oa Geophysical Benefits and Operational Characteristics of Steerable Marine Seismic Streamers

Multi-streamer marine acquisition is possibly the most successful application of 3D seismic. However, the method has problems and short-comings. Cables are influenced by tides and currents, and precise control of streamers is not possible. In order to prevent tangling the streamer separations are high, so that the high-fold acquisition is difficult to achieve. Streamers are affected by the dynamics of the towing vessel, leading to phenomena such as 'fantailing'. Time-lapse surveying is now commonplace, to monitor production-induced changes in the reservoir. 4D effects are subtle, so it is essential to remove sources of error that could mask the actual differences. Repeatability is a measure of how well the original survey has been emulated by the monitor surveys, by replicating source and receiver positions. This is difficult with existing technologies. The solution is to control the lateral behaviour of the streamers. Vertical control of seismic cable positions is achieved using 'birds'. This concept can be used to control horizontal motion, i.e. employing a a vertically mounted fin. This enhances streamer control so that cable separations can be reduced, enabling higher density acquisition. Results will be shown based on modelled data and case studies.