can be developed with Engineered Geothermal Systems (EGS) whereby very hot water is accessed from depth via deep boreholes (4km or more) and is used to drive a turbine. Pioneering research has shown that permeable rocks (those through which fluid can flow) at depth are often associated with natural fracture systems. However, exploitation of the UK underground thermal resource has been held back by; 1) knowledge gaps about permeability and fluid/heat flow within the fractured hot rocksand 2) a perception that the uncertainty associated with drilling problems or limited fluid flow from deep boreholes are too high for the potential financial reward. This project, Geothermal Power Generated from UK Granites (GWatt), seeks to address these barriers to uptake of EGS 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 & 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.

A particular strength of GWatt is the link with the developing United Downs Deep Geothermal Power (UDDGP) project, an £18M, 2 borehole EGS in the Carnmenellis granite in Cornwall. This will provide a unique resource; downhole fluids, rock samples, geophysical logs, flow data and seismic data. GWatt wil maximise the scientific potential from these data, and carry out innovative further analyses and interpretation, combining site-specific observations with regional studies and state-of-the-art uncertainty quantification, to address the challenges associated with EGS development within SW England. Other UK crystalline basement rocks show fracture-controlled groundwater flow, so the lessons learned from GWatt will ultimately benefit understanding of the rest of the UK deep subsurface.

The project consortium comprises research, business and local government partners. The British Geological Survey, the University of Exeter Camborne School of Mines and Heriot Watt University provide complimentary skills in deep geothermal resource assessments, deep fracture fluid flow, rock/fluid interactions, reservoir modelling, detailed knowledge of the geology of SW England and the quantification of geological uncertainties. Geothermal Engineering Ltd. and Geoscience Ltd. are developing the UDDGP project and provide a wealth of experience delivering UK geothermal projects. 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.

Beneficiaries include local communities through the creation of EGS combined heat and power plants that will be important hubs for renewable energy networks, supplying carbon-free heat and power. The heat can be used for space heating, industrial drying, balneology, greenhouse heating, fish farms etc., all of which will generate local jobs. Local industry will also benefit from the regional scale uptake of EGS within SW England and a potential revival of the minerals industry
arising from technological solutions to extracting metals from the deep geothermal brines.

Planned Impact

In order to meet statuary greenhouse gas emission reduction targets, UK electrical power generation must be decarbonised. Carbon-free renewable generation is currently dominated by wind and solar, but these two technologies produce intermittent supply. Geothermal power generation, via engineered geothermal system (EGS) technology, produces a continuous base-load of carbon-free supply that meets the energy trilemma of security, affordability and sustainability.
The beneficiaries of the proposed EGS research include:

1) Local communities, regional and national governments: A fully developed 2 borehole EGS system loop could generate up to 10 MWe as well as tens of MWth of heat. Through directional drilling technology, several EGS loops could feed a single Combined Heat and Power (CHP) plant. These CHP plants would be important hubs of renewable energy networks, supplying carbon-free heat and power to local communities and playing an important role in meeting regional and national renewable energy targets. The heat can be used for space heating, industrial drying, balneology, greenhouse heating, fish farms etc., all of which will generate local jobs. The Cornwall & Isles of Scilly Local Enterprise Partnership (CIoS LEP) estimate that a 100 MWe of installed geothermal power could provide electricity to c. 150,000 Cornish homes. Based on a study by the Geothermal Energy Association, 100 MWe will involve 1,400-1,700 high quality, long-term FTE jobs. GWatt will help early development of this industry, and thus help job creation, through direct employment and indirectly through 'spin off' industries.

2) The geothermal industry: The basic concepts of EGS (including older descriptors; HDR - Hot Dry Rock, and HWR - Hot Wet Rock) have been proposed for over 40 years. Take-up of the technology by industry requires an increased understanding of heat exchange / transport at depth, both facilitated by GWatt research. Extrapolation of the research findings from site- to regional-scale will enable the creation of more EGS operations. This is especially promising for granites in SW England, as they have a common geological source and bear many similarities to each other. An increased understanding of the regional fracture networks and deep fluid flow within them will enable the location of EGS systems to be more widespread and nearer locations of heat demand, substantially increasing the revenue of a CHP plant.

3) Financiers, investment trusts and venture capitalists: One of the identified barriers to EGS development has been the problem of raising finance to drill deep boreholes; the risk is often perceived as being too high. By quantifying EGS uncertainty using analysis techniques from the hydrocarbons industry, the research findings of GWatt will determine risk in a robust form and one that energy financiers are well versed in. This could potentially unlock the financial reserves to
overcome this significant barrier.

4) The minerals industry: Identifying the scientific and technological solutions to extracting metals from deep brines can create another revenue stream for EGS and so help its economics, and it will reinvigorate the mineral extraction industry in SW England without the need for large mining operations. The hot geothermal brines carry a certain amount of dissolved metals, especially given the highly mineralised nature of the rocks in SW England. Modern electrochemical extraction
technologies can be fitted to surface plant to capture these metals (e.g. strategically important metals to new technologies such as lithium, but also more traditionally important metals such as copper) as the hot brine is recirculated through the EGS flow loop. GWatt will quantify metal concentrations in solution, which when combined with fluid flow data, will provide constraints on amounts of metals than can be recovered.

Publications

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