4D Acquisition and Processing of streamer and OBC data in West Africa: A case history to demonstrate how survey planning and advanced processing techniques improve repeatability for reservoir monitoring

Summary The feasibility analysis, survey planning, seismic acquisition and time-lapsed processing of a West Africa 4D seismic dataset over the producing Elon Field Area of the Okume Complex, Equatorial Guinea is presented. The survey planning and execution occurred in 2011-2012. Prior to the expenditure of significant funds required for the execution of an ocean bottom cable (OBC) acquisition, several steps were taken to determine the magnitude of the detectable 4D change for this reservoir and to define the optimal design parameters to match the planned OBC Monitor survey the existing Marine Streamer Baseline dataset. In areas where field production infrastructure exists, seismic operations pose significant challenges from the standpoint of safety, as well as for obtaining adequate coverage (in fold, azimuthal coverage and offsets) in key areas near field infrastructure. Differences in source/receiver types, noise levels, and geometry require processing to utilize advanced techniques including deghosting, model-based multiple removal, adaptive noise attenuation and 4D co-binning. The streamer (baseline) and the OBC (monitor) are compared after PSDM and gather conditioning for repeatability using NRMS and time-shift analysis presented. The OBC dataset was also processed independently utilizing the split-spread and wide azimuth component that was removed during the 4D binning process in order to gauge the level of improvement due to the increase in fold and subsequent trace density.