Deepwater Ocean Currents West of Britain: Measurements & Criteria Development

Abstract

Tranche-6 in the Faeroe-Shetland Channel is a deepwater site characterised by complex currents of potentially high magnitude. Preparation for drilling at Tranche-6 included development of extreme and operational environmental criteria. Wind and wave conditions could be estimated with adequate accuracy from existing hindcast studies. Information on ocean currents is in general lacking, and hindcast modelling for currents is not nearly as accurate as for waves. Measurement programs collected data near the site in June-November 1992 and April-September 1995. Recorded data confirm strong currents varying in direction with depth. The data are the basis for preliminary extreme criteria and generic current profiles used in operability studies. Realtime current measurements were also made during Tranche-6 drilling, which began in May 1998, to support station keeping and riser management decisions. A weakness in advisory capabilities exists due to the lack of reliable current forecasts.