Coil Shooting is a technique developed to acquire a full azimuth dataset with a single vessel towed streamer operation. The first full 3D Coil Shooting survey was conducted offshore Indonesia over the Tulip field in August and September 2008. Two proof-of-concept “coil feasibility” studies had already been carried out in GOM, and the Black Sea. However, as the first full production 3D Coil project, the acquisition still presented some challenges to the planning and execution of the survey. This paper presents the acquisition review of the Tulip Coil survey, focusing primarily on the acquisition planning, deployment, QC phases and production efficiency of the project with special focus on the importance of adjusting the straight line mindset of marine streamer geophysicist.
Towed streamer marine seismic acquisition generates a dataset with a limited azimuth range, of the order of 10 degrees. In areas of complex geology, this limited azimuth collection, can result in very poor illumination of the reservoir by the seismic wave-field, due to bending and scattering of the ray-paths in the over-burden. Over the last five years, efforts to mitigate this poor illumination effect, with marine towed streamer surveys, have focused on acquisition solutions to generate seismic datasets with better azimuth distribution. These efforts have included multi-directional and multi-vessel geometries to acquire surveys rich in azimuth. These techniques have proven to provide significant value in complex imaging environments; however they can be constrained by the cost and availability of the multi-pass, multi-vessel operations.
Coil Shooting is an acquisition technique where the vessel follows a circular pre-plot line. More circles are repeated in the X and Y directions to build up fold, offset and azimuth distribution. This method allows for full azimuth (FAZ) acquisition using a single vessel, shooting on a continuous turn. Line changes are short, of the order of minutes, resulting in high acquisition uptime and efficiency. The offset and azimuth distribution of Coil Shooting is excellent; as good as and sometimes better than any of the wide, multi azimuths (WAZ/MAZ) techniques.
The first production deployment of the Coil Shooting technique was conducted over the Tulip field in the Bukat block offshore Indonesia (Fig 1). The final acquisition parameters were chosen following collaborative and intensive survey designs efforts. This included modeling and comparison of the coil size, location, density and quantity, as well as tow depths and streamer spread configuration. A vessel with the capability to steer the streamers, acquire fine spatial sampling for noise attenuation and record accurate receiver position was required and selected and acquisition planning and deployment commenced.
The full 3D survey was acquired in August and September 2008. The survey was designed in a way that it consisted of rows and columns of coils on the pre-plot plan. The shooting strategy was planned such that moving between coils and between rows of coils included flexibility to acquire the coils in both clockwise and counter-clockwise direction. Pre-plot illumination modeling suggested the coverage would be independent of the coil acquisition direction.