The oil spurting from the seafloor beneath the destroyed Deepwater Horizon drilling rig is fast becoming one of the worst spills ever seen in the Gulf of Mexico, threatening wildlife both at sea and on the nearby coasts, as well as casting a shadow over President Obama's recent go-ahead for expanded oil and gas drilling around the US. But what can be done to stop the oil flowing?
What happened to the blow-out prevention system?
This system sits on the seafloor and clearly failed to protect the rig. But, explains Geoff Maitland, professor of energy engineering at Imperial College London, there will still be three or four "rams" than could be operated to cap the well. One aims to simply plug the pipe, another inflatable steel and rubber system aims to do the same, while a third aims to cut right across the pipe in case the pipe itself is damaged. The fact that submarine robots have failed to operate the rams yet suggests either the system was destroyed in the blowout, or that the gushing oil means the submersibles can neither see or hold their position well enough to work.
What about putting a funnel over the well?
This can be done using a steel collector, which needs to be secured over the well. BP says it is constructing a 100-tonne steel funnel but warns the technology has never been tried below a few hundred metres - the Deepwater well is 1,500m down. If the currents and visibility did not prevent putting the funnel in place, it would lead to a pipe taking the oil, gas and seawater to the surface for separation and storage. The funnels need to be constructed to order, meaning more delays, probably of 2-4 weeks.
Can a new well be drilled?
It can, and BP are working on this, but it is is likely to take several weeks at least. A hole could be drilled down at an angle to intercept the existing well, from about half a mile away. Or a new hole could be drilled into the reservoir to relieve the pressure and reduce the flow from the blown-out well. That would make capping the well easier. At the seafloor, the pipe would be about 100cm wide, but at depth the well would be smaller, but engineers can drill with great precision.
Can the oil be burned off?
BP have tested burning some oil, but the success of this approach depends on largely on the weather. Rough seas, as have been seen, mix the oil with water, meaning it burns much less well. Winds also disperse the oil, making it harder again. If burning can be done, the solid tar that remains is easier to scoop up in nets than liquid oil. However Martin Preston, a marine pollution expert at the University of Liverpool warns that burning the oil can leave a very persistent residue that can be more resistant to natural breakdown. He advocates continuing to use chemical dispersants, provided supplies hold out.
Can the oil be coralled by booms and collected?
BP said more than 30,000m of boom had so far been assigned to contain the spill, with an additional 87,000m available and 97,000m on order. Again, the weather is the key.
What is the best option?
All of the above done in parallel, according to Maitland.