Seismic monitoring for subsurface uncertainties at the Endurance CO2 store

Abstract

The development of the Endurance structure in the southern North Sea as a CO2 store offers a potentially large decarbonization opportunity for industry along the east coast of England. The Bunter Sandstone Formation in the Endurance structure has been assessed as an excellent candidate for CO2 storage due to its position, depth, reservoir properties, and extensive seal. Monitoring CO2 during active injection and after closure is vital to confirming containment and conformance of the CO2 within the store. There are two key subsurface uncertainties: compartmentalization and vertical permeability. Current seismic resolution does not provide imaging of thin, low-permeability layers that may create low relative vertical permeability, and the high net to gross of the sandstone limits imaging of any minor faulting. However, the strong CO2 response on 4D seismic likely will illuminate baffles and barriers to flow along with variations in reservoir permeability. In 2020, four two-dimensional high-resolution (2DHR) seismic data test lines were acquired to assess the best technology for imaging and monitoring Endurance. High-resolution seismic was concluded to provide quality imaging from the base of the reservoir (approximately 1500 m true vertical depth subsea) up through the overburden to image the entire subsurface and to demonstrate safe storage of CO2.