Discrimination between pressure and fluid saturation changes from time-lapse seismic data

Explicit expressions for computing saturation- and pressure-related changes from time-lapse seismic data have been derived and tested on a real time-lapse seismic data set. Necessary input is near- and far-offset stacks for the baseline seismic survey and the repeat survey. The method has been tested successfully in a segment where pressure measurements in two wells verify a pore-pressure increase of 5 to 6 MPa between the baseline survey and the monitor survey. Estimated pressure changes using the proposed relationships fit very well with observations. Between the baseline and monitor seismic surveys, 27% of the estimated recoverable hydrocarbon reserves were produced from this segment. The estimated saturation changes also agree well with observed changes, apart from some areas in the water zone that are mapped as being exposed to saturation changes (which is unlikely). Saturation changes in other segments close to the original oil-water contact and the top reservoir interface are also estimated and confirmed by observations in various wells.