Wide Azimuth Reflection Response In 3-D Angle Gathers From OBS Node Data

Wide azimuth seismic data illuminate the subsurface at a wide range of source-receiver azimuths. This valuable azimuthal information may be extracted from seismic data in the form of 3-D angle domain common image gathers (ADCIGs). Residual moveout (RMO) in 3-D ADCIGs generally varies with azimuth when the migration velocity is incorrect. However, to obtain accurate RMO in 3-D ADCIGs wide azimuth seismic data are necessary. Applications of 3-D ADCIGs include seismic interpretation and estimating velocity updates for wide-azimuth velocity tomography. We generate 3-D ADCIGs from wide azimuth OBS node data. OBS node data typically contain relatively fewer seafloor nodes compared to surface sources, but source coverage per node typically samples the full desired range of source-receiver offsets and azimuths. This makes OBS node data ideal for producing 3-D ADCIGs as long as the sampling of receiver nodes is sufficiently dense. Aliasing in ODCIGs caused by large node spacing is a potential problem that can degrade the quality of the ADCIGs. We address this in two ways. We image the downgoing wavefield, which offers wider subsurface illumination and overlap per node than can be obtained from the upgoing wavefield. We also perform anti-alias filtering of the ODCIGs by windowing them in the subsurface offset domain before conversion to 3-D ADCIGs. These steps allow us to obtain high quality 3-D ADCIGs from OBS node data. We demonstrate this using a deep-water OBS node field data set.