In this case study we present the results from time-lapse analysis on a Wide Azimuth Towed Streamer (WATS) data set from 2010 that was compared to a pre-production Narrow Azimuth Towed Streamer (NATS) data set from 2002 at King / Horn Mountain (KHM) Fields in the Gulf of Mexico. The WATS data set was acquired to improve the overall imaging of the fields and was not acquired for the goal of time-lapse. Nevertheless, we were able to extract a clear time-lapse signal from the WATS survey. The cost of extracting this time-lapse signal was highly reduced compared to a conventional dedicated time-lapse streamer survey acquisition as it only required reprocessing.
Combined processing of these datasets was a technological challenge. The two datasets were co-binned onto a common grid and a common narrow azimuth dataset was extracted. This dataset was analyzed and interpreted and a clear time-lapse signal was observed in the extra-salt areas. The observations in the time-lapse signal were similar to the previously acquired dedicated time-lapse survey from 2005. The noise level from the WATS on NATS time-lapse was higher than from the conventional dedicated time-lapse survey, but the signal was strong enough to be observable above background noise. Observations from this time-lapse project allow us to better understand the production history of the field, lower the risk on some of the infill targets and avoid drilling wells into potential gas caps that may have formed in the fields. The results from this study demonstrate that usable time-lapse observations can be extracted from combining WATS and NATS data at a much reduced cost.