And yet the risks posed by deep-sea operations – and specifically the potential impact of the failure of key systems – have long been understood. In 2000, the US Department of the Interior’s Minerals Management Service (MMS) published a report warning that there were several difficulties connected with deep-water well control, that experience in this area was “limited” and with many rigs having very high oil production rates, a blowout could be “a potential show-stopper” for deep-water drilling in general. That may yet prove to be the case.
Environmental waiver
Four years later, a report prepared for the MMS by a team at Texas A&M University in College Station warned that while drilling technology had advanced, safety technology had stagnated – and highlighted blowout control as a particular concern.
Then in 2008, a Society of Petroleum Engineers report warned that the hydraulic rams used in many BOPs to shut off oil flow may lack the capacity to cut through the high-strength drills used in deep-sea operations. The report’s authors included people employed by Transocean and BP – the companies that own and lease Deepwater Horizon respectively.
Despite these reports, in 2009, the MMS granted BP’s Deepwater Horizon drilling operation a “categorical exclusion” from all environmental reviews under the US National Environmental Policy Act. Such exclusions are meant for projects where, if any problems occur, environmental damage is likely to be minimal or non-existent. Until this month’s spill, the MMS had granted hundreds of such waivers each year to drilling operations in the Gulf of Mexico.
“It is unfortunately a very common practice and in this case it had catastrophic results,” says Kierán Suckling, executive director of the environmental group Center for Biological Diversity.
Stopping a blowout
The BOP is a massive stack of high-pressure valves, in this case weighing 400 tonnes, that sits on the sea floor and is designed to stop an uncontrolled release of oil or gas from a well during the initial drilling. At the bottom of the device are shear valves or rams designed to cut through the drill pipe and block off any oil flowing inside the pipe or through the surrounding well casing. Higher up the stack, annular rams are clamped onto the outside of the drill pipe, to reduce oil flow by tightening the ring-shaped space between the outer well casing and the inner drill pipe.
The BOP beneath Deepwater Horizon had a number of mechanisms to activate both sets of rams, including a manual emergency shut-off on the drilling platform 1500 metres above the sea floor. It also came with sensors that would automatically activate the rams in the case of a rapid increase in well pressure. Additional sensors in the pipe running from the sea floor to the drilling platform were designed to activate the rams if pipe and platform ever separated.
“We don’t know why it didn’t work,” says BP spokesman William Salvin. “We know automatic systems did not close it, we know workers hit the manual switch before evacuating the rig, and we have been trying since hours after the incident to activate the blowout preventer [using remotely operated vehicles] and that has not been successful.”
Containment dome
With the BOP failing, the options open to BP are limited. Other steps to stem the flow of oil are both slow and unproven. The approach that BP is trying at the moment is to cover the well head with a containment dome – a 12-metre-tall steel box with a funnel-shaped top leading to a relief pipe to channel the oil to the surface. Such domes have been deployed in shallow waters, but never previously at such depths.
One of the challenges is the intense water pressure. “Navy submarines, for example, are crushed at 900 metres. We are working at 1500 metres; this is a very difficult technological challenge,” Salvin says. BP’s initial attempts this week have been confounded, the company says, by a build-up of methane hydrate crystals blocking the relief pipe.
BP’s next fallback is a relief well, which it started drilling last week. Eventually this should intersect the original well near its origin, some 4000 metres below the sea floor, and then be used to flood it with mud and concrete to stop the uncontrolled flow. However, it could take up to three months to complete the job.
“It may take a number of tries but you can do it,” says Ken Arnold, an oil industry consultant based in Houston, Texas. He adds that a GPS tracking device, as well as acoustic and magnetic field sensors, can be mounted behind the drill bit of the relief well to help pinpoint the existing well.
What next?
So what more could have been done to prevent such a disaster in the first place? Adding a second BOP or placing a containment dome above the BOP – ready to deploy in case of failure – may have helped. But these could make rigs more complex and more vulnerable to human error, Arnold warns. “Rushing to add more tests or redundancies on the system may be the wrong thing to do.”
Suckling doubts that any deep-sea drilling can be safe. “Government and the oil industry have said for many years these wells are safe, but all technology eventually fails and if the cost to mitigate that failure is prohibitively expensive, you don’t go forward,” he says. “Are we willing to put entire ecosystems and the economies of several states at risk? I’d say no.”
Cleaning up the mess
BP and federal officials are employing a variety of clean-up techniques to limit the environmental impact of the massive oil spill from the Deepwater Horizon disaster.
One of the primary tools is the use of dispersants, which work much like the detergents in washing-up liquid used to break down grease. The key ingredient being used in the Gulf of Mexico is a sulphonate, a surfactant that binds to both water and oil, reducing the surface tension of the oil. Solvents, including propylene glycol and 2-butoxyethanol are also being used to increase the dispersant’s ability to mix with the oil. With help from the ocean’s natural wave action, the reduction in surface tension allows large surface slicks to separate into individual droplets that eventually sink to the sea floor.
“It’s a trade-off,” says Carys Mitchelmore of the University of Maryland’s Chesapeake Biological Laboratory in Solomons. “Dispersants take oil off the surface and keep it away from wetlands and other sensitive shoreline habitats where it can cause contamination for years.” But the suspension of tiny droplets in the water column and their eventual build-up on the sea floor can create problems for filter feeders such as mussels and oysters, corals and shrimp larvae.
“Fish can ingest oil particles that then stick to their gills. It’s like coating our lungs in oil: they aren’t going to breathe too well and we wouldn’t either,” Mitchelmore says.
Since the spill began, clean-up crews have deployed over a million litres of dispersant on the surface and are now testing the chemicals on the sea floor at the source of the leak. Dispersant application at such depths has never been tried before and researchers are unsure how well it would mix with oil in the cold, high-pressure environment at that depth and in the rising oil plume.
“Dispersants need wave action, typically. This is a forceful plume but I have no idea how well that process will work,” Mitchelmore says.