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

Abstract

Seismic data at the Sleipner CO2 storage project are used to gain insights into the spatial distribution of CO2, revealing the fraction of the pore volume occupied by CO2 at different scales. The CO2 storage capacity coefficient (Cc) is determined and then scaled by estimates of the fractional area and fractional volume occupied by CO2 to determine a volume storage coefficient, Vc. Estimates of Vc are close to the independently determined maximum layer saturations for the case of CO2 columns under conditions of gravity equilibrium. The analysis is useful for understanding the nature of CO2 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 CO2 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 CO2 storage sites.