West Vanguard Blowout
According to Norwegian Petroleum Directorate records, Statoil's well 6407/6-2 was spudded by the Smedvig West Vanguard on 04 October 1985. The 36" top hole had been drilled down to 323m MDBRT with the 30" conductor set at 318m MDBRT. The blow-out preventer (BOP) had not yet been installed.
At around 2050 hours on the night of 06 October 1985 while drilling the upper Pliocene sediments of the 26" section, a drilling break was observed between 505-508m MDBRT with an ROP increase from 40m/hr to 712m/hr. Drilling was stopped at 523m MDBRT and the bit was pulled back 15m, after which the well began flowing and unsuccessful attempts were made to kill the well by pumping killmud. The bit had entered a shallow gas pocket at around 504m causing the well to blow out. A MAYDAY was sent from the rig at about 2310 and picked up by the Norwegian rescue center at Sola, which directed rescue ships and helicopters to the crew's aid.
With no BOP used for the top hole section, the flow of gas had been directed through the diverter system. This system was unable to contain the flow and the liberated gas exploded at around 2320 hours, engulfing the rig in a fireball. The one fatality is assumed to have resulted from this explosion, although reports indicate the victim's remains were never found. The rest of the crew were able to evacuate the rig in a matter of minutes using the fore lifeboats. The rig's deck structure, two of its legs and the engine room were damaged in the blast, resulting in the rig listing by 10 degrees.
By the following day, the fire had burnt out but gas continued to leak out of the well and bubble up to the side of the listing, fire-damaged hulk. Reporters flying over the rig noted a large hole in one of the rig's legs, extensive fire damage and a fallen crane.
After the accident, the rig was towed to Freifjorden near Kristiansund, Norway and investigated by Norwegian police and SINTEF (a Norwegian industrial research institute). The investigation revealed that gas initially leaked from the gasket between the riser and the slip-joint, forming a gas cloud on the cellar deck level which migrated into the shaker house via a poorly closed valve and travelled through an exhaust pipe, across the upper deck and into other rooms via air ducts before igniting. To quote the SINTEF report: 'Doors and hatches in and around the drilling module on the upper deck were knocked open in a pattern that gave indications of the course of explosions.'. The subsequent failure of the diverter system was attributed to the extreme flow of gas, drilling mud and sand, which eroded holes in pipe bends of the diverter system. Spurts of sand against the metal of the rig were suggested as one of the possible ignition sources of the gas cloud.
The rig was restored, returned to work and subsequently sold by Smedvig to Diamond Offshore Drilling Ltd. for US$ 68.5 million in December 2002. The rig was then renamed Ocean Vanguard, to fall in line with Diamond's rig naming policy.
After the blowout, Bergen Underwater Services (BUS) were contracted to locate the Vanguard's eight anchors, which had been cut and discarded to allow the Vanguard to be moved away from the gas blowout. BUS then deployed an underwater ROV from the M/V Arctic Surveyor to find the anchors. During the search, the ROV operator found a crashed World War II Heinkel He 115 on the seabed, which had been based at Trondheim, Norway during the Second World War. The plane had been cut in to two by the movement of one of the Vanguard's anchors. The full story of the Heinkel can be read at the NUAV Norway During WWII website.