Integrated subsurface characterization of a basin-scale carbon reservoir target

Carbon capture and storage is crucial for reduction of the climate impact of fossil fuel consumption and the only way for the UK to retain energy security without breaching CO2 quotas1. The Utsira sandstone is one of the largest and most widespread sand bodies in the North Sea basin and is identified as a prime target for carbon sequestration due to its large pore volume and ideal subsurface distribution some 800-1200 m beneath the North Sea2. However, its reservoir properties are relatively poorly documented and its top seal capacity to withhold a gas column over human or geological time scales is unknown beyond the immediate vicinity of the successful Sleipner CO2 injection site3. Until 2015, thousands of wells drilled in the North Sea had not encountered any hydrocarbons in the Utsira sandstone raising doubts over its top seal integrity, also questioned by recent (local) studies of seal bypass systems4 and sand injectites5 that affect both the reservoir and its topseal. Existing models for the Utsira sandstone range from deep- to shallow marine and its environment is likely to vary across the basin. The North Sea has been explored for hydrocarbons for over 50 years resulting in a vast legacy database comprising thousands of wells and almost complete 3D seismic coverage allowing unprecedented insights into both reservoir architecture and facies and overburden properties and plumbing systems providing possible pathways for fluid escape into shallower aquifers and eventually to the seabed.

This study will leverage state of the art 3D seismic technology calibrated by wells to provide the first basinwide characterization of the Utsira sandstone and its overburden in order to provide a comprehensive inventory of viable carbon injection sites and top seal risk, which will be key to successful implementation of carbon storage for both UK and Norwegian carbon sources. Generic insights regarding the links between deeper structures, reservoir architecture and overburden leakage paths will be extracted to provide insights into the formation of seal bypass systems in general. Shallow gas reservoirs will be examined to avoid misinterpreting imaging artifacts as leakage paths. The methods and insights developed will have general applicability to basin analysis, petroleum exploration and carbon storage, and will yield crucial insights to inform future policy and implementation of carbon storage strategies. in the UK and Norway.