Auk to Kittiwake: 15 Years' Progress in North Sea Jacket Engineering

ABSTRACT The Kittiwake oil field has been developed using the first of a new generation of liftable slimline jackets to be installed in the North Sea by Shell UK Exploration and Production, known as Shell Expro, operator in the UK sector the North Sea on behalf of Shell and coventurer Esso Expro. Production began in September 1990 - almost exactly 15 years after Shell Expro began production from Auk, its first North Sea oil field. This paper considers the progress of jacket engineering over these 15 years by comparing two jackets supporting topsides facilities which perform comparable functions in very similar conditions. INTRODUCTION The Kittiwake platform is a self contained drilling, production and accommodation platform located in 85 metres of water approximately 100 miles east of Aberdeen in the Central North Sea sector of the UK Continental Shelf. Recoverable oil reserves from the field are approximately 70 million barrels, making Kittiwake one of the smallest North Sea fields to be developed as a standalone facility. Kittiwake was originally part of the Gannet Cluster project which was suspended during the 1986 oil price collapse. It has now been developed using a 4 leg lift installed jacket which supports an integrated deck, living quarters module and drilling mast. The platform has 16 well slots, facilities for up to 36000 barrels of oil production per day, and accommodation for 80 men. Oil is exported via a 2km. long 8 inch diameter pipeline and a loading buoy into shuttle tankers. The Kittiwake tankers are dynamically positioned, enabling them to continue loading oil in rougher seas than moored tankers - an important advantage as Kittiwake has no storage and therefore is shut down when the tanker is not loading. Associated gas is exported via a 2km. long 4 inch diameter pipeline into the nearby Fulmar gas line. The Kittiwake jacket, which had a lift weight of 5400 tonnes, is supported by twelve 2.134m. diameter skirt piles each driven to 60m. seabed penetration. The jacket framing is depicted in Fig. 1. The four leg structure stands 106.6m. tall and directly supports the 7000 tonne lift weight integrated deck without an intermediate module support frame (MSF). The bracing pattern is very simple, having three X-braced vertical frames and four diamond braced horizontal frames at elevations +14m., -15m., -47m., and -82m. respectively. The nominal lateral dimensions of the jacket are 25m. by 22.6m. at the top, and 38m. square at the base. These plan dimensions are unusually small for the support of a large integrated deck, as Fig. 1 illustrates. After initial jacket design by Shell Expro, detailed design was undertaken by Earl & Wright, London. RGC, Methil then fabricated the jacket and piles. Installation of the complete platform was performed by HeereMaC using the semi-submersible crane vessel (SSCV) DBI02, under subcontract to McDermott International Inc. It is noteworthy that many of these companies were also principal players in the execution of Shell Expro's Auk project.