The US unit of Royal Dutch Shell PLC let a contract to Multiwave Geophysical Co. ASA, Bergen, Norway, to overshoot previous seismic lines across 13 unspecified Shell and partner fields in the US Gulf of Mexico.
Acquisition started in July for 5 weeks using the Polar Venturer vessel and a supply vessel rigged with a streamer to acquire 2D data using the same technique as a test survey carried out over 2 fields in the fourth quarter of 2004.
Using a vessel to tow a short 2,000 m streamer, the test survey involved shooting over the location of an existing 3D data line on three occasions. Each subsequent pass increased the distance between the source and the front of the streamer in order to acquire data with 6,000 m offsets. The first pass collected 0-2,000 m offset data, the second pass collected 2,000-4,000 m offsets, and the third pass collected 4,000-6,000 m offsets.
Shell brought this acquisition method to Multiwave’s attention to obtain closely repeated shot and receiver positions. Shell anticipates employing the method in 3D for full-field 4D seismic surveys. ✦
