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NAVY DIVERS FAIL TO FIND SURVIVORS IN CAPSIZED OIL RIG TUG

Adapted from various sources: 14 April 2007

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ROYAL NAVY divers entered the submerged Bourbon Dolphin three times on Friday but found no signs of life.

The Norwegion oil rig support tug had capsized in the North Sea off Shetland the day before (12 April 2007). Only seven of the 15 crew survived and were picked up by rescue helicopters.

Capsized Bourbon dolphin Shetland Islands map

The Bourbon Dolphin had been moving one of eight anchors that pin down the Transocean Rather oil rig. It is thought that the anchor chain, attaching the tug to oil rig, may have tightened, pulling it over.

Anchor handling is generally regarded as one of the most hazardous offshore activities, because of the risk to crew on the deck. However, capsizing has not - till now - been regarded as a threat.

Boubon dolphin afloat

Bourbon Dolphin before the tragedy. The tug was less than one year old.

BACKGROUND INFORMATION ON OIL RIGS:

(1) FOUR TYPES OF OIL RIG IN USE

Platform rig

PLATFORM. This immobile structure can be built from concrete or steel and rests on the seabed. When oil or gas is located, a platform may be constructed to drill further wells at that site and also to produce the hydrocarbon. Although some platforms can be small, most are massive compared to the other types of installations.

Semi-submersble rig

SEMI SUBMERSIBLE. This floating drilling unit has pontoons and columns that, when flooded with seawater, cause the pontoons to submerge to a predetermined depth. Although it is moved by wave action, it sits low with a large part of its structure under water. This, combined with eight huge mooring anchors, make it a very stable installation and the preferred choice for exploring the North Sea and the new wells west of Scotland.

There can be over one hundred people on board and, although smaller than a platform, conditions are usually good.

This type of rig drills a hole in the seabed then it moves to the next location. There is often an urgency to get things done quickly. With advancing technology some semi submersibles can drill in water depths over five thousand feet.

Jack Up rig

JACK UP. This is a mobile drilling rig. Instead of floating over its drilling location LIKE A semi submersible, the Jack Up has long leg structures, which it lowers to and then into the seabed. This raises the rig out of the water. The use of legs means that this type of installation can't operate indeep water: the maximumis five hundred feet. Luckily however, many areas of the North Sea are not too deep for Jack Ups to operate.

Drill ship

DRILL SHIP. As the name suggests this is a ship shaped drilling vessel. Unlike the semi submersible and the Jackup, it does not require tugboats to tow it to location. Although they are not as stable as semi submersibles they also drill in very deep waters.

(2) SOME OIL RIG ACCIDENTS SINCE 1979

Rig: Sedco 135F Triangular Semi-Sub Date: June 1979 Location: Bahia de Campeche, Mexico Operator: Petroleos Mexicanos (PEMEX) -->	In 1979, the Sedco 135F was drilling the IXTOC I well when the well suffered a blowout. Due to the massive contamination caused by the spill, nearly 500 aerial missions were flown, spraying dispersants over the water. Prevailing winds caused extensive damage along the US coast. The IXTOC I accident was the biggest single spill ever, with an estimated 3.5 million barrels of oil released.
Rig: Steelhead Platform Date: December 1987 Location: Cook Inlet, Alaska Operator: Marathon Natural gas as from a shallow gas pocket began to escape during drilling and the gas eventually ignited. The fire burned out of control for a week before the well was bridged and the fire put out. The 49 crew on board managed to evacuate the rig. The heavily damaged platform was repaired, allowing production to be resumed.	Rig: Piper Alpha Platform Date: July 1988 Location: North Sea Operator: Occidental Fatalities: 167 The Piper Field was discovered 1973. The Piper Alpha platform, located about 120 miles north-east of Aberdeen, produced crude oil and, later, gas as well. One evening, condensed gas, leaking from a pump, exploded causing fires. Several more explosions followed and a big part of the installation's structure collapsed.
Rig: Ensco 51 Jack-Up Date: March 2001 Location: Gulf of Mexico Operator: Forest Oil Corporation -->	The well suddenly experienced an uncontrolled oil flow, causing a blowout and fire. During the fire, Ensco 51's platform and its equipment were also damaged, whilst the derrick and substructure were destroyed. (The derrick is a framework or tower, positioned over the drilled hole, and supporting the drilling equipment or piping.)
	In July 2003, Jack-Up rig AD-19 capsized and sank in Saudi Arabian waters. A salvage team recovered the sunken parts and redelivered them to their owners. They were then taken to a nearby yard for repairs. The photo above shows the submerged rig.