Mapping reservoir pressure and saturation changes using seismic methods-possibilities and limitations

摘要

In this paper, travel-time and amplitude information from time-lapse seismic data are combined to improve the mapping of an over-pressured reservoir segment. The increased pore pressure is caused by water injection into the segment. According to RFT measurements in the well, the pore pressure increase is of the order of 50 - 80 bars. The observed amplitude increase (between the base line and the monitor survey) associated with the top reservoir event is of the order of 100-200%. A rough estimate of the velocity changes needed (assuming that the density change is negligible) to explain this amplitude change is a 20% reduction in the P-wave velocity. The observed pull-down effect (time-lapse travel-time shift) measured over the whole reservoir thickness is of the order of only 4-6 ms, indicating a gradual change in velocity below the top reservoir event, decreasing with depth.