Geoffrey Maitland: 'Top kill' with heavy fluid could stem the flow

The current solution is the so-called "top kill". Kill is the term used to stop the flow from the well and they're trying to do this by injection of fluids into the top of it.

The "blow out preventers" (BOPs), large valves designed to shut off the top of the wellbore when there's an incident, did not work fully. The plan is to counter the oil and gas pressure by injecting a heavy, high-density fluid into the well. Because the BOPs are partially open, the question is how much of the heavy density fluid will go down and how much is going to come up and flow out of the open BOPs. BP will try to pump enough of this heavy fluid in so that there is eventually a long enough column of fluid that exerts a downward pressure which is greater than that of the oil and gas which is trying to get out.

There's been quite a delay in getting ready for this. They have to take lines down from the drill ship to the sea bed and connect them up to the "kill and choke" lines below the BOPs using remotely operated vehicles. Getting this in place takes some time. They are now doing some small injections of fluid into the BOP to try to monitor at what pressures they need to inject.

If they can pump enough fluid in – and they keep emphasising that this has never been done at 5,000 feet below the sea – they should be able to stem the flow. That fluid will sit there, keeping the oil and gas at bay. They will then be able to displace some of the fluid at the top of the well with cement slurry which will set to create a permanent plug. The chances of creating further leaks with this operation are slim and would only occur if the kill and choke lines couldn't be closed again after the operation and became disconnected from the lines to the drillship. This worst-case scenario might then create another couple of leaks.

Geoffrey Maitland is professor of energy engineering at Imperial College, London