Multi-scale fault and fracture networks of Mississippian carbonate platforms (MCP): implications for extracting geothermal energy

Unlocking the geothermal potential of Britain’s Mississippian carbonate platforms (MCP) could significantly advance the UK transition to net-zero carbon emissions. Geothermal energy offers a reliable and clean heat source, yet comprehensive assessments of geothermal resources remain limited, despite the urgency of decarbonization efforts. The MCP, equivalent to Early Carboniferous limestones (ECL), are linked to thermal springs in Bath, Bristol, the Taff Valley (South Wales), and the Peak District (UK). Their bulk permeability, however, is highly variable, with fluid flow largely governed by faults and fractures. While Belgium and the Netherlands have successfully harnessed similar formations for geothermal energy, the MCP in Britain remain underexplored. Limited seismic data and sparse boreholes reaching the top of the MCP highlight the critical need for further investigations.

Our main focus in this presentation addresses the connectivity of the fault and fractures  in the MCP,through multi-scale data, to provide valuable insights into geothermal energy potential. This study integrates regional, local, and outcrop-scale data from the MCP. Fault and fracture maps are developed using: (a) seismic reflection data and published geological maps, and (b) fieldwork imagery. In situ stress and pore pressure data are drawn from legacy onshore hydrocarbon wells, wireline logs, British Geological Survey reports, and recent publications. Fault stability analyses, incorporating Normalised slip (Ts) and dilation (Td) tendencies, provide insights into likely fault and fracture behaviour. By addressing uncertainties in input parameters, the study evaluates their implications for geothermal resource exploration.

Key findings in this study include: (a) a detailed characterization of fracture network connectivity and patterns in the MCP, (b) refined understanding of regional-to-local fault-fracture interpretations, and (c) permeability estimates under prevailing stress conditions. The integration of outcrop and subsurface data enhances the reliability of the interpretations, bridging the gap between field observations and geological modelling. Additionally, insights into the role of subsurface stress regimes and their impact on fault stability will provide valuable guidance for optimizing drilling strategies and mitigating operational risks.