Application of offshore 3D dual-azimuth seismic data processing to the Panyu 4 Sag

The study area, Panyu 4 Sag, occurs in the northern part of the Pearl River Mouth Basin where Neogene NWW-strike normal faults are well developed. The traps on the upside of those faults are important targets for hydrocarbon exploration. However, the first round of 3D seismic data of this area, which is parallel to the direction of fault strike, provides poor images in fault shadow zones, with low signal-to-noise ratio, abnormal event dropping down and strong structural distortion. Thus traps on the upside of normal faults always bear structural uncertainties in data interpretation. For this reason, a second round of 3D seismic is performed vertical to fault strike and fault shadow imaging is improved compared to the first round of 3D seismic. In order to further improve the fault shadow imaging, the dual-azimuth processing considering azimuthally anisotropic is employed using both of the 3D seismic datasets. The core of the dual-azimuth processing is the dual-azimuth anisotropic PSDM. By comparison of the dual-azimuth anisotropic PSDM results and the PSDM results using either of the single azimuth, it is found that the seismic data which is acquired vertical to the fault strike is more suitable for fault shadow imaging. What’s more, the dual-azimuth data shows the best illumination in fault shadow, as well as the highest signal-to-noise ratio. The reliability of the dual-azimuth data is demonstrated by the drilling results of the evaluation wells in the fault shadow zone. At the same time, some references on seismic acquisition design and data processing flow can be provided for solving the imaging problem of fault shadow zone in similar areas.