Subsalt exploration in shallow waters of the Republic of Congo
Author: Pierre Le Barbanchon, Tony Martin, Mark Martin, Louis Andzouono, Jean Pierre Saba, Alain Richard N’Gouala Nzoussi
First Break - 1 March 2019
The authors reveal new subsalt hydrocarbon potential on the Congo Shelf using modern broadband imaging techniques applied to multi-vintage seismic data.
Long-wavelength FWI updates in the presence of cycle skipping
Author: Jaime Ramos-Martínez, Lingyun Qiu, Alejandro A. Valenciano, Xiaoyan Jiang, Nizar Chemingui
The Leading Edge - 1 March 2019
Full-waveform inversion (FWI) has become the tool of choice for building high-resolution velocity models. Its success depends on producing seamless updates of the short- and long-wavelength model features while avoiding cycle skipping. Classic FWI implementations use the L2 norm to measure the data misfit in combination with a gradient computed by a crosscorrelation imaging condition of the source and residual wavefields. The algorithm risks converging to an inaccurate result if the data lack low frequencies and/or the initial model is far from the true one. Additionally, the model updates may display a reflectivity imprint before the long-wavelength features of the model are fully recovered. We propose a new solution to this fundamental challenge by combining the quadratic form of the Wasserstein distance (W2 norm) for measuring the data misfit with a robust implementation of a velocity gradient. The W2 norm reduces the risk of cycle skipping, whereas the velocity gradient effectively eliminates the reflectivity imprint and emphasizes the long-wavelength model updates. We illustrate the performance of the new solution on a field survey acquired offshore Brazil. We demonstrate how FWI successfully updates the earth model and resolves a highvelocity carbonate section missing from the initial velocity model.
Revitalizing seismic data with new imaging solutions to positively impact field development
Author: Gareth Venfield, Michael Townsend, Paul Cattermole, Tony Martin, Stuart Fairhead
The Leading Edge - 1 January 2019
Evaluating, planning, and forecasting are integral parts of asset development and continue throughout the life cycle of a producing field. The right decisions are required to lower risk and maximize economic recovery in challenging environments. The Claymore Complex is located in the North Sea and was discovered in 1977. A number of geologic challenges affect the imaging and hence field development including a system of shallow interweaving Quaternary channels, numerous high-contrast layers of varying composition, overburden structural complexity, and a sequence of tilted fault blocks containing the main reservoir systems. Historically, seismic processing over the area has not fully solved these challenges, resulting in significant imaging uncertainty. The Claymore Complex has an abundance of data including a large population of well information and interpretation. As part of a data revitalization process, geostatistical integration of these auxiliary data into a velocity model building sequence using full waveform inversion and wavelet shift tomography enabled the generation of an accurate high-resolution velocity model. Access to a recent 3D survey acquired obliquely to existing data improved subsurface illumination for both the model building and imaging phases. Near-surface imaging effects and their impact on reservoir positioning and clarity were improved using the upgraded velocity model and dual-azimuth data. Shallow imaging challenges were mitigated by utilizing the additional illumination and angular diversity contained within the multiple reverberations. The revitalization of the Claymore area seismic data has challenged the current understanding of the geologic framework. Confidence has been improved by solving depth conversion problems and increasing the understanding of fault positioning and reservoir connectivity, which are invaluable for future field development.
SEG 2018: Five Key Takeaways
Author: Andrew Long
Industry Insights - 19 December 2018
Five key topics arising from SEG 2018 that are particularly relevant to marine towed streamer seismic are outlined in this insight: Marine source strategies are evolving, marine vibrators are back, survey efficiency and environmental management go together, multisensor streamers are now accepted industry best practice,
collaboration is the future of R&D.
Barents Sea - A First Look at New High Resolution 3D Multicomponent Seismic
Author: Rune Sakariassen, Nicola O’Dowd, Sören Naumann
GeoExpro - 10 December 2018
The far south-west Barents Sea is one of the few remaining frontier basins. There is little exploration activity and the data coverage is sparse. Until now, almost all existing seismic data was 2D, of variable data quality and as a result, the geology and hydrocarbon potential of the area is not fully understood.
PGS has now covered parts of this area with the first 3D GeoStreamer MultiClient broadband seismic dataset to enhance the geological understanding of the area and as a tool for unlocking new potential in this virtually unexplored and exciting part of the Norwegian Barents Sea. Through advances in data acquisition and imaging, and building on experience of acquiring data in the Barents Sea, this newly acquired dataset illuminates the geology and the exploration potential.
The multicomponent seismic survey was acquired in 2017 and is processed with an innovative workflow using complete wavefield inversion (CWI). This is a processing flow developed by PGS which integrates advanced technology for high-resolution velocity model building and depth imaging using reflections, refractions and multiples. The new high resolution 3D seismic data is revealing geological details never seen before in this area thanks to the acquired broadband data and the state-of-the-art imaging workflow.
Mode conversion noise attenuation, modelling and removal: case studies from Cyprus and Egypt
Author: Jyoti Kumar, Marcus Bell, Mamdouh Salem, Tony Martin, Stuart Fairhead
First Break - 3 December 2018
The authors propose a method to attenuate converted mode energy to improve the imaging for prospective sub-salt targets.
Technology Advances Reveal Unseen Seismic Reflectivity
Author: Andrew Long
Industry Insights - 22 November 2018
The EAGE and the SBGf will host the ‘First EAGE/SBGf Workshop on Least Squares Migration’ in Rio de Janeiro, Brazil, on November 27-28 2018.
Least-Squares Migration (LSM) is an imaging technique that has gained attention in recent years for its ability to improve images obtained by traditional seismic migration methods; minimizing the presence of artifacts, mitigating illumination variations, and increasing spatial resolution. In fact, LSM is the latest step in a continuous path towards revealing the reflectivity information recorded within the full wavefield of any marine seismic dataset.
Latest field trial confirms potential of new seismic method based on continuous source and receiver wavefields
Author: Stian Hegna, Tilman Klüver, Jostein Lima, Endrias Asgedom
First Break - 1 November 2018
The authors describe a new marine seismic method based on emitting and recording of continuous source and receiver wavefields that significantly reduce both sound pressure levels and sound exposure levels.
Côte d’Ivoire: Undiscovered Opportunities and New Data in Open Blocks
Author: Christine Roche
GeoExpro - 29 October 2018
PGS modern broadband seismic coverage of Côte d’Ivoire now provides complete coverage of the area from source to sink.
São Tomé and Príncipe - Four Key Reasons to be Excited
Author: Matthew Tyrrell, Joshua May, Eric Mueller, Orlando Pontes
GeoExpro - 26 October 2018
In recent years, the São Tomé and Príncipe Exclusive Economic Zone (STP-EEZ) has been the subject of significant attention from major oil companies, resulting in applications for exploration licenses and farm-in activities over nine blocks. PGS reprocessed its MultiClient library data using modern processing techniques and conducted a basin analysis study to help understand the recent interest. The study shows that all the elements of a working petroleum system are present in the waters of the STP-EEZ. Continental and transitional crust provide structures and source rocks and PGS basin modelling reveals that these sediments are mature for oil and gas. Long-lived fluvial systems provide quality reservoirs fed from numerous sedimentary catchment areas.