Wide azimuth data were acquired over Mad Dog field located in the southern Green Canyon area of the Gulf of Mexico. To update the sediment velocities using the additional information that wide azimuth data provides, we chose to sort that data into nominal vector offsets that have both inline and cross-line components. Then, we performed common offset Kirchhoff migration on each vector offset. Then we used multi-parameter moveout image gather tomography to obtain a higher resolution sediment velocity model than we previously had from narrow azimuth data.
We also added an extra iteration to the conventional topdown approach used for salt model building to help better image complexities of the top of salt, such as deep minibasins. In deep mini-basins, in order to image parts of the top of salt, we need rays that travel through salt. To accomplish this, we have picked the top of salt everywhere outside of the deep mini-basins. Then we performed a partial salt flood migration and picked remaining top of salt at the base and flanks of the deep sedimentary basins. This enhanced the quality of the top salt image and made the interpretation of the base and flanks of the mini-basins more reliable.