Sub‐salt exploration in the deepwater Gulf of Mexico: Integrating potential field and seismic data to predict the location of salt‐cored antiforms below the Wilcox Formation.

Abstract

The deepwater Gulf of Mexico Wilcox sub‐salt play requires a regional, structural and stratigraphic context in order to better understand sediment distribution, salt geometry, basement architecture and basement composition. However, the presence of the thick Louann allochthonous salt canopy has long been the main deterrent to exploration and is still one of the key risks associated with the play. When using seismic data alone, the fundamental problem is sub‐salt seismic imaging and it remains a key challenge for seismic processors. Even with the latest seismic acquisition technologies, such as wide azimuth and sea‐bottom node surveying, a clear sub‐salt image is still very difficult to achieve. It is therefore important to utilize other geophysical data to help our understanding of the sub‐salt environment and this can be achieved through integration of seismic, gravity and magnetic data. As a result of detailed and methodical integration, a new basement map has been created from high‐resolution aeromagnetic data and Pre Stack Depth Migrated (PSDM) seismic data. With this new surface, it has been possible to carry out detailed quantitative 2D and 3D earth modeling. A number of new workflows have been developed to predict the spatial distribution of both the shallow and deep allochthonous salt canopies, basement density and susceptibility variations, the location of open salt feeders to the shallow allochthonous salt canopy and the location of the continental‐oceanic boundary (COB). Qualitative sub‐salt interpretation has also been used to ground truth the results of the modeling. This was achieved by removing the gravity signal attributed to the shallow allochthonous salt canopy to leave a residual gravity map of the sub‐salt geology. Enhancing this residual enabled the location of gravity anomalies, interpreted as related to salt feeders, deep allochthonous salt‐cored antiforms, basement geometry and crustal composition. When combined, these qualitative and quantitative techniques have allowed a better understanding of the sub‐salt environment. In particular, results using the new integrated 3D modeling workflow, demonstrate that salt‐cored antiforms have been predicted beneath 90% of the drilled sub‐salt Wilcox wells. Creating a deep allochthonous salt isopach has identified many other structures.