Imaging

A modern reprocessing sequence has been applied to the full 34 000 sq. km of Santos Vision data. Using advanced processing and imaging techniques the results offer reliable images that limit exploration risk.

Eleven separate surveys have been reprocessed from field tapes, applying the latest 3D designature, deghosting and demultiple processes. The improved preprocessed data were then utilized to build new anisotropic depth velocity models to create a single regional, seamless, set of high-quality broadband depth migrated products covering a large area of the Santos Basin.

This Vision product extracts maximum fidelity from the legacy 3D data, incorporating our latest technologies such as Reverse Time Migration (RTM), Full Waveform Inversion  (FWI) and Least Squares Migration (LSM).

The Key to Good Imaging is a Good Velocity Model

On legacy 3D depth products, the isotropic assumptions used for depth velocity modeling proved unsuitable for the image resolution and depthing required for developing these presalt reservoirs.  Incorporating anisotropic assumptions and Full Waveform Inversion (FWI) improved the accuracy of the depth velocity modeling of these post-salt carbonates, the complexities within the layered evaporite sequence, and the differing character of the post-salt carbonates throughout the area. These geological features need to be carefully understood and incorporated into the depth velocity model building process.  In addition, the presence of areas with good reflectivity and others with little or no reflectivity must be accounted for in the depth modeling to obtain clear images.

A unique implementation of FWI was deployed that included the full wavefield. This FWI pushed deeper than ever before, obtaining robust velocity updates in the presalt section and throughout the entire 34 000 sq.km area.

As demonstrated with the examples below, PGS can deliver high-quality depth imaging using state-of-the-art seismic processing, velocity model building and advanced imaging technologies and workflows.

 

A demonstration of the benefits of reprocessing using PGS 3D deghosting and designature. Pre-migration signal processing enhances the frequency content and provides a sharp wavelet and superior bandwidth.

 

NMO stacks illustrating the benefits of reprocessing with PGS latest demultiple workflows. Residual multiple energy degrades the legacy image and the introduction of an enhanced demultiple sequence provides a clearer image at the pre-salt.

 

This comparison between the legacy and reprocessed Kirchhoff images illustrates some of the improvements provided by the latest reprocessing. The deghosting and designature delivers a sharper wavelet. The enhanced demultiple workflow ensures less residual multiple energy remains and leads to a cleaner section in the deep. A more accurate velocity model provides clear improvements in focusing throughout the section, with a better resolved image at the pre-salt level.

 

An extensive anisotropic velocity model building workflow was implemented during the reprocessing of the Santos data. This included Full Waveform Inversion (FWI) and hyperTomo®, allowing velocity variations to be captured within the shallow overburden, the sedimentary basins and post-salt carbonates, and providing a more accurate picture of the salt bodies and ultimately the pre-salt carbonate plays.

 

PGS LSM corrects for distortions caused by incomplete acquisition and propagation effects, improving amplitude fidelity and resolution of depth migrated images. In the Santos basin it reduces the impact of poor illumination and enhances the vertical and horizontal resolution of the pre-salt image.