Over/Under Wavefield Separation

Extending bandwidth and improving signal-to-noise

The benefits of acquiring and processing Over/Under data are clear; the recorded bandwidth is extended at both low and high ends of the spectrum, while the ability to tow streamers at greater depths, and hence, in a quieter environment improves the signal-to-noise ratio. The result is a cable-deghosted dataset with improved structural imaging, inversion, and rock property characterization.

WesternGeco now offers a full source and receiver over/under solution for optimal wavefield separation.

Over/under processing uses wavefield separation techniques to combine data from the over and under cables. The WesternGeco approach is based on the Posthumus method (Posthumus, 1993) to estimate local wave height and water velocity, then performs decomposition of the up- and downgoing wavefields to combine datasets.

Although the principles of Over/Under combination have been understood for some time, effective acquisition and processing relies on the ability to tow streamer pairs (one on top of the other) with a high degree of control and accuracy. Q-Marine acquisition is the enabler to this process.

Over/under regularisation
Matching Over/Under inline positions

When over/under cables are towed, there is often a different amount of stretch in the under cable compared to the over cable. This causes introduction of errors when the over/under combination processing is applied.

Over/under regularization allows the over/under cables to be realigned such that their inline positions match and errors are removed.

• Sonneland, L., Berg, L. E., Eidsvig, P., Haugen, A., Fotland, B. and Vestby, J., 1986, 2-D deghosting using vertical receiver arrays, 56th Ann. Internat. Mtg.: Soc. of Expl. Geophys., Session:S11.6
• Posthumus, B. J., 1993, Deghosting using a twin streamer configuration: Geophys. Prosp., Eur. Assn. Geosci. Eng., 41, 267-286

• A Marine Broadband Case Study Offshore China (EAGE 2010)
• Unbiased deterministic seismic inversion: more seismic, less model (First Break November 2009)
• Adding streamers to an over/under configuration can improve imaging (World Oil September 2008)
• Optimized deghosting of over/under towed-streamer data in the presence of noise (The Leading Edge February 2008)
• Over/under towed-streamer acquisition: A method to extend seismic bandwidth to both higher and lower frequencies (The Leading Edge January 2007)
• Over/under acquisition and data processing: the next quantum leap in seismic technology? (First Break June 2006)
• Imaging beneath basalt using an over/under towed-streamer configuration (World Oil May 2006)