Technical Library

Improving the Prospectivity of Sub-basalt Geology with Elastic FWI Imaging

Jyoti Kumar, Matthew Hart, Bent Kjølhamar, Wonkee Kim, Stuart Fairhead — Wed, 22 Oct 2025 03:02:02 GMT

In this paper we apply an acoustic and elastic FWI Imaging approach to the difficult problem of
improving sub-basalt prospectivity. FWI Imaging is rapidly becoming a key deliverable in
any imaging and velocity model building workflow. It can be seen as a non-linear least-squares migration with the images being generated almost as a by-product of the model building approach. It allows for greater understanding of complex geology where typical migration images may have limitations and as such, is an invaluable guide for any interpretation
work.

Northern Pelotas Basin: Stratigraphy and Basin Development

P. Zalan, K. Reuber, H. Houllevigue — Wed, 15 Oct 2025 18:30:18 GMT

The underexplored region of the northern Pelotas Basin, Southeast Brazil is gaining attention
due to a series of discoveries on the African margin. Conjugate discoveries to the Southern
Pelotas region have translated to renewed interest in the greater area. The area of Northern
Pelotas sits south of the Santos Basin salt province containing a mix of features between the
two depositional settings. Newly acquired 3D seismic data reveal volcanic basement structure
and complex overlying stratigraphy. In this study, we assess the correlation of regional events
leading to the crustal deformation and evaluate the hydrocarbon prospectivity of the
stratigraphic overburden units using available well data points and seismic facies.

Elastic FWI Unlocks Complex Geology: Advancing Streamer-based Imaging Offshore Brazil

J. Burren, B. Bianchi, F. Sotero, G. Jangelme — Wed, 15 Oct 2025 18:26:38 GMT

Offshore Brazil comprises a diverse set of geological provinces, from the deepwater salt provinces of the Santos and Campos Basins to the less mature, structurally complex Equatorial Margins. Despite differing in tectonic history and depositional environments, these regions share common imaging challenges – strong impedance contrasts, stratigraphic heterogeneity, and complex salt or carbonate bodies – that hinder conventional velocity model building (VMB) workflows. While acoustic full-waveform inversion (aFWI) has proven useful for refining models, its simplifying assumptions often limit its effectiveness in these geologically demanding settings. This paper explores the application of elastic full-waveform inversion (eFWI) to towed-streamer datasets, demonstrating it can deliver meaningful improvements in subsurface velocity models across Brazil’s offshore basins using typical legacy seismic data that is abundant in the region.

Streamlining Marine Seismic Preprocessing with AI

M. Roberts, O. Brusova, D. Brookes, S. Baldock, A. Valenciano — Wed, 15 Oct 2025 18:17:48 GMT

In seismic imaging, reducing the turnaround time of imaging projects is essential. Machine
learning solutions offer the potential of reduced turnaround time without the loss of data quality
that comes with traditional fast-track solutions. These are achieved through faster execution times and the elimination of parameter testing. Machine learning solutions have been used to reduce turnaround in the VMB (Velocity Model Building) steps (Crawley, 2024) and in the preprocessing steps (Brusova, 2021; Roberts, 2024). Here, we leverage machine learning (ML) to accelerate and improve the efficiency of preprocessing, focusing on three key steps: swell noise removal, deghosting, and designature. We demonstrate these results on data from a recent 3D project from the Niger Delta, offshore Nigeria.

Assessing the Exploration Potential of Mid-Upper Cretaceous Sedimentary Fairways of Equatorial Brazil

P. Zalan, K. Reuber, H. Houllevigue — Wed, 15 Oct 2025 18:13:16 GMT

Recently refocused exploration interests in the Equatorial basins of Brazil have highlighted the
deepwater potential for the region. Drilling results from the Anhangá deepwater well in 2024
highlights the potential of a deeper early drift and passive margin hydrocarbon kitchen in the
region. In this study we focus on the Mid and Late Cretaceous stratigraphic sequences of the
equatorial basins between the St Paul and the Four-North Fracture Zones. These sedimentary
basins cover approximately 100,000 km2, with water depths from 100 meters to greater than
4,000 meters. Seventy percent of the basin has water depths greater than 1,500 meters and is
largely un-explored for oil and gas. To date, the 2011 Harpia Pama discovery, confirming the
prospectivity of a distal kitchen, is the only well to test the deepwater region. Seismic data from
the deepwater basins of Brazil’s Equatorial Margin record a widely varied history of stratigraphic
infill. Mapped and interpreted seismic data reveal extensive play fairways here that have
analogous features to discoveries made on the conjugate margin of Equatorial Africa.

