CGGVeritas’ BroadSeis Improves Interpretation of Marine Seismic Data (France)

In the year since its launch, the BroadSeisTM solution has been deployed in various locations around the world, in different water depths and over different geologies. Building on early 2D results, 3D and elastic inversion data also show significant improvements over conventional data.

CGGVeritas is currently acquiring its fourth commercial proprietary BroadSeis 3D survey in Malaysia as well as a multi-client 3D program in the Central North Sea.

Using BroadSeis, CGGVeritas has demonstrated its ability to emit, record and process ultra-low frequencies in the 2.5-5 Hz range, providing an extra octave of bandwidth over conventional data and enhancing penetration and illumination in sub-salt and sub-basalt environments. In the Gulf of Mexico improvements to the base salt illumination have been achieved. Six octaves of usable data were recorded, providing impressive resolution and texture in the near surface, as well as improved continuity of reflectors at depth. Considerable increases in signal-to-noise ratio and continuity have also been observed sub-basalt on BroadSeis data West of Shetlands. Clear definition of intra and base basalt layers has been seen, including probable multiple basalt flows pinching out.

Off North West Australia the excellent phase control of the extra low-frequency energy provides far better differentiation of layers than conventional seismic. The broad bandwidth provides high-resolution wavelets without side-lobes, which give stunning textural and stratigraphic detail, allowing the interpreter to directly infer lithology and fluid effects in the data. These characteristics have also been particularly noticeable in data from offshore Guyana.

The first 3D BroadSeis survey in Quad 20 of the Central North Sea provided considerable improvements in both lateral and temporal resolution over previous high-quality library data. The BroadSeis 3D data has improved signal-to-noise ratio over the conventional data and the lack of wavelet side-lobes clarifies local impedance contrasts and heterogeneities. Much sharper and clearer fault definition is visible on extracted amplitude maps. The broader frequency content, especially at the low end, improves sedimentary package differentiation and delineation within both the Cretaceous sequence above the BCU (Base Cretaceous Unconformity) and the Jurassic strata below. Initial results from the longer-offset BroadSeis data being acquired in Quad 29 show even greater improvements at these levels, as well as the expected improvements in sub-salt illumination and imaging.

Thanks to the enhanced images that BroadSeis provides, interpreters find it much easier and faster to work with BroadSeis 3D data. The subtlety, texture and continuity within the volume make auto-picking of horizons quicker and more reliable. The higher resolution improves trace-to-trace correlation, allowing horizons to be picked automatically, even through discontinuities, so that the auto-tracking tool can work optimally with little intervention. The absence of side-lobe interference allows the interpreter to pick reflectors corresponding to geological layers with greater confidence.

The BroadSeis deghosting algorithm is true-amplitude and angle stacks over a known AVO anomaly showed comparable but clearer AVO effects to those from conventional data. The improved low frequencies achieved using BroadSeis allow more stable and accurate prestack inversion, delivering more quantitative and reliable P-wave impedance attributes.

The many examples of BroadSeis data that CGGVeritas has acquired from around the world all show considerable improvement in data quality, increasing both lateral and temporal resolution. Having successfully removed the receiver ghost, the company’s researchers are now working on further improvements to the technique by removing the source ghost as well – early results show that data from 2-200 Hz can now be recorded, the upper limit being imposed only by the anti-aliasing filters of the 2 ms recording used in the trial.

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Source: CGGVeritas, September 19, 2011;