A case study in seismic diffraction near a Gulf Coast salt dome

Abstract

The diffraction response from a sequence of truncated dipping beds is examined. It is shown that standard velocity analysis and interpretation can emphasize the diffracted energy in the common‐depth‐point (CDP) stack. This energy can then produce a distorted image in the poststack migration of the data. In our case this distortion took the form of smaller estimates for the structural dip, which was independently confirmed by well control. Wave‐equation synthetics are also used to support the role of truncated dipping beds as strong diffractors. It is shown that the diffraction from these beds will give rise to certain identifiable characteristics in the CDP data. These characteristics are demonstrated by examining the ideal case of a truncated reflector with dip. It is shown that in the presence of dip, a proper choice for the stacking velocity will lead to the enhancement of the reflected energy at the expense of the diffraction. These stacking velocities can then be used to improve the interval velocity estimates for migration. In this study the application of these ideas brought the structural dip as derived from the surface seismics into good agreement with the well data. In comparison with model data, there was also some evidence that the gas‐water contact could be identified in the reprocessed migration.