Coil shooting single-vessel full-azimuth (FAZ) acquisition - a technique of acquiring marine seismic data while following a circular path - takes geophysics further by enhancing on current multi- and wide-azimuth (MAZ and WAZ) techniques.
MAZ and WAZ are proven, successful methods of seismic acquisition for complex geological areas. These surveys involve a number of vessels offset from each other, some just towing sources, others towing sources and streamers. The result is better target illumination thanks to greater azimuthal coverage and higher signal-to-noise ratios. MAZ and WAZ have clearly provided important solutions to many complex imaging challenges.
Typically, WAZ surveys are conducted using three or four vessels, each traveling in parallel lines. However, while conducting a project in the Gulf of Mexico, WesternGeco recognized that high-quality full-azimuth recordings could be achieved by acquiring data with a single vessel traveling in a circle, thereby removing the need for the multiple vessels required by today's WAZ designs.
Coil shooting single-vessel full-azimuth acquisition was field tested in the Gulf of Mexico and the Black Sea, and produced positively dramatic results that clearly show the potential for applying the technique on a global scale. Steering the vessel, streamers, and sources in a corkscrew fashion delivers a greater range of azimuths and offsets than parallel WAZ geometries, and there are no non-productive intervals for line changes.
While the concept of circular shooting has been around for years, the application is now available, enabled with the use of Q-Marine technology. Our Q-Fin steering devices accurately control the depth and lateral position of the streamers. A fully braced acoustic positioning network provides accurate positioning information on all the in-sea equipment. Our observation across a number of projects has been that the raw noise levels vary enormously. Single-sensor recording and proven noise attenuation methods handle the full range of this observed crossflow noise without harming signal fidelity.
Coil shooting can address some of the many challenges in imaging beneath salt and basalt, as well as in other complex geological situations.