The Rainbow B pool, a carbonate reservoir, is undergoing solvent and gas injection to extract the remaining oil. Although not commonly done because the expected seismic changes are small, time-lapse or 4D processing and interpretation are applied to two sets of 3D data to detect the locations of the injected fluids. The presence of gas and solvent were best interpreted with the time-delay results, as opposed to the amplitude change results. Fluid related changes were detected in vuggy or low pore aspect ratio porosity zones but changes were not detectable in zones with intergranular porosity. Because the reservoir is extremely heterogeneous and the pore geometry greatly affects the results, this study could detect changes in some but not all locations of the reservoir. This study also showed that the Gassmann equation underpredicts velocity changes in this reservoir. Also, the seismic time-delay results matched the engineering simulation data fairly well.
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