Control of the ship was lost inside the 500-metre safety zone which surrounds the Ekofisk Complex, and it ploughed ungovernably between installations and under bridges until the collision. Nobody was injured, but the powerful bump did major harm to the platform, the bridge linking Ekofisk 2/4 X and 2/4 C, well equipment and the vessel itself.
The damage to structure and wells was so extensive that ConocoPhillips decided to shut the installation down completely and permanently plug the wells. Both 2/4 W and the wells were due to be replaced in any event, but no date had been set when the accident occurred.
As noted above, Big Orange XVIII was a multipurpose vessel built in 1984 and specially equipped to conduct well stimulation work. It measured 74 metres long by 18 metres wide, and weighed 5 000 tonnes. With 21 people on board, it was on its way to stimulate wells on Ekofisk when the accident happened.
For its part, 2/4 W was a combined bridge support and water injection facility installed on the field at early as 1972. With three steel legs, it was usually unmanned – on this night as well.
The Petroleum Safety Authority Norway (PSA) described the collision as serious, with the potential to become a major accident. This was defined as an incident involving several serious personal injuries or deaths, or posing a threat to the integrity of an installation.[REMOVE]Fotnote: Petroleum Safety Authority Norway, Gransking av Big Orange XVIIIs kollisjon med Ekofisk 2/4-W 8.6.2009, 2 October 2009.
The second mate, who was on his first voyage with Big Orange XVIII, stood on the bridge when a call came from Ekofisk to prepare for well stimulation. He notified the captain, who arrived and took over command before contacting Ekofisk for permission to enter the 500-metre exclusion zone. Such authorisation is mandatory. The captain turned off the autopilot to begin manual manoeuvring, as required by the regulations. Then the phone rang, and he left the bridge to answer.
First, however, he reactivated the autopilot – a move which proved crucial for subsequent events. After taking the call in the radio room, the captain returned to the bridge – but forgot the autopilot. The ship was making 8.4 knots, which exceeded the maximum speed of eight knots in the safety zone. When the captain tried to slow down, however, he got no response because of the autopilot.
Big Orange XVIII thereby passed out of control under the bridge between Ekofisk 2/4 X and the bridge support, and narrowly avoided hitting 2/4 FTP and the COSL Rigmar rig next to it. The captain put the thrusters into full reverse, but they also failed to respond. Instead, the ship’s speed increased to 9.7 knots until the collision occurred.
With its fire alarm activated, the ship swung round and laid itself under the bridge between 2/4 W and 2/4 FTP. The engines finally shut down after someone pressed the emergency stop button.
Once the position had been brought under control, 2/4 W shut down and the man-overboard (MOB) boat launched, preparations were made to tow Big Orange XVIII to a safe place. The ship’s engines were re-engaged and the vessel backed away from the platform. Another collision then occurred, this time with the Northern Crusader stand-by ship which had arrived to help.
Both vessels suffered minor damage aft, but a towline was passed between them and Big Orange XVIII could be towed to a safe place near Albuskjell.
While the ship had equipment torn off and its bow staved in by about two metres, 2/4 W was pushed partly out of position and several of its braces were loosened. One of the water injection risers was heavily bent, several wellheads were displaced and a number of other hurts were eventually discovered.
ConocoPhillips came in for criticism after the accident for failing to monitor activity within the safety zone to an acceptable level. It was also censured for not following up the measures which had been proposed after a similar incident in 2005. Ocean Carrier then collided with various Ekofisk structures in a calm sea but dense fog. See the separate article.
In its investigation report, moreover, the PSA called attention to another accident which it felt the owner and captain on Big Orange XVIII should have learnt from. Supply ship Far Sympathy had collided in 2004 with the west Venture rig on the Troll field further north, and the investigation found the autopilot had not been disconnected. In addition, the officer of the watch on Far Sympathy had not complied fully with the checklist when arriving at the 500-metre zone. That would have revealed that the autopilot was on.[REMOVE]Fotnote: Letter from Hydro Oil and Energy to the Petroleum Safety Authority Norway concerning investigation report, 19 March 2004.
The Big Orange XVIII accident on Ekofisk was no one-off. In 2011, the PSA expressed concern over collisions with offshore installations by visiting vessels. No less than 26 of these had occurred off Norway in 2001-11 because of failures in organising work and responsibility, inadequate training and faulty equipment.[REMOVE]Fotnote: Petroleum Safety Authority Norway, Risiko for kollisjon med besøkende fartøyer, 5 January 2011. Downloaded from http://www.ptil.no/konstruksjonssikkerhet/risiko-for-kollisjoner-med-besokende-fartoyer-article7484-826.html.Upset stomachs on EkofiskAirborne ash stops flights