Estimating Subsurface Properties with Angle-Domain Multi-parameter FWI

N. Chemingui, S. Crawley — Wed, 15 Oct 2025 18:08:14 GMT

We present a multi-parameter Full Waveform Inversion (MP-FWI) strategy designed to enhance
reservoir characterization by jointly inverting for P-wave velocity and angle-dependent reflectivity. The formulation exploits the distinct sensitivities of seismic traveltimes and amplitudes to decouple low- and high-wavenumber components of the model, improving the recovery of subsurface properties critical to prospect evaluation.

An OBN Multi-Parameter FWI Case Study from Santos Basin

J. Burren, E. Frugier, Ø. Korsmo (TGS) — Wed, 15 Oct 2025 18:02:54 GMT

A multiparameter inversion workflow that jointly estimates velocity and reflectivity was applied to an ocean bottom node (OBN) dataset from the deep-water Santos Basin, offshore Brazil. The
complex geology—featuring layered evaporites above pre-salt reservoirs—poses significant
imaging challenges due to salt-related illumination issues and resolution loss. Starting from minimally processed hydrophone data, the inversion improved structural imaging and amplitude fidelity by integrating velocity modeling and least-squares migration in a unified framework. The results highlight the workflow’s value in resolving subsurface complexity and informing exploration and reservoir development in pre-salt environments

Campos Basin 4D study. A Case Study Integrating Conventional Hydrophone and Multi-sensor Towed Streamer for Monitoring the Albacora Leste Field

Wed, 15 Oct 2025 17:56:58 GMT

In this 4D case study, conducted in the Campos Basin, Brazil, we demonstrate that is possible to
extract reliable field production information with relaxed constraints on the acquisition
repeatability. We show how different streamer technology datasets can be combined to monitor
the production of the Albacora Leste field. The aim is that the 4D study will provide additional
reservoir production information on fluid saturation and pressure changes. This “opportunistic”
Albacora Leste 4D case study combined a 2005 Multi-Client Baseline dataset, acquired with
shallow towed conventional hydrophone streamer, with a 2022 Monitor dataset acquired with
deep towed multi-sensor streamer. One of the 4D imaging challenges was to accommodate the
two types of streamer and non-repeated shot positions for computing an accurate 4D signal.
Through specific 4D processing sequences and a 4D Least-Square Kirchhoff imaging approach,
we succeeded in improving the seismic signal resolution and were able to detect consistent fluid
saturation and pressure changes within thin sandstone layers in the reservoirs. The 4D Albacora
Leste project has enabled us to map and better understand the longstanding production of this
complex and compartmentalized reservoir composed of turbiditic stacked channels with the aim
of identifying new development opportunities.

Advancing Complex Subsalt Imaging Using Elastic FWI and Sparse Ocean-Bottom Node Acquisition

H. Xing, R. Huang, F. Liu, Y. Li, C. Macesanu, C. Westbrook, M. Hegazy — Wed, 15 Oct 2025 17:50:02 GMT

This study highlights the effectiveness of Elastic Dynamic Matching FWI (E-DMFWI) using sparse
OBN data to enhance subsalt imaging in the Gulf of Mexico. Leveraging ultra-long offset, full-azimuth, and low-frequency data from Amendment Phase 1 and Phase 2, E-DMFWI accurately
resolves salt feeders, carbonates, and deep Luanne salt, and improves imaging beneath complex shallow salt where illumination was previously poor with the streamer data. The approach delivers superior imaging and has the potential to greatly enhance project efficiency.

Mitigating Structural Uncertainty: Early Insights from OBN FWI Imaging - A Santos Basin Case Study

Wed, 15 Oct 2025 16:39:12 GMT

Full Waveform Inversion (FWI) yields high-fidelity velocity models for enhanced seismic imaging
in complex geological settings. FWI-Derived Reflectivity (FDR) offers rapid subsurface reflectivity reconstruction with improved illumination and turnaround over conventional methods. In structurally complex areas, high-quality seismic data are crucial for FWI. Ocean Bottom Node (OBN) data—characterized by rich low-frequency content, long offsets, and broad azimuth coverage—significantly enhances the resolving power of Full Waveform Inversion (FWI) for building accurate velocity models. The resulting FDR images exhibit higher resolution and
improved illumination, providing clearer imaging and reduced structural uncertainty compared to
Multi-Azimuth (MAZ) datasets, and enabling more reliable geological interpretation. This Santos
Basin case study highlights a significant reduction in structural uncertainty by integrating OBN
data with an FWI imaging workflow.