Thin layer detectability in a growing CO2 plume: testing the limits of time-lapse seismic resolution

Time lapse seismic surveys covering the CO2 injection plume at Sleipner are used to test novel techniques which estimate the thickness of a spreading CO2 layer. Utilising the spectral content of the data, the methods extend the limited vertical resolution encountered with time domain data. Spectral decomposition using the smoothed pseudo Wigner-Ville distribution extracts monochromatic reflection amplitudes from the topmost CO2 layer and is used to assess the lateral variation in peak tuning frequency. This provides a direct proxy for temporal thickness which show consistency with true layer thicknesses derived from structural analysis. A spectral inversion method is also applied to a subset of the upper layer, with limited success. It is noted that high signal-to-noise ratios and the absence of overlying and underlying reflections are required to utilize the technique fully.