The Benefits of Multi-azimuth Depth Migration over the Tidepole Field, North West Shelf, Australia

The Tidepole gas field, located in WA-5-L on the North West Shelf, Australia was discovered in 1971. The field is covered by the high-resolution Demeter 3D seismic survey acquired over the central North West Shelf in 2003, but further appraisal of the Tidepole field remained difficult due to poor seismic data quality. The successful results from model studies led to the acquisition in 2007 of two additional azimuths over the Tidepole field to complement the existing Demeter data. The two new datasets were acquired at azimuths 60 and 120 degrees apart from Tidepole to maximize the azimuthal coverage. Time domain processing of the multi-azimuth data revealed the existence of strong localized velocity differences in the different acquisition directions. To resolve these differences multi-azimuth anisotropic pre-stack depth migration was proposed. During the model building process the conventional residual moveout from all three azimuths was used to perform a multi-azimuth tomography. Initially an isotropic model was used to solve for heterogeneity. Then anisotropic layers were introduced where residual moveout remained. The resulting single model was used to migrate all three azimuths to the same depth. This paper demonstrates the benefits of multi-azimuth depth migration.