Simultaneous shooting in marine

Part 4 — Marine acquisition

Learning objectives

Define blended marine acquisition: overlapping shot records separable in processing
Quote typical speedup (2–4×) and required jitter (± 60–200 ms)
Explain why OBN makes blending easier than streamers do
Recognise deblending as an iterative median / sparsity-based separation

Classical marine shooting waits 6–10 s between consecutive shots so the last shot’s returns fully decay. Simultaneous (blended) shooting overlaps the shots — a second vessel fires 2–4 s after the first, and the recordings sum on every receiver.

Why it works

If the second shot’s time is jittered randomly per shot (typically ± 100–200 ms), it looks like incoherent noise when you sort the data by the first shot’s time. Iterative deblending separates the two: estimate shot 1 from the record (suppressing shot 2 as noise), subtract it, what remains is shot 2 + true noise. Repeat until both estimates stop changing.

Productivity gain

Classical single-vessel: ~500 shots/hour. Two-vessel blended with 3 s gap: ~2,400 shots/hour — nearly 5×. Three vessels: ~7×. Four vessels: 10× but with increasing deblending cross-talk. The sweet spot for streamer work is 2–3 vessels; OBN projects routinely go to 4–6 source vessels because the nodes record continuously regardless of source timing.

Jitter requirements

Too little jitter and shot 2 looks like coherent shot-1 noise — deblending leaks. Too much jitter and the inter-shot gap needs to widen to accommodate it, losing productivity. Industry sweet spot: ± 100–150 ms random per shot. Below ± 60 ms, deblending typically fails in the wavelet envelope of the primary.

OBN’s advantage

On a streamer, the receivers are live only while the survey is running; inter-shot gap sets the shooting cadence directly. OBN records continuously — a source vessel can fire any time without waiting for another vessel’s tail. This is why OBN has pushed marine shooting to truly independent simultaneous source (ISS) geometries where multiple vessels fire at essentially uncorrelated times.

References

Beasley, C. J., Chambers, R. E., Jiang, Z. (1998). A new look at simultaneous sources. SEG Annual Meeting Expanded Abstracts, 133–135.
Berkhout, A. J. (2008). Changing the mindset in seismic data acquisition. The Leading Edge, 27(7), 924–938.
Mahdad, A., Doulgeris, P., Blacquière, G. (2011). Separation of blended data by iterative estimation and subtraction of blending interference noise. Geophysics, 76(3), Q9–Q17.
Berg, E., Svenning, B., Martin, J. (2010). OBN technology — recent developments. EAGE Workshop on Permanent Reservoir Monitoring.