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Utilizing spectral decomposition to determine the distribution of injected CO 2 at the Snøhvit Field
Author(s) -
White James C.,
Williams Gareth A.,
Grude Sissel,
Chadwick R. Andrew
Publication year - 2015
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/1365-2478.12217
Subject(s) - amplitude , amplitude versus offset , saturation (graph theory) , geology , regional geology , gemology , offset (computer science) , mineralogy , reflection (computer programming) , engineering geology , hydrogeology , optics , telmatology , seismology , volcanism , physics , geotechnical engineering , mathematics , combinatorics , computer science , tectonics , programming language
Time‐lapse 3D seismic reflection data, covering the CO 2 storage operation at the Snøhvit gas field in the Barents Sea, show clear amplitude and time‐delay differences following injection. The nature and extent of these changes suggest that increased pore fluid pressure contributes to the observed seismic response, in addition to a saturation effect. Spectral decomposition using the smoothed pseudo‐Wigner–Ville distribution has been used to derive discrete‐frequency reflection amplitudes from around the base of the CO 2 storage reservoir. These are utilized to determine the lateral variation in peak tuning frequency across the seismic anomaly as this provides a direct proxy for the thickness of the causative feature. Under the assumption that the lateral and vertical extents of the respective saturation and pressure changes following CO 2 injection will be significantly different, discrete spectral amplitudes are used to distinguish between the two effects. A clear spatial separation is observed in the distribution of low‐ and high‐frequency tuning. This is used to discriminate between direct fluid substitution of CO 2 , as a thin layer, and pressure changes that are distributed across a greater thickness of the storage reservoir. The results reveal a striking correlation with findings derived from pressure and saturation discrimination algorithms based on amplitude versus offset analysis.