Recovering oil from the Deepwater Horizon spill

In the immediate aftermath of the explosion and fire on the Deepwater Horizon (DWH) oil rig, BP activated its two Oil Spill Response Organisations (OSRO). Without delay, both organisations mobilised the equipment they had available in the Gulf of Mexico, including offshore recovery equipment, considered to be the best in the US, in the hope that these resources would be able to contain and recover the oil from the MC252 well before it could affect sensitive areas of the shoreline.

Rapidly, as the spill escalated and vast quantities of oil escaped from the offshore recovery system, the efficiency of the equipment deployed was called into question. Recovery at sea was considered less effective than anticipated. The sea state, even when fair, hindered operations. Encounter rates were low, with some skimmers being unsuitable for the type of oil or unable to operate in the large, thick slicks of fresh oil around the well. When modern devices were eventually imported from Europe, and deployed alongside the American devices, they proved to be capable of operating in rough seas and recovering larger quantities of oil.

For slick containment and recovery, in total over 6,000 vessels were mobilised, forming a fleet including tugs, barges and oil spill response vessels fitted with specialised equipment (floating booms and skimmers), as well as a fleet of fishing vessels contracted by BP. The extensive involvement of fishermen partially compensated for their loss of revenue. Some of them directly contributed to in situ burning operations, but the majority were tasked with supporting containment and recovery operations at sea, as well as towing sorbent booms in inshore waters. Mechanical recovery resulted in the collection of around 224,000 metres cubed of oilwater mixture representing, after settling, 3 to 4 percent of the crude oil spilt and according to estimations, between 8 and 15 percent of the emulsified oil present at the sea surface.

Difficulties encountered

Offshore competition with dispersant application and in situ burning and inshore competition with the protection of sensitive sites penalised recovery in a number of ways: by not always allowing access to areas where it could have been the most efficient option (thick slicks treated by other methods); by not always providing appropriate aerial guidance means (to remain in contact with the thickest parts of slicks, to work for as long as possible each day); by not providing optimal logistics, in particular in terms of vessels of opportunity (VOO).

Offshore recovery

A week after the rig sank, the offshore recovery branch consisted of 26 vessels capable of working in deep water, seven dedicated tug boats and three offshore oil storage barges. In total, over 60 offshore skimmers were used at the height of the response, mainly deployed by 12 specialised vessels and several US coast guard vessels.

This capacity to mobilise resources is seen as a resounding success by the oil industry, yet the offshore response faced several limitations. For safety reasons, operations could not be implemented less than nine kilometres (five nautical miles) from the source, meaning that vessels were responding to thin slicks and therefore performed relatively poorly. Operations were also limited by the sea state, with most skimmers, as well as the associated booms, unable to operate beyond sea state three.

Equipment management

The large-scale influx of equipment rapidly required it to be identified, inventoried, deployed and monitored. The lack of an exhaustive database updated in real time for all the equipment available to the OSROs in the US was a limiting factor for the organisation of operations.

 

 

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Georges Peigné, deputy director, Cedre, Brest, France
Edition: Edition 57

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