A 4D Seismic Processing Case Study in a Difficult Shallow Offshore Complex Carbonate Field.

Time-lapse seismic processing in carbonate fields having complex geology and in difficult seismic contexts requires highly specialized teams for success. Our field case has a flat structure, a poorly-imaged but highly reflective sea bottom and is covered by towed-streamer data in about 60m of water depth. Multiples contamination is severe and these are coherent with primaries. We tested several 4D seismic processing routes using a base and two monitor surveys and have summed up our experiences in four learning points: A simplified targeted demultiple flow avoiding adaptive methods improves 4D metrics better than a complicated one. A guided co-denoise technique using base and monitor vintages attenuate non-repeated noise from data while preserving 4D timeshifts and 4D amplitude changes. A mute design optimization prior to stack attenuates residual multiples that degrade 4D signal. Finally, seismic acquisition parameters have a strong impact on computed 4D seismic attributes even if this may not be the case in 3D. These learning points coupled with multidisciplinary interactions and an iterative processing QC strategy assure the delivery of data with a more interpretable 4D signal that permit the delineation of depleted zones, flushed zones and by-passed oil for future infill-well drilling and optimal reservoir management.