Depth seismic imaging using reflection and first arrival traveltime tomography: Application to a deep profile across the Northern Emirates Foothills

Abstract

Among seismic processing methods, the reflection tomography is performed to compute accurate velocity models for depth seismic imaging and the first arrival tomography is used to determine the complex velocity variations of the structured overburden. In foothills, where reflection tomography suffers from severe limitations, combining these two methods provides a more complete determination of the velocity model from the shallowest zones down to the deeper zones. This combined method has been applied to a deep seismic profile acquired across the Northern Emirates Foothills. The main objective of this study is to acquire new information on deep target structures for hydrocarbon exploration. In the western part, with sand dune on surface, the reflection tomography was successfully applied providing an accurate depth estimation of the carbonate platform, the potential reservoir. In the central foothills part of the profile, the velocity model was computed by joint inversion using the first arrivals down to 4 km depth and the reflected travel times for deeper layers. In the eastern part of the profile, due to the outcropping of the Semail ophiolite, the deep reflection events are not visible and only the first arrival tomography using the long offset traces (±15,000 m) has been applied to determine the ophiolite velocity and the limits of the high velocity contrast (up to 5.5 km/s) which could relate to the top of the underthrust platform and basinal Mesozoic unit. Finally seismic imaging combining joint traveltime tomography and pre-stack depth migration has provided new depth seismic images of the structural features of the complex overburden and of the frontal triangle zone.