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Spotlight

Subsea Solutions at Macondo

Wed, 01/25/2012 - 17:05

In December 2011, Cameron agreed to pay BP US$250 million to indemnify the company for current and future compensatory claims, bringing an end to the lawsuit brought by BP which claimed that Cameron’s blowout preventer failed to stop the Deepwater Horizon spill, as a result of having a flawed design.

After conducting an investigation into the incident, Det Norske Veritas, the company hired to investigate the spill by federal authorities, concluded that after the well blowout, Cameron’s blowout preventer failed to stop the leak despite being successfully activated, not because of human error but because the technology encountered a situation for which it was not designed.

A blowout preventer is used as a last line of defence in the case of a spill. It works by using valves to close off the oil flow when the pressure gets too high, and as a final contingency, closes the well by cutting through the pipes with a series of hydraulic shear rams. The Deepwater Horizon blowout preventer had five of these shear rams, but all of them failed to stop the flow of oil as a result of a ‘buckled’ section of drill pipe that was moved sideways by the pressure of the oil flow.

When workers aboard the Deepwater Horizon first detected problems with the well, they activated parts of the blowout preventer designed to clamp around the drill pipe and cut off hydrocarbon flow from around it, but did not activate the shearing rams. However, by this time natural gas had already escaped from the well, and when it reached the surface this caused the explosion at the rig as the gas ignited, killing 11 workers and cutting off the power supply to the rig. This meant that engineers left on the rig were unable to activate the shearing rams to try and seal the well.

Two days later, it was a remotely operated vehicle (ROV) that managed to engage the shear rams on Cameron’s blowout preventer, but unfortunately, because of the position of the drill pipe, it was not fully sheared, and the rams failed to fully close and seal. The distance by which the shearing rams failed to close was tiny, at 3.6cm or less, but this was enough for oil to continue to escape from the well.

The investigation concluded that even if the shear rams had been correctly activated before the crew of the Deepwater Horizon abandoned ship, the buckled drill pipe would still have caused a problem for the shear rams. The report concluded that it was not misuse of the blowout preventer that caused the accident, or poor maintenance, but rather that the design was flawed in that it was not prepared to deal with the eventual state of the drill pipe that it was meant to sever.

As a result, companies that provide blowout preventers to the deepwater oil and gas industry have looked to increase the pressure their systems can provide in order to guarantee that the shear rams will be able to close despite the pressure being exerted upon them.