Post-stack stratigraphic inversion workflow applied to carbon dioxide storage: application to the saline aquifer of Sleipner field‡

Abstract

A B S T R A C TIn the Norwegian North Sea, the Sleipner field produces gas with a high CO 2 content. For environmental reasons, since 1996, more than 11 Mt of this carbon dioxide (CO 2 ) have been injected in the Utsira Sand saline aquifer located above the hydrocarbon reservoir. A series of seven 3D seismic surveys were recorded to monitor the CO 2 plume evolution. With this case study, time-lapse seismics have been shown to be successful in mapping the spread of CO 2 over the past decade and to ensure the integrity of the overburden.Stratigraphic inversion of seismic data is currently used in the petroleum industry for quantitative reservoir characterization and enhanced oil recovery. Now it may also be used to evaluate the expansion of a CO 2 plume in an underground reservoir. The aim of this study is to estimate the P-wave impedances via a Bayesian model-based stratigraphic inversion.We have focused our study on the 1994 vintage before CO 2 injection and the 2006 vintage carried out after a CO 2 injection of 8.4 Mt. In spite of some difficulties due to the lack of time-lapse well log data on the interest area, the full application of our inversion workflow allowed us to obtain, for the first time to our knowledge, 3D impedance cubes including the Utsira Sand. These results can be used to better characterize the spreading of CO 2 in a reservoir. With the post-stack inversion workflow applied to CO 2 storage, we point out the importance of the a priori model and the issue to obtain coherent results between sequential inversions of different seismic vintages. The stacking velocity workflow that yields the migration model and the a priori model, specific to each vintage, can induce a slight inconsistency in the results.

Dual sensor streamer technology used in Sleipner CO2 injection monitoring

“…In addition we will compare image qualities between the dual sensor streamer and conventional data. Several authors have made estimations of the CO 2 thickness from the conventional seismic data based on a variety of inversion and pre-stack analysis methods of amplitude and time shifts (Ghaderi and Landrø 2009;Queisser and Singh 2010;Evensen and Landrø 2010;Delépine et al 2011;Velis and Rubino 2011;White, Williams and Chadwick 2012;Williams and Chadwick 2012). We show how the improved resolution of the dual sensor streamer data results in improved thickness estimates for the uppermost CO 2 -filled layer in the Utsira Fm at Sleipner, and compare to estimates from the literature.…”

“…If we assume a consistent increase in layer thickness with time, our maximum estimate of 11 m is consistent with these values, as the plume has had four more years of growth since 2006. Delépine et al (2011) performed a post-stack inversion and estimated the thickness of the uppermost sand layer as 10-15 m. Although they do not claim all of this sand to be CO 2 filled in 2006, it must be indirectly assumed, as the repeated 2006 seismic data were used in the estimate. This is significantly higher than other authors' estimates for 2006 and also high compared to what we estimate from the 2010 data, acquired four years later.…”

“…* E-mail: akafu@statoil.com 1 PGS GeoStreamer CO 2 is injected into the Utsira Fm, a saline aquifer at 800-1100 m depth below sea surface. Several authors have made estimations of the CO 2 thickness from the conventional seismic data based on a variety of inversion and pre-stack analysis methods of amplitude and time shifts (Ghaderi and Landrø 2009;Queisser and Singh 2010;Evensen and Landrø 2010;Delépine et al 2011;Velis and Rubino 2011;White, Williams and Chadwick 2012;Williams and Chadwick 2012). Repeated seismic surveys were acquired in 1999, 2001, 2002, 2004, 2006, 2008 and 2010, to monitor the CO 2 .…”

Quantitative Prediction Of Injected CO2 At Sleipner Using Wave-Equation Based AVO

“…This step also calibrates the seismic data with respect to angle-dependent propagation effects in the overburden. While only sonic and gamma-ray were logged genuinely, shear sonic and density were derived following the method by Delépine et. al (2011).…”

Prediction of Elastic Properties Within CO2 Plume at Sleipner Field Using AVS Inversion Modified for Thin‐Layer Reflections Guided by Uncertainty Estimation

“…The CO 2 plume imaged as a number of bright subhorizontal reflections in the time-lapse 3-D seismic data acquired during 1994, 1999, 2001, 2002, 2004, 2006, and 2008 is growing and maturing with time (Arts et al, 2004(Arts et al, , 2008Chadwick et al, 2005Chadwick et al, , 2010Lumley, 2010). The reflections mostly Chadwick et al, 2005;Del'epine et al, 2011). Locations of the preinjection exploration Well 15/9-13 and the deviated CO 2 injection Well 15/9-A-16 are shown by red dots.…”