Strathspey vertical-cable seismic survey: a North Sea first

Abstract

In 1995–96, the Strathspey Field Group (Texaco, Shell Esso, and Oryx) acquired and processed the first vertical-cable seismic survey in the North Sea. Strathspey is a tilled, eroded fault block, and production is from the Brent and Statfjord reservoirs. The eastern flank of Strathspey is marked by low-angle foolwall degradation complexes in both reservoirs. Historically, these features have been very difficult to image seismically, both on Strathspey and on neighbouring fields. Vertical-cable seismic, with its uniform distribution of azimuths and its economical 3D pre-stack depth migration, was judged to have the best potential to image these features. The survey was acquired in six swaths in the summers of 1995 and 1996. Processing of the pre-stack depth-migrated data volume was completed in October of 1996. The dataset shows remarkable improvement over the previous 3D dataset (vintage 1985). and compares favourably with the Brent Field dataset which was acquired immediately to the north of Strathspey in 1995. Improved data quality has allowed a more confident interpretation of the low-angle fault scarp features, as well as a more detailed structural model of both reservoirs, In addition, the superior data resulted in an improved assessment of the remaining exploration potential in the Strathspey area. The information gained from the interpretation of the vertical-cable seismic data has given the field partners more confidence in siting wells and in the reservoir simulation models.