PZ Processing and Imaging

Seafloor recording for enhanced demultiple and unusual acquisition geometries

Ocean bottom cable (OBC) acquisition has several advantages. Although the majority of OBC processing flows closely mirror those of a conventional processing sequence, several steps require special attention.

PZ summation and calibration

The receiver ghost and water-layer multiples generate notches in the seismic bandwidth that are dependent on the two-way traveltime through the water. These can present significant limitations to conventional towed-marine seismic imaging and can be reduced with careful processing of the multicomponent data.

Positioning of multicomponent sensors on the seabed presents an opportunity to reduce the receiver ghost and water-layer reverberation sequence because of the difference in the behavior of the pressure wave and the particle displacement on the seabed. The hydrophone records only the scalar pressure response and does not distinguish between up and down wavefields. The geophone records the vector displacement of the seabed that is different for the up and down wavefield.

P stack has been effectively deghosted by PZ combination.

After stack, the strong water layer multiple emanating from top and base of salt on the hydrophone only stack (left) has been effectively deghosted by PZ combination—even over the steep dips of the salt flank.

The effective combination of these components can significantly reduce the ghost and water-layer multiple problems. WesternGeco has a number of proprietary and industry-accepted methods to calibrate and combine the PZ data in different conditions.

PZ imaging

Migrating PZ data requires a similar workflow to that of conventional imaging techniques. However, for long-offset and wide-azimuth (WAZ) surveys, it is important to use an imaging algorithm that can accurately compensate for the different source and receiver data in marine OBC surveys and incorporate anisotropy. Our anisotropic prestack time and depth migrations are ideally suited for imaging PZ data in every type of geological setting.