Illumination Analysis from Coil Survey Design and Acquisition to Coil Processing Solution

A narrow azimuth survey and an overlapping Coil survey were acquired and processed for TOTAL offshore Angola. After fast track processing, a direct comparison showed that at a specific location a sub-salt steeply dipping event was better defined on narrow azimuth image than on the Coil image. This case study illustrates how illumination analysis can be used to make critical survey design, acquisition and processing decisions. The initial flower plot analysis helps determine the survey design requirements to illuminate target horizons, and will fully justify the need for a full azimuth design. Then, an acquisition illumination analysis complements the previous analysis by creating offset and azimuth illumination maps for chosen design. This identifies illumination and shadow zones on the target horizon. This can be directly related to the seismic data and used to design an appropriate processing solution. Finally, during the processing phase, the specific azimuth contributions identified from illumination analysis need to be separated into azimuthal images. These are intelligently stacked to create the final image, using an intelligent stacking method, designed to retain azimuth specific contribution. To use the full benefit of Coil Acquisition, this two-steps processing strategy derived from the illumination analysis, is essential.