Marine towed streamer seismic using continuous line acquisition

Abstract

The most cost-effective way to acquire 3D seismic data offshore is by towed-streamer survey; the majority of these surveys are acquired using a vessel shooting a series of parallel straight lines to cover the survey area. When each line is completed, the vessel turns and starts the next line until the survey area is covered. Normally, data are not acquired during the turns due to difficulty in maintaining streamer lateral separation and the extra noise generated in the data. This means that, depending on the survey size and shape, there may be significant non-production time. Advances in marine acquisition technology have made it possible to acquire usable data as the vessel turns, which increases productivity because there is little or no non-productive time associated with line changes. Streamer steering systems allow spread shape to be maintained during line changes, and new streamer designs and processing schemes mean that noise no longer presents a barrier to utilising these data. We present some background on this technique and discuss a recent survey in New Zealand. In this survey, the straight line sections were shortened and turn data were incorporated into the survey. This enabled data to be acquired in shallow water areas. In addition, the data were acquired using a fan shooting technique to improve coverage and a variable depth cable with a multilevel source to produce ghost-free data, and therefore extend the data bandwidth. These three streamer configurations were combined to efficiently acquire broadband data in a challenging area.