To overcome the geological challenges and support exploration across the Campos Basin, TGS launched a comprehensive seismic campaign. This initiative combines the rejuvenation of legacy seismic data with the acquisition of new long-offset data.

A modern reprocessing sequence has been applied to the entire 49,000 sq. km. Santos Vision dataset.

Minimize Exploration Risk with
High-Quality Imaging in the Santos Basin

Advanced processing and imaging techniques deliver reliable images that limit exploration risk.

Thirteen 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 pre-salt section and throughout the entire 49,000 sq.km. area.

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

Before Image After Image
A demonstration of the benefits of reprocessing using TGS 3D deghosting and designature. Pre-migration signal processing enhances the frequency content and provides a sharp wavelet and superior bandwidth.
Before Image After Image
NMO stacks illustrating the benefits of reprocessing with TGS' 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.
Before Image After Image
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.
Before Image After Image
Without LSM
With TGS LSM
TGS 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.
Before Image After Image
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.

Campos Basin Imaging

The geology of the Campos Basin (shown in the seismic section below) presents challenges to achieving robust seismic data quality. Whilst the sedimentary overburden is structurally benign, the presence of mass transport complexes (MTC’s) requires the development of a detailed velocity model to resolve. Deeper in the section, Albian carbonate units overlie a layered evaporitic sequence which can vary from completely welded out to significant diapirs which are overhanging in some locations. The main prospective target interval for this survey occurs as carbonate build-ups in the presalt section.

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A vertical seismic section through the Campos Deepwater GeoStreamer X dataset. This image demonstrates the presence of thick syn-rift sediments deposited over a highly faulted basement. Some of these faults may serve as fluid migration pathways to carbonate buildups that have formed atop basement-related structural highs. The regionally extensive Albian salt provides sealing capability for the presalt petroleum system.

Tailoring Acquisition to Deliver Azimuthal Coverage

Most of the survey area is covered by legacy 3D seismic dating back to the early 2000s. Typically, the legacy surveys were acquired in an east-west orientation using a dual vessel Continuous Long Offset (CLO) approach giving a maximum offset of 8,300 m. To provide better spatial and azimuthal sampling and longer offsets, a new second azimuth was acquired in a north-south orientation in 2020 and 2021.

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Rose plot showing the offset and azimuth distribution of Campos GeoStreamer X survey. Adding the new long-offset N-S dataset to the existing E-W surveys better illuminates the presalt targets that are of primary interest.

The new north-south azimuth was acquired with TGS’ proven GeoStreamer broadband technology. Leveraging the impressive towing capabilities of the Ramform Titan-class vessels, a spread of 14 cables x 100 m separation x 10 050 m length was deployed. This configuration set new industry records for overall spread dimensions and for the total amount of cable deployed by a single vessel in Brazil. While delivering the long-offset data needed to image the pre-salt targets, the configuration minimized the number of shot points per square kilometer, reducing any potential for environmental impact. The azimuthal coverage of the combined surveys can be seen in the rose plot above.

Imaging Workflows Customized For GeoStreamer X

The data quality of the Campos Deepwater GeoStreamer X dataset has been optimized using a comprehensive processing and imaging strategy, as demonstrated by the comparison with the legacy data below. The legacy data has been enhanced using a 3D deterministic deghosting approach to replicate the wavelet fidelity achieved from the new broadband GeoStreamer data. Removing unwanted surface ghost effects from both azimuths enabled subsequent processing, such as demultiple, to be applied effectively yet robustly, thereby extracting maximum resolution from the data. The enhanced resolution supports accurate interpretation and reduced uncertainty when assessing prospectivity across the target intervals.

 
Before Image After Image
This comparison between the legacy and GeoStreamer X Kirchhoff images illustrates some of the improvements provided by the additional azimuth and 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 presalt level.

The velocity model has been developed using advanced anisotropic approach which captures detail across the stratigraphic intervals. High-resolution wavelet tomography (TGS hyperTomo) was utilized in a dual-azimuth sense to construct a robust long-wavelength background velocity model. The Albian carbonate units and layered evaporite sequences were accurately interpreted benefitting from improved wavelet resolution, demonstrated in the depth slice below, to correlate units. Leveraging the robust background velocity trend, the model was enhanced to high wavelength utilizing Full Waveform Inversion (FWI), as seen in the comparison below. The multiazimuth, long-offset data further aided velocity model optimization.

Before Image After Image
The application of FWI has significantly improved structural consistency at the base salt and underlying pre-salt intervals. After FWI, the presalt has significantly less model-induced undulations which are resolved to give confidence in the presalt domain.

Supporting Block Nominations

The Campos Deepwater GeoStreamer X dataset can provide Kirchhoff Migration and also Reverse Time Migration products. These complementary migration technologies both deliver amplitude-preserved prestack image gathers to support quantitative interpretation workflows in addition to structural analysis. TGS investigation across the dataset has identified amplitude-supported anomalies that have analogies to known discoveries within the area. We utilized this analysis to support new block nominations, which ANP has since announced will be taken forward as offered acreage in upcoming license rounds.

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