Repurposing Legacy Boreholes for Microseismic Monitoring: Geothermal Case Study from Cornwall, UK

The geothermal resources of Cornwall, UK, have the potential of providing both power and heat through exploiting natural fracture zones. Understanding and monitoring induced seismicity resulting from stress state changes is important in successfully realizing deep geothermal energy. We explore the potential of repurposing legacy boreholes to provide cost-effective seismic monitoring using instruments deployed in a former geothermal well at Rosemanowes Quarry, Penryn, Cornwall. These 1km deep borehole geophones captured a range of induced and natural seismicity, which include relatively nearby events originating from the United Downs Deep Geothermal Power (UDDGP) project and near Constantine, Cornwall. The lower noise and attenuation levels experienced by the borehole geophone array has significantly increase the detectability rates for both the induced UDDGP and the natural Constantine sequences. After implementing a template-matching method for each seismic sequence, we were able to identify more than three times the number of seismic events when compared with those reported in the BGS catalogue based on surface measurements alone. This larger dataset provides greater insight into induced and natural seismicity of the area, which is of significant value to future deep geothermal projects.