Estimating the multi-scale distribution of CO2 using seismic data at Sleipner

Seismic data at the Sleipner CO 2 storage project are used to gain insights into the spatial distribution of CO 2 , revealing the fraction of the pore volume occupied by CO 2 at different scales. The CO 2 storage capacity coefficient (C c ) is determined and then scaled by estimates of the fractional area and fractional volume occupied by CO 2 to determine a volume storage coefficient, V c . Estimates of V c are close to the independently determined maximum layer saturations for the case of CO 2 columns under conditions of gravity equilibrium. The analysis is useful for understanding the nature of CO 2 storage efficiency measures and for storage capacity estimates in general. The methods were applied to a dataset derived from time-lapse RMS amplitude difference maps for 9 repeat surveys (1999–2020) and then compared to an FWI velocity model of the 2010 survey, which allowed a layer-by-layer analysis. The macroscopic storage efficiency at Sleipner is found be in the range of 1–6% depending on the reference pore volume used in the analysis, while the fraction of the within-plume pore space occupied by CO 2 within each layer is found to lie in range of 30% and 60%. The methods proposed here have the potential to significantly improve the quantitative analysis of seismic data used for monitoring other CO 2 storage sites.