First oil cargo

Equipment to transfer the crude from platform to tanker had not been properly tested in advance, because a realistic trial would have required both oil and ship – neither of which were available until production had begun. So testing took place with the first cargo.

It was a complex system. Four large cargo pumps down in the utility shaft pumped oil via metering stations to the loading buoy and into the tanker. A lot of adjustment was needed. The pumps had to be tuned to provide the correct pressure and volume, and checks carried out with the metering stations, flowline and all the other equipment involved.

People were stationed everywhere – in the processing facilities, on the loading buoy, on the tanker, on deck and so on. Three pumps in all were to be set in motion.

The first was started up and the valves opened, and the tanker soon reported that it was receiving liquid ¬– initially just water which had accumulated in the system, and then crude. Everything seemed to working fine.

When the second pump was activated, however, the system began to become unstable and pressure variations arose. These caused powerful vibrations in the flowlines which ran through the utility shaft, through its wall and along the seabed to the loading buoy. The pipes shook, and the only option was to shut down. It transpired that the instability was due to a control valve which was not functioning as it should. Once that had been adjusted, the equipment was started up again. They carried on in the same way for almost 80 hours before the vessel had been loaded.

Transferring oil to a tanker proved a demanding operation. The storage cells always had to contain liquid, and the large volumes of oil being transferred had to be replaced by water. So as the crude sluiced out, seawater sluiced in.

That was another system which had not been tested in advance, and the sound it made when starting up was like a train rushing over the deck. The process operators were very uncertain whether they had this under control. Nobody had heard that noise from the facility before.[REMOVE]Fotnote: Interview with Einar Jensen by Trude Meland, Norwegian Petroleum Museum, 14 June 2010.

It was also wet and windy during the first loading operation. The shuttle tanker had arrived on 4 December, but a strong gale gusting to storm strength had blown up during the afternoon.

Conditions had deteriorated by midnight into a heavy storm gusting to hurricane strength, and the biggest waves were 16-25 metres high. The tanker pitched and rolled violently, but was nevertheless filled with the first consignment of 100 000 barrels from Statfjord.[REMOVE]Fotnote: Lindøe, John Ove. From Sea to Shore. Stavanger 2009, p 39.

The shuttle tanker employed for the first loading operation was called Polytraveller and had been specially designed to load from the Statfjord A buoy. Two powerful bow thrusters and a reversible propeller were invaluable for steering the ship up to the buoy.

 It could be manoeuvred from a small bridge right up in the bows, where equipment was also installed to connect the loading hose for oil to be pumped aboard. Since the top of the loading buoy rotated, the tanker could lie bows-on to wind and weather at all times.

To moor the tanker to the buoy, a pick-up line had to be taken aboard in order to haul in the actual hawser. An auxiliary vessel helped to secure this line for the first loading operation, but the tanker could have fished it up directly without problems – which was what happened with later loadings.

 When the mooring hawser had been pulled out of the buoy, a weight inside the latter was raised and locked in that position. Once loading had been completed and the tanker disconnected, the weight descended and pulled the hawser back into the buoy.

The termination of the loading hose, known as a Y-piece from its shape, was attached to the hawser and pulled on board with the aid of a winch. Once there, it was locked down and pumps on the platform transferred oil from the storage cells through a flowline on the seabed, up the buoy, along the loading hose and into the tanker’s cargo holds.

An essential step during transfer of the oil was to meter the volume being loaded. This was done with the aid of a propeller installed in the flowline. The faster the oil flowed, the faster the propeller turned and the results could be read off in the control room. This metering formed the basis for allocating the oil between the licensees and for calculating taxes.

The K/S Statfjord Transport a.s & Co limited partnership was responsible for transporting oil from the field. Operated by Statoil, it was owned by the licensees with the same proportionate interest they had in Statfjord.

This company had joined forces with Norwegian engineering company Pusnes Mekankiske Verksted and shipowner Einar Rasmussen Rederi to develop a tailormade system for loading oil in the open sea under fairly rough weather conditions.

Offshore loading was not an unknown technique – it had been used during early production from Norway’s Ekofisk field, for instance. But the new solution was the most advanced of its kind.

To learn more, see:  Start-up, initial production and first cargo