The operational condition that dominates the survey planning and implementation is the presence of major shipping transit fairway to and from the Suez Canal. This shipping thoroughfare covers about 70% of the survey area. Operational considerations necessitate a shooting orientation that closely parallels the shipping lanes, which approximates the strike direction of the subsurface target. Shooting in the dip direction, across the shipping lanes, was not considered to be operationally feasible for a 3D spread or operation. Wave equation simulation was used in preparation of the acquisition program specifications. The technique was utilized to produce synthetic seismogram shot records that were in turn examined, interpreted and processed to assess the impact of various parameter combinations on meeting technical, operational and economic requirements set by the exploration staff.
The implementation of new recursive operators for computation of numerical derivatives results in minimal dispersion in Reverse Time Migration Prestack Depth Migration (i.e. RTM PSDM). Compared to the more commonly used finite difference operators, the presented new method enables imaging of higher frequencies in RTM PSDM. Since RTM PSDM is the modern method of choice for imaging many exploration targets, computer optimization is an integral part of code development. We present here details of the GPU implementation for newly developed spatial derivative operators which enable routine use in industrial settings.
With readily available wide-azimuth, onshore, 3D seismic data, the search for attributes utilizing the azimuthal information is ongoing. Theoretically, in the presence of ordered fracturing, the seismic wavefront shape changes from spherical to nonspherical with the propagation velocity being faster parallel to the fracturing and slower perpendicular to the fracture direction. This concept has been adopted and is used to map fracture direction and density within unconventional reservoirs. More specifically, azimuthal variations in normal moveout velocity or migration velocity are often used to infer natural fracture orientation. Analyses of recent results have called into question whether azimuthal velocity linked to intrinsic azimuthal velocity variations can actually be detected from seismic data. By use of 3D orthorhombic anisotropic elastic simulation, we test whether fracture orientation and intensity can be detected from seismic data. We construct two subsurface models based on interpreted subsurface layer structure of the Anadarko Basin in Oklahoma. For the first model, the material parameters in the layers are constant vertically transverse isotropic (VTI) in all intervals. The second model was constructed the same way as the base model for all layers above the Woodford Shale Formation. For the shale layer, orthorhombic properties were introduced. In addition, a thicker wedge layer was added below the shale layer. Using the constructed model, synthetic seismic data were produced by means of 3D anisotropic elastic simulation resulting in two data sets: VTI and orthorhombic. The simulated data set was depth migrated using the VTI subsurface model. After migration, the residual moveouts on the migrated gathers were analyzed. The analysis of the depth-migrated model data indicates that for the typical layer thicknesses of the Woodford Shale layer in the Anadarko Basin, observed and modeled percentage of anisotropy and target depth, the effect of intrinsic anisotropy is too small to be detected in real seismic data.
The Tempest 3D model and dataset were generated to test industry's ability to correctly image deep water Gulf of Mexico subsalt structures. The project included four steps: (a) design of a 3-dimensional model based on real Gulf of Mexico geology; (b) acquisition design that included narrow azimuth, mid (range) azimuth and wide azimuth geometries; (c) numerical simulation using twoway wave equation algorithm and construction of three synthetic datasets; (d) application of various prestack depth migration algorithms for testing of subsalt imaging quality. The project parameters acquisition design and prestack depth migration algorithm parameters were all selected based on a single guideline: to be done as close as possible to field data acquisition and imaging. By following this guideline we obtained a dataset which realistically represents our ability to resolve subsalt imaging challenges. In this paper we present the project steps and demonstrate its main results.
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