Deliverable 2.3b: Stress-induced seismic anisotropy: a promising tool to assess reservoir proprieties and caprock integrity

Abstract

This deliverable assesses the potential of seismic anisotropy to measure stress within the CO2 storage complex, primarily the reservoir and overburden. Using onshore passive seismic and stress data for the UK, we test the potential for shear-wave splitting to be used to monitor the stress field in and above CO2 storage sites. We focus on four regions: Northeast England, Northwest England, Southeast England and South Wales. Stress-induced anisotropy is observed in all regions and is particularly clear in Northwest England and Southeast England. We also show, for the first time, that shear-wave splitting can be measured using seismicity recorded by offshore Permanent Reservoir Monitoring Systems (PRMs). Shear-wave splitting is measured at select PRM stations at the Snorre field using data recorded from the 21st March 2022 MW 5.1 Tampen Spur earthquakes and subsequent microseismic aftershocks (0.1 < $ML < 2.6). These results show that offshore sensors, such as PRM systems, are suitable for measuring shear-wave splitting for microseismic data even in relatively sparse deployments if the sensors are deployed above CO2 storage projects. This makes shear-wave splitting an important potential added value that should be considered when planning offshore passive seismic monitoring of CO2 storage projects.