‘Top kill' success reported

Narayan Lakshman

Washington: After 37 days of failing to halt a torrent of oil spilling from its damaged offshore rig into the Gulf of Mexico, engineers from rig owner British Petroleum and other agencies reportedly stemmed the flow using a “top kill” operation that choked off the leaking pipe with drilling fluids.

Quoting United States Coast Guard Admiral Thad Allen, who is leading the effort to curtail the spill, the LA Times newspaper reported on Thursday morning that “industry and government engineers had pumