GeoStreamer X Could Redefine Multi-Azimuth Seismic Acquisition in Brazil
This feature article outlines how the innovative GeoStreamer X method can be applied in Brazil. It would improve spatial sampling and add complementary azimuths from new multisensor broadband acquisition to enrich existing seismic data. The full article was published in Hart Energy online, May 2020.
Illumination issues are addressed with GeoStreamer X using a seismic survey design adapted to the local geological challenges, along with towed-streamer efficiency that guarantees timely delivery of results. Multisensor recordings enable advanced processing to achieve significant improvement of existing data. These recordings are provided by multiple sources for improved spatial sampling and efficiency; wide-tow sources (if needed) for optimal near-offset coverage and amplitude with variation offset (AVO); longer offsets for reliable velocity model building; and cost-effective multi-azimuth (MAZ) illumination. This results in rapid turnaround from acquisition to the final image.
Read the full article in the May edition of Hart Energy 'Redefining Multi-Azimuth Seismic Acquisition'.
Solving Imaging Challenges in Brazil
There are many factors that make survey design in Brazil challenging. Large structures of salt combined with deep sediment basins and volcanic rocks set the background for very deep reservoirs and represent very challenging geology to image. Meanwhile, environmental regulations constrain the operational parameters for seismic acquisition. This combination of geological and operational challenges is best addressed by a well-managed holistic approach for the entire process covering planning and geophysical modeling, operations in the field, and advanced processing and imaging.
PGS has a large footprint of MultiClient data and extensive operational experience in Brazil. This provides many opportunities to design and deploy GeoStreamer X acquisition configurations that best meet the complex imaging challenges in Brazil. Building a large-scale model that incorporates realistic details from a number of different major discoveries makes it possible to test varous acquisition configurations. They can be evaluated to see which configuration best addresses the geological, geophysical, and operational challenges.
With advances in full-waveform inversion (FWI) earth-model building workflows, making sure the acquisition configuration provides the best data possible for FWI has become a critical step in survey design. Confidence in the velocity model building process can be increased by adding refracted energy. The PGS FWI method uses diving waves, refractions, and reflections to deliver deep velocity model updates in a stable manner without relying on very long offsets.
The example shown above is based on a cross-section, representing the geology of the Carcará discovery. It was used to determine the offsets required to achieve velocity updates using refracted energy in FWI. With both reflected energy and diving waves, it becomes possible to increase the bandwidth for FWI to higher frequencies, achieving unprecedented resolution at the level of presalt reservoirs.
The model derived from real data for FWI feasibility studies demonstrates that diving wave velocity updates will reach the Santos Basin presalt with offsets less than 20 km, well within the operational range of modern streamer acquisition configurations.
A GeoStreamer X design for Brazil needs to deliver sufficient offsets for presalt FWI while meeting regulatory requirements. Advanced modeling of synthetic data in the complex geology in Brazil shows that it is possible to achieve the required offsets using towed-streamer seismic. Several streamer geometries have been identified that record long offsets with minimal environmental footprint. The most efficient solution is a standard long-offset configuration from a single vessel towing a tailored source. Alternatively, highly effective configurations can provide even longer offsets, such as simultaneously acquired, sparse-source long offsets where additional sources and additional receivers may be towed by a separate vessel. In all cases, combining these streamer geometries in a MAZ survey to improve illumination is expected to provide excellent images of presalt targets.
By using existing data and experience, surveys can be designed to enhance existing datasets and get the best images and information in a wide variety of geological settings while complying with local regulations.