Capstone, Gulf of Mexico deep-water WAZ

Part 10, Real-field capstones

Learning objectives

Describe multi-vessel WAZ geometry (streamer vessel + 2-4 source vessels)
Quote typical numbers: 10-15 streamers, 8 km streamer length, ±3-4 km offset
Link aspect ratio to sub-salt imaging capability
Recognise Thunder Horse (2004) as the first major WAZ campaign

Deep-water sub-salt imaging in the Gulf of Mexico sits at the intersection of two hard constraints: targets are 5-7 km below mudline, and salt canopies bend surface-seismic energy around the target rather than into it. BP’s 2004 Thunder Horse campaign pioneered multi-vessel WAZ shooting as a solution.

The geometry

One streamer vessel tows 10-15 parallel streamers, each 8-10 km long at 75-150 m crossline spacing. Two to four additional SOURCE vessels hold station at ±3-4 km lateral offsets from the streamer sail line, firing in rotation. Every shot from every source vessel illuminates every streamer receiver, but from a different angle. Aspect ratio (crossline / inline offset spread) climbs from NAZ’s 0.15 to ≈0.5 for 3-vessel and ≈0.7 for 4-vessel WAZ.

Economics

Streamer vessel day-rate ≈ $500k; each source vessel ≈$ 300k. A 3-source-vessel WAZ is therefore $1.4M/day, times 100-140 days for a typical programme =$ 150M- $200M total including crew, fuel, insurance, re-shoots. That’s 2-3× a classical single-streamer NAZ survey over the same area, but sub-salt images that de-risk$ 300M development wells more than pay back.

Field results

Thunder Horse WAZ (BP, 2004) doubled the estimated reservoir volume after re-imaging; Atlantis and Mad Dog followed the same playbook. WAZ is now standard practice in Gulf of Mexico deep-water, West Africa, Brazil pre-salt, and offshore Malaysia. The primary evolution in the past decade: source-vessel count trends from 2 → 4, and streamer counts from 10 → 15-20.

References

Vermeer, G. J. O. (2002). 3-D Seismic Survey Design. SEG Geophysical References 12.
Cordsen, A., Galbraith, M., Peirce, J. (2000). Planning Land 3-D Seismic Surveys. SEG Geophysical Developments 9.
Tenghamn, R., Brown, J. (2000). A new dual-sensor towed-streamer technology. SEG Annual Meeting Expanded Abstracts, 1-4.
Soubaras, R., Whiting, P. (2011). Variable depth streamer, the new generation. CSEG Recorder, 36(2), 27-31.