Wide-tow triple source solutions were employed to resolve targets from shallow to deep for MAZ surveys in the Viking Graben in 2019 and 2020.
The 2019 GeoStreamer X multi-azimuth survey (MAZ) was acquired in the Viking Graben, offshore Norway, and comprised both long streamer tails for full waveform inversion (FWI) based velocity model building (using refracted waves), as well as wide-tow triple source to enable both optimal near offset coverage and improved acquisition turnaround. The source separation for the triple source was 2 x 112.5 m, i.e., 225 m total separation. In 2019, this was the widest source separation ever towed from a single streamer vessel.
Ramform Vanguard returned to the Viking Graben in 2020 and extended the multi-client MAZ program. For the extension program, the triple source separation was 2 x 125 m, resulting in 250 m total separation throughout the survey. The vessel improved her own source-tow record and acquired high-quality multi-azimuth data in an innovative and cost-effective manner. Imaging results from these surveys are already available, and demonstrate the effectiveness and value generation of modern acquisition solutions.
The figure below illustrates the results of the 2019 setup, with significant uplifts in near-surface illumination from the wide-tow solution compared to a standard narrow-tow configuration. The wide tow image exhibits a number of small-scale features which could not be recovered by data interpolation with the legacy dataset.
Comparison of time slices at ca.200 ms two-way traveltime and (inset) shallow seismic cross sections. The example that shows significant footprints and illumination gaps (left) was acquired with a standard dual source and a 10 x 75 m streamer spread in 2011. The wide-tow triple source configuration used in the same area in 2019 enabled seamless shallow imaging and higher efficiency. The orange arrows indicate the respective positions of the slices and the cross-sections.
The multi-azimuth program continued with a set-up providing even higher acquisition efficiency in 2020. As illustrated in the figure below, imaging of the water bottom and very shallow overburden reveals several structural details as well as possible shallow gas. Although good near offset coverage may be expected from a single survey direction acquired with wide-tow sources, using all the azimuths in processing proves to be robust, and produces an image practically free of acquisition footprint. The data are processed and migrated at a 2 ms sampling interval and output on a 6.25 m x 6.25 m grid. Although this area has no prospectivity in the upper several hundred meters, the information is essential for future field development, as shallow hazard identification is a prerequisite prior to drilling operations. In addition, interpreters benefit from a full 3D image as opposed to 2D site survey investigations, thus saving time, money and providing more reliable attributes.
High-resolution shallow images generated from a multi-azimuth program in 2020 using wide-tow triple sources. The imaging bin size is 6.25 m x 6.25 m. The dashed yellow line (top left section) indicates the position of the time slice. The image is free of distortions related to missing near offset information, which are often found in standard dual-source data.