First full-azimuth towed-streamer survey offshore Brazil - An acquisition and survey design case study

I n geologically complex areas, the limited azimuth range associated with single-vessel straight-line acquisition can result in the target reservoir being poorly and/or randomly illuminated by the deployed surface spread. While the source wavefront propagates in all directions, only a small proportion of the reflected wavefront is captured by the surface receiver spread. Driven primarily by the need to improve subsalt illumination in the Gulf of Mexico, the industry experimented with a number of multivessel geometries; most recently, coil shooting has been deployed over a number of complex geologies worldwide. The first coil shooting survey offshore Brazil was recently acquired with the goal of improving the imaging of the pre-salt target reservoirs for an exploration project. Coil shooting is a technique in which a single towed-streamer vessel shoots a circular “line”. This circular line is repeated inline and crossline to build up fold, offset, and azimuth distribution. This paper will present the survey design process and results, and additionally, present some of the challenges involved in planning and acquiring this unique geometry.