Transitioning from Towed Streamer to Ocean Bottom Seismic - a Mixed Acquisition 4D Benchmark

The Kinnoull field in the North Sea has both narrow azimuth towed streamer (NATS) and OBC surveys acquired pre-production. When an OBN monitor was acquired, this allowed us to directly compare the optimum OBN-on-OBC 4D to an OBN-on-streamer, or ‘mixed acquisition’ 4D.

NRMS of the benchmark OBN-on-OBC result was 0.18. To understand the impact of the rich azimuth coverage of OBC data, a decimation trial was carried out, limiting the OBN-on-OBC processing to narrow azimuths similar to the NATS survey. The resulting 4D difference was interpretable, but had elevated noise levels, with NRMS of 0.38.

Comparing this narrow azimuth OBC result to 4D using the NATS baseline gives us the impact of the acquisition system, particularly the receiver datum. While there were some similarities in the location of hardening signals, the NATS 4D was too noisy to reliably interpret, with NRMS of 0.58. It is thought that one of the main causes of this may be non-repeatable peg-leg multiples.

We conclude that for Kinnoull, and similar North Sea fields, OBN-on-NATS 4D is not currently possible, so to successfully transition from towed streamer to ocean bottom seismic 4D will require a transition vintage where both types of data are acquired simultaneously