MULTIDOMAIN ANALYSIS AND WAVE-FIELD SEPARATION OF CROSS-WELL SEISMIC DATA

While cross-well traveltime tomography can be used to image the subsur face between well pairs, the use of cross-well reflections is necessar y to image at or below the base of wells, where the reservoir unit is often located. One approach to imaging cross-well reflections is to tr eat each cross-well gather as an offset VSP and perform wavefield sepa ration of direct and reflected arrivals prior to stacking or migration . Wavefield separation of direct and reflected arrivals in VSP is acco mplished by separating the total wavefield into up and downgoing compo nents. Since reflectors can exist both above and below the borehole wa vefield, separation of cross-well data into up- and downgoing componen ts does not achieve separation of direct and reflected arrivals. In ou r technique, we use moveout filters applied in the domain of common ve rtical source/receiver offset to extract reflected arrivals from the c omplex total wavefield of a cross-well seismic data set. The multiple domains available for filtering and analysis make cross-well data more akin to multifold surface seismic data, which can also be filtered in multiple domains, rather than typical VSP data, where there is only o ne domain (common source) in which to filter. Wavefield separation of cross-well data is shown to be particularly effective against multiple s when moveout filters are applied in common-offset space.