Implementing 4D seismic inversion based on Linear Programming techniques for CO2 monitoring at the Sleipner field CCS site in the North Sea, Norway

Abstract

The critical task of overseeing and validating the storage and confinement of carbon dioxide (CO2) in geological formations or designated repositories, particularly within the framework of carbon capture and storage (CCS) initiatives, involves the meticulous process of CO2 sequestration monitoring. In this study, a seismic inversion method incorporating linear programming sparse spike inversion (LPSSI) was employed to observe and analyze the CO2 plume in the Sleipner field, Norway. The foundational dataset includes 3D post-stack seismic data from the year 1994, with special emphasis on the monitoring data collected in 1999, following four years of CO2 sequestration. The initial stage involved the equalization of data to guarantee the consistency of seismic traces, particularly beyond the reservoir zone. This was crucial, considering the primary focus on detecting changes in reservoir properties over time. The analysis utilized synthetic data to investigate alterations in seismic amplitude, highlighting that amplitude variations were more prominent compared to variations in velocity and density. Through the cross-equalization process, it was observed that the initial data repeatability was low, indicated by a normalized root mean square (NRMS) value of 0.6508. However, significant improvement was achieved, bringing the NRMS value to a more satisfactory level of 0.5581. This improvement underscored the alignment of features both above and below the reservoir, underscoring the efficacy of the cross-equalization technique. The outcomes of the 4D inversion provided insights into the distribution of CO2 within the reservoir, revealing upward migration. Importantly, the results confirmed the secure storage of CO2 within the reservoir, affirming the integrity of the overlying cap layer. The study offers valuable contributions to understanding reservoir dynamics during production, thereby enhancing our capacity to optimize CO2 storage and implement safe reservoir management practices.Keywords carbon capture and storage (CCS), 4-D inversion, cross-equalization, normalized root mean square (NRMS), seismic data analysis