PZ processing and Imaging
Seafloor recording for enhanced demultiple and unusual acquisition geometries
Ocean-bottom cable 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.
The effective combination of these components can significantly reduce the ghost and water-layer multiple problems (Barr, 1989). 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 surveys, it is important to use an imaging algorithm that can accurately compensate for the different source and receiver datum in marine OBC surveys, and incorporate anisotropy. Our anisotropic prestack time (omega-time pstm) and depth (omega-depth home page) migrations are ideally suited for imaging PZ data in every type of geological setting.
OBC and land acquisition configurations enable recording seismic data across a rich distribution of azimuths. By splitting the data in limited-azimuth cubes, we are able to analyze clear azimuthal variations in P-wave amplitudes.
Related references
- Muijs, R., Holliger, K., and Robertsson, J. O. A., Data-driven adaptive decomposition of multicomponent seabed recordings, 73rd Annual Society of Exploration Geophysicists (SEG) Meeting, Dallas, 2003.
- Brunellière, J., Caprioli, P., Grion, S., Tilling, D., Amundsen, L., Aronsen, H., Surface multiple attenuation by up-down wavefield deconvolution: An OBC case study, EAGE Annual Conference, June 2005
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