Imaging the geology subsalt and at the transition between extra-salt and subsalt has been a challenge at Mad Dog even with extensive seismic data coverage, including two WATS surveys and multiple NATS surveys. WATS acquisition and TTI velocity model processing generated major improvements in the image at Mad Dog. One of the observations of a previous TTI project is the presence of a strong orthorhombic anisotropic effect in a salt mini basin above the field. This finding led to the decision to reprocess the Mad Dog data with a tilted orthorhombic (TOR) velocity model. The main objective of this project is to build an orthorhombic velocity model with nine parameters compared to five with the TTI processing. The TOR anisotropic parameters are generated with the latest FWI and tomography techniques and take guidance from the stress field from a geomechanical model. The outcome of the project is very encouraging with results including better constructive imaging in crucial areas of the field, an incremental increase in signal-to-ratio everywhere and increased fault resolution. The TOR velocity model will be used to migrate a future ocean bottom nodes survey to address some of the remaining imaging challenges.
Presentation Date: Wednesday, October 17, 2018
Start Time: 8:30:00 AM
Location: 208A (Anaheim Convention Center)
Presentation Type: Oral
Fine scale structural and stratigraphic geological features, such as faults and channels, are important in petroleum exploration and production. As surface seismic usually has difficulty in imaging these small (150 feet and smaller) faults and channels in deep subsalt reservoir, we investigate whether high frequency 3D VSP imaging can detect them. We first build a 3D TTI (transverse isotropy with tilted symmetry axis) model with fine scale faults and channels, then generate high frequency (48 Hz) 3D VSP data with TTI finite difference modelling (FDM) and image the data using reverse time migration (RTM). Results show that high frequency 3D VSP data provides high resolution images of these important geological features in the subsalt reservoir.