GRSG Conference 2020 Presentation
Title: Understanding fault-controlled geothermal reservoirs and their tectonic history based on remote structural mapping
Author: Christopher Yeomans
Remote geological mapping has been a common reconnaissance tool for well over a century; however, with international disruption due to the coronavirus pandemic, remote mapping has now become a necessity and is central to many projects.
Geothermal energy exploration, under the GWatt research consortium, has continued in southwest England throughout the global pandemic. The disruption caused due to national lockdowns and campus closures has caused a refocusing of time and resources that has enabled greater scope for remote mapping of structures across the region.
Current deep geothermal energy targets in the region are fault-controlled reservoirs.
Structural mapping is therefore critical to understanding the resource potential of the region and these remote studies will feed into future reservoir characterisation models.
The structural geology of the southwest region is complicated. Devonian-Carboniferous sedimentary basins, deformed during the Variscan Orogeny, are host to the Cornubian Batholith; a suite of high-heat producing granites.
The batholith is cut be a fault network that largely developed by the end of the Permian, following episodes of post-orogenic extension and intraplate strike-slip tectonics. These structures have been repeatedly reactivated and have controlled palaeo-fluid flow, but their chronology and genesis are poorly understood.
Remote mapping of structures has been carried out across much of the region from both onshore and offshore areas. High-resolution LiDAR data from the Tellus South West project has been merged with bathymetric data from the UK Hydrographic Office.
These datasets provide excellent coverage for remote mapping of structures across southwest England. LiDAR data provide information the onshore expression of faults and largely capture the broader structural features. Bathymetric data enhances this picture by revealing detailed structures observable in submerged outcrops that have been stripped of sediment cover.
Semi-automated analyses have been complemented with manual studies to gain as much information as possible from these data. Different feature extraction methods such as directional and Laplacian filters, the hillshade and tilt derivative transform have been investigated and applied to large areas for rapid mapping of onshore and offshore areas.
The resultant lineament network has been interrogated to identify regional fault trends and potential fault density surrounding major structures. Further manual analyses have subsequently been conducted on specific areas of interest. These aim to identify damage zones and provide the best view of cross-cutting relationships of different fault systems.
We present findings from a range of sites across the southwest region, from the Isles of Scilly in the west to Torbay in the east.
These areas of interest showcase key features of fault zones such as displacements, damage zones and their geometries as we attempt to identify key reservoir characteristics and piece together post-Permian reactivation events that have affected the region.