Monitoring fluid injection using time-lapse analysis: a Rainbow Lake case study

Hannah T. Ng, Laurence R. Bentley, Edward S. Krebes

The Rainbow B pool, a carbonate reservoir, is undergoing gas and solvent injection to extract the remaining oil. Although not commonly done because the expected 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 the vuggy or a crack-like low pore aspect ratio area but changes were not detectable in the intergranular area even though there may be the same amount of fluid present. Because the reservoir is extremely heterogeneous and the pore geometry greatly affects the results, this study could detect changes but not detect the amount of fluid present nor detect bypassed oil. This study also confirmed that the Gassmann equation underpredicts velocity changes. The seismic time-delay results matched the engineering simulation data fairly well.