Top-down and bottom-up estimates of CO₂ storage capacity in the United Kingdom sector of the southern North Sea basin

Calculations of the CO₂ storage capacity in the Leman Sandstone Formation and the Bunter Sandstone Formation in the data-rich southern North Sea basin, using structure contour, porosity, and isopach maps and a simulation of CO₂ injection, suggest that their CO₂ storage capacities are approximately 3 and up to 15 Gt CO₂, respectively. It is recognized that such data are not available for most sedimentary basins, and a simple top-down method of calculating CO₂ storage capacity would be highly desirable from a policy maker's perspective, so that the storage capacity of a basin, region, or jurisdiction could readily be estimated. Therefore, the above estimates were used to calculate the amount of CO₂ stored per unit area and the amount of CO₂ stored per unit of pore volume in the Leman Sandstone and Bunter Sandstone formations. The results were compared to similar calculations, derived from published data, for the Utsira Sand, a CO₂ storage reservoir in the northern North Sea. The mean CO₂ stored per unit area of the formation is 140 kg m⁻², and the range is 42–260 kg m⁻². The mean CO₂ stored per unit pore volume is 6.3 kg m⁻³, and the range is 1.8–10.0 kg m⁻³. Two important factors that vary widely between these three North Sea reservoir formations are the total pore volume in traps and the achievable CO₂ saturation; neither can be determined without detailed data.