Development Of Shuttle Tanker Loading Systems In The Norwegian Sector Of The North Sea

Abstract

ABSTRACT The bow loading systems developed for the Norwegian sector are relatively sophisticated. Continuous improvement in the designs has taken place. Several of the components we have developed have new advanced features:Chain stopper releasable up to the chain breaking load.Crude oil coupler for engagement with self closing hose termination piece.Drum with radial rope outlet which eliminates chafing contact.Cardan suspension of the crude oil riser which allows both the use of conventional pipe swivels and a load cell carrying the complete riser load. All crude oil transported from the Norwegian sector of the North Sea passes through the above system. This system is also used in the British sector and in the first loading system offshore Nova Scotia. The number of offloading operations has passed 4000. INTRODUCTION The weather conditions in the North Sea are harsh and the strain on the mooring and crude oil transfer equipment is considerable. In the Norwegian sector there has been a continuous development of the shuttle tanker loading systems. This development is carried out partly to counteract heavy strain, but the main reason for the modification of the tanker loading systems is changes in the loading buoy design. LOADING BUOY TYPE AND CHANGES Fig. 1 shows the location of the various crude oil fields with shuttle tanker loading facilities. The present, and some future such fields, are summarized as follows: Crude oil loading from two CALM buoys was started at Ekofisk in July 1971 and terminated in October 1975 when the pipeline to Teeside was put into operation1,4 In 1978 the first articulated loading platform (ALP) at Statfjord was put into service and later four similar buoys installed, two at Statfjord and two at Gullfaks. The two first Statfjord buoys were later replaced by subsurface loading buoys without mooring facilities (UKOLS). On the Oseberg field the test production phase 1986–88 was carried out by means of a PTS vessel with stern offloading facilities. A pipeline to Sture took over the crude oil transport. On Haltenbanken further north in the Norwegian Sea a floating loading platform will be installed on the Draugen field in 1993 and two subsurface buoys for turret mooring and oil transfer are intended for the Heidrun field. SHUTTLE TANKER BOW LOADING SYSTEMS The shuttle tanker loading systems used to date in the Norwegian sector of the North Sea are bow loading systems (BLS), i.e. both the hawser and the hose are connected to the tanker bow section. The hawser connection for these shuttle tankers are in the vessels centerline. The position of the hose connection is in the centerline below the hawser connection on the Statfjord and Gullfaks tankers, and on the port side of the forecastle deck for the remaining systems. EKOFISK TYPE1,2,4 A "self-mooring" system was specified for the shuttle tankers. The 12 inch circ. floating polypropylene messenger was picked up by a grapnel, hoisted through the SPM fairlead and connected to a dummy line from a traction winch.