Blended acquisition & iterative deblending
Learning objectives
- State the blended-acquisition productivity gain (2-4×)
- Describe the iterative fit-subtract-refit deblending loop
- Quote required jitter (±60-200 ms) and why under-jitter fails
- Link OBN recording to simultaneous-source tolerance
Blended (simultaneous-source) acquisition has two or more sources firing within seconds of each other. Every receiver records the sum. Deblending separates the superposed shot records in processing. Classical single-source shooting holds 6-10 s between shots; blended cuts that to 2-4 s per shot pair, with ±100-200 ms random jitter.
Why jitter is the trick
Sort the blended record into shot-1’s time frame. Shot-1 events align coherently across traces; shot-2 events appear at the jittered offsets, which DIFFER per shot, so they scatter as trace-to-trace outliers. A coherence filter (f-x median, curvelet soft-threshold) extracts shot-1; subtract it from the blended record to get a shot-2-dominated residual. Sort into shot-2’s frame, filter, subtract, iterate. Three to five iterations typically converge.
Productivity gain
Two blended sources ≈ 2× shots/day. Three vessels ≈ 2.8×, four vessels ≈ 3.4×, diminishing returns because de-blend cross-talk rises with source count. Marine streamer sweet spot: 2 vessels. OBN projects routinely push 4-6 source vessels because nodes record continuously regardless of source cadence, and the coherence filters can separate many overlapped shots. Some ultra-simultaneous-source (USS) programmes have shot 10+ sources in parallel.
Jitter requirements
Below ±60 ms the jittered shot-2 events start to look coherent in shot-1 frame, and de-blending leaks. ±100-200 ms is industry standard. Above ±300 ms the inter-shot gap must widen to accommodate, eating into productivity. For OBN the jitter can go to a full second because the nodes continue recording regardless.
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.