Late in the evening 20 April, an explosion rocked the deck of the Deepwater Horizon and set off a fire that raged for 36 hours before the Transocean semisubmersible plunged to the seafloor 5000ft below. As OE went to press, operator BP and other responders were working to staunch the flow of crude from the damaged well – at rates estimated by BP to be 1000b/d and by NOAA five times that – threatening the Gulf of Mexico coastline. Russell McCulley reports.
The full environmental impact of the Horizon fire and oil spill was still unknown at press time, but it was more than clear that the disaster would go down as one of the worst offshore incidents in US waters. Search and rescue teams failed to locate 11 missing crew members – nine Transocean employees and two workers from MI-Swaco – who reportedly were working in the vicinity of the blast. Of the 115 people who evacuated the rig, 17 were hospitalized with injuries.
Initial reports that the damaged well was leaking no hydrocarbons proved premature, and one week after the incident an oily sheen mixed with pockets of emulsified crude covered much of a 45-mile by 100-mile stretch of the Gulf of Mexico about 20 miles offshore Louisiana.
The US Coast Guard and Minerals Management Service had launched an investigation and would not speculate about what may have caused the explosion and fire aboard the rig, which was plugging and abandoning an exploration well at the BP-operated Macondo prospect in Mississippi Canyon block 252.
On 27 April, the investigation widened to include the US departments of Homeland Security and the Interior, which administers the MMS.
‘We will remain focused on providing every resource we can to support the massive response effort under way at the Deepwater Horizon, but we are also aggressively and quickly investigating what happened and what can be done to prevent this type of incident in the future,' said Interior secretary Ken Salazar.
BP dispatched ROVs in an attempt to activate the well's blowout preventer and had mobilized at least one drilling rig, Transocean's Development Driller III, as the company prepared to drill two relief wells, said BP chief operating officer Doug Suttles. Teams of four ROVs had not been successful in stopping the flow of oil at press time, and the Coast Guard was set to begin controlled burning of oil collected at the surface as the slick crept closer to wildlife refuges on the Louisiana and Mississippi coasts, Rear Admiral Mary Landry said during a joint press conference 27 April.
‘This is a serious spill,' Landry said. ‘If we don't secure the well, then, yes, this could be one of the worst oil spills in US history.'
Suttles said the normal series of defenses on the Cameron-manufactured BOP had failed to activate, prompting engineers to devise a number of new methods in hopes of shutting off the flow. In addition to the planned relief wells, BP was hurriedly constructing a device that engineers hoped would collect the oil in a dome at the seafloor and pump it to the Transocean drillship Discoverer Enterprise above. ROVs detected two leaks in a riser that failed to detach from the wellhead and was lying on the seafloor.
Suttles said it would likely be weeks before the equipment could be deployed. ‘I want to be careful with expectations,' he said. ‘This has never been done in 5000ft of water before.'
Meanwhile, Diamond Offshore Drilling evacuated more than 100 employees from the Ocean Endeavor, which was on location at Mississippi Canyon block 211 about 10 miles northeast of the Horizon. The rig was doing a workover at ExxonMobil's Mica gas field at the time of the explosion, said Diamond Offshore director of investor relations Les Van Dyke. ‘It wasn't an emergency or anything, just an abundance of caution,' Van Dyke said of the evacuation.
Landry said no other offshore installations had shut down in the week following the fire.
Plans call for the first relief well to be drilled to a total depth of around 18,000ft about a half-mile from the exploration well, which reached 18,300ft TD. The wells would be one of several ‘multiple streams' by which responders would seek to secure the well, Suttles said.
‘We will not stop until we exhaust every single option,' he said.
The remains of the Horizon settled on the seafloor about 1500ft northwest of the wellhead. Landry said an estimated 700,000 gallons of diesel fuel stored on the rig appeared to be ‘secure and stable'. The response team planned to send ROVs in for a more thorough examination of the rig in coming days.
At press time, response teams had recovered about 3740 barrels of oil and water mix and had 50 vessels, including skimmers and barges, on site for cleanup and containment operations. A total of eight ROVs were ‘working on the subsurface issues', Landry said.
Two pipelines in the immediate area were shut down as a precaution shortly after the fire began. An MMS spokesperson said the sunken rig had not come in contact with any subsea infrastructure.
Built in 2001 and rated for drilling in water depths up to 10,000ft, the Deepwater Horizon had undergone several routine MMS inspections in recent months, including one about two weeks before the explosion, the agency said. The rig set a record last year for the deepest oil and gas well while working for BP at the Gulf of Mexico Tiber prospect. The well reached 35,050ft in depth in 4130ft of water.
BP contracted the rig for three years in September 2007; last year, the operator extended the contract for another three years for around $544 million. OE