The paper discusses the development of a new metocean design basis for a deep water harsh environment off the NW shelf of Europe. The principal steps taken to achieve this, in an auditable and scientific manner, within the constraints of the available data and short time scale, are described. The industry partnership approach adopted to ensure early acceptance by all the relevant contributors, is outlined.
This paper discusses the development of a new meteorological and oceanographic ("metocean") design basis for the first West of Shetland (WOS) Developmentsquadrant 204 (see Fig. 1). This area is exposed to the fill force of Atlantic storms which together with the water depth and a complex ocean current regime, presentunique challenges.
In the general are the sea bed slopes from the edge of the continental shelf (approx, 200 m), to the bottom of the Fame-Shetland channel, where depths are 1000 m or re. The development location is in a water depth range of 375 m to 850 w with the first field "Foinaven", in 450to 500 m. For comparison the deepest North Sea development in the UK sector is BP's Magnus, in 185 m. ig. 2 demonstrates the differences in metocean designcriteria and illustrates the scale of the engineering challenge.
In the early 1970's, weather ships sponsored by the UK Offshore Operators Association (UKOOA) at "Fitzroy" (60°W, 4°W) measured wind and wave data. These were replaced later in the 70's by weather buoys at the "Foula"location approx. 50 km to the ENE. In the 1980's, dataas collected by the UKOOA data buoy DB3 in Block 206/6. During summer exploratory drilling, oceancurrent measurement campaigns by individual operators are also supported the drilling programmed in the area.
In addition to the measured wind and wave data the North European Storm Study (NESS) provides data from computer models (ref. 1). The NESS dataset contains some 25 years of winter data from 1964 to 1989, and provides output at 30 km intervals over the whole WOS area). Selected grid points and other data source locations are in Fig. 1.
Early metocean criteria for Foinaven issued in late 1993, were based on proprietary work carried out for the North West Approaches Group (NWAG) in 1988. NWAG is an ongoing joint industry group, with the objective of exchanging and collecting metocean data for the WOS area. It was formed in 1986 and currently has 13 oil company members (chaired by BP), together with the UKHealth and Safety Executive (HSE).
To reduce the period from discovery to development ("fast-track" project), requires considerable compression of the concept engineering, with design basis development in parallel with reservoir evaluation. The metocean design basis was, therefore, required considerably earlierthan has been traditional practice. A decision on the metoman data gathering was made in late 1993 afterconcept engineering identified the faibility of a floating production development on Foinaven.