GWatt – Geothermal PoWer GenerATed from UK GraniTes
The Natural Environment Research Council (NERC)
Sabine den Hartog (PI), Dan Arnold, Andreas Busch, Sebastian Geiger
British Geological Survey (coordinator), University of Exeter Camborne School of Mines, Geothermal Engineering Ltd.,Geoscience Ltd., Computer Modelling Group Ltd., Cornwall and Isles of Scilly Local Enterprise Partnership, Cornwall Council
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. 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 rocks, and 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 will 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.