DISCover—Deep Interpolated Streamer Coverage

Increased Low Frequencies for Deep Penetration and High Frequencies for Improved Resolution

DISCover deep interpolated streamer coverage, is designed to efficiently deliver 3D seismic data with an enhanced bandwidth, providing increases in both low frequencies for deeper penetration and high frequencies for improved resolution. The method, enabled by the Q-Marine seismic system, simultaneously acquires data from several shallow-towed streamers, designed to optimize mid- to high frequencies, with data from a smaller number of deeper towed streamers, providing low frequencies. These data are combined in processing to optimize signal-to-noise (S/N) ratio over the entire bandwidth. Potential applications include improved imaging beneath highly absorptive overburdens such as basalt and salt, or acquiring data suitable for inversion to absolute rock properties. Data acquired in this way are also more robust to poor weather conditions than conventionally acquired data.

Conventional towed-streamer systems deploy sources and streamers at shallow depths, typically between 6 and 10 m. This configuration enables recording of the high frequencies needed for resolution, but attenuates the low frequencies needed for stratigraphic and structural inversion. Shallow towing also make the data more susceptible to environmental noise such as waves, swell and wind. Towing sources and streamers at deeper depths enhances the low-frequency content of the data and can increase the signal-to-ambient-noise ratio; however, it attenuates the high frequencies.

Designing tow-depths for conventional towed-streamer surveys therefore requires a compromise to optimize bandwidth and S/N for a specific target depth or two-way traveltime, often at the expense of other shallower or deeper objectives. Data recorded by streamers towed at different depths can avoid this compromise, delivering the high-frequency characteristics of conventional shallow-towed configurations and at the same time the low-frequency characteristics of deep-towed data. Further enhancements to data quality can be derived from deploying a multi-layered source array.

WesternGeco Q-Marine technology has delivered the accuracy needed to enable the benefits of DISCover to be realized. Q-Marine streamers can be steered with the required horizontal alignment and accurate depth control.

The Importance of Low Frequencies

As seismic data processing, imaging, and inversion techniques evolve, the presence of low frequencies in the recorded data has become increasingly important. Low frequencies have always been crucial for the imaging of complex structures in areas of highly absorptive media. However, new methods for developing velocity models, such as full waveform inversion and other inversion techniques for deriving rock properties from seismic data, require the presence of low frequencies in the data below that achievable from shallow towed streamers alone.

Using the DISCover Technique in India

In India, WesternGeco has successfully deployed the DISCover technique to deliver broadband seismic data. Results show seismic data rich in both high and low frequencies. Prestack time migration and prestack depth migration processing were carried out in the WesternGeco GeoSolutions Center in Mumbai using advanced workflows. These have shown a substantial improvement in bandwidth compared to legacy data, specifically in sub-basalt areas.

DISCover is offered today from any of the Q-Marine enabled vessels in the WesternGeco fleet.