Source and streamer towing strategies for improved efficiency, spatial sampling and near offset coverage
Several towing concepts have arisen in recent years that break the convention of towing two source arrays between the innermost two streamers in a multi-streamer 3D configuration (‘dualsource shooting’). Three ‘arrays’ of one or more sub-arrays were towed more than 20 years ago to improve cross-line spatial sampling, but inline spatial sampling and fold were compromised by inefficient recycling times on air gun compressors and limited recording lengths. Modern acquisition systems enable continuous recording, very short physical shot intervals, and up to six source arrays being deployed between the innermost two streamers; always with the ambition of improving cross-line spatial sampling. I discuss two newer variations to these scenarios using either dual-source or triple-source shooting, although the principles may be expanded to more sources distributed in the cross-line direction: 1. Towing source arrays outside the innermost two streamers such that survey efficiency is improved courtesy of the nominal sail-line separation being increased. It is demonstrated that cross-line fold becomes irregular as source separation increases in the cross-line direction, so complementary processing methods may be required to reduce imaging artifacts. 2. Alternatively, if the sail-line separation is based on a conventional source towing scenario, some flexibility may be created in terms of near offset sampling.