Ocean Bottom Nodes (OBN) Processing Case History: Dalia 3D Survey, Offshore Angola

In 2008 and 2009, Ocean Bottom Nodes (OBN) have been used by Total to acquire an industrial scale seismic survey on the Dalia oilfield in deep offshore Angola, and compare it to conventional undershoot as an alternative technology to overcome field obstruction issues and related HSE risks that occur in such production environments. This acquisition was part of a time lapse survey program involving baseline and monitor towed streamer acquisitions. This acquired OBN monitor data has a significant overlap with its streamer equivalent monitor, and can easily be compared to conventional acquisition and processing. Processing OBN data was a challenging task requiring quick learning and was based on several objectives: 1- repositioning; 2- to correct time shifts from tide, synchronization or clock drift; 3- to reduce differences between OBN and towed streamers; 4- to preserve the bandwidth; 5- to match the OBN data to the streamer data. The processing team strongly benefited from the framework of the R&D collaboration in place between CGGVeritas and Total. Numerous innovations were quickly transferred to the operation, to be used or tested for future surveys. Finally, when compared, OBN data and towed streamer data give close results and a relevant 4D response.