Ganyuan Xia

Multiple Attenuation Methods For Wide Azimuth Marine Seismic Data

Recent advances in wide azimuth marine seismic acquisition, such as Wide Azimuth Towed Streamer (WATS, see Threadgold et al. 2006), offer unprecedented data with a wide range and dense sampling of azimuths and offsets. These relatively expensive surveys were driven primarily by the realization that traditional narrow azimuth towed streamer (NATS) data has inherent deficiencies in illuminating the reservoir under complex structures such as salt.

Processing of a novel deepwater, wide-azimuth node seismic survey

In the fall of 2005, BP commissioned Fairfield Industries to conduct a large, wide-azimuth survey over Atlantis Field in deepwater Gulf of Mexico. The purpose of the survey was wide-azimuth, subsalt imaging using P-waves. The seafloor topography is complex with scoured furrows at the base of the escarpment. A shallow salt body covers a large part of the survey area and rafts the seafloor at the escarpment, leading to very strong velocity contrasts. The water depth in the area varies from approximately 1300 m above the Sigsbee escarpment to 2200 m below it.

Case Study: A Large 3D Wide Azimuth Ocean Bottom Node Survey In Deepwater GOM.

In the fall of 2005 Fairfield Industries was the primary contractor of a large, wide azimuth survey (Ross and Beaudoin, 2006) for BP over the Atlantis field in the deepwater GOM. The water depth in the area varied from approximately 1400 metres to 2300 metres. The survey used 902 four-component ocean bottom nodes (Mitchell and Grisham, 2006), which BP commissioned Fairfield to build. The purpose of the survey was wide azimuth, subsalt imaging using P-waves (Beaudoin and Michell, 2006).

Combining free-surface multiple attenuation with wavefield continuation to attenuate 3D free- surface multiples on multi-component ocean-bottom seismic data

Summary We present a method for attenuating 3D free-surface multiples from multi-component ocean-bottom seismic data. The method (i) has as its input only an ocean-bottom data set, (ii) reduces the need to interpolate data prior to multiple prediction, and (iii) can accommodate an oceanbottom with irregular bathymetry. Similar to free-surface multiple removal methods developed for streamer data, this method is independent of the earth below the oceanbottom. The three-step methodology consists of a 3D multiple prediction step for multi-component receivers and effective sources on the ocean-bottom. The next step uses a wavefield continuation to redatum the sources of the original multiple contaminated data set from the freesurface to the ocean-bottom so that the predicted multiples can be properly subtracted. The last step consists of interpolating the sparsely sampled effective ocean-bottom sources to the grid of the redatumed sources. However, the interpolation can be performed after the multiple prediction resulting in a significant cost saving.

Impact of feathering on imaging for wide azimuth data

Wide azimuth towed streamer data yield improved depth migrated images thanks to additional cross-line offset coverage. The range of cross-line offsets required to reach an optimal image quality may be assessed by carrying out synthetic studies. Such numerical experiment typically contains regular sampling of inline and cross-line offsets and does not reflect realistic field geometry such as streamer cable feathering. We carried out a synthetic experiment that accounts for the effect of cable feathering during the acquisition. The results indicate that cable feathering has little impacts on depth imaging, at least for data frequencies up to 12 Hz at which the experiment was carried out.

Wide Azimuth Anisotropic Imaging At Tubular Bells Field In the Gulf of Mexico

BP, with co-owners Chevron and Hess, acquired a Wide Azimuth Towed Streamer (WATS) survey over the Tubular Bells field in the deepwater Gulf of Mexico to address challenges of imaging subsalt reservoirs. Finite-difference modeling shows that we need to incorporate anisotropy to properly image subsalt reservoirs at Tubular Bells. We present the processing and model building work flow; in particular, how we use Reverse Time Migration (RTM) to image steep dips that results in a better velocity model. The final migrated dataset provides a significant improvement in image quality over the conventional narrow azimuth (NATS) data, and is being used to reinterpret the area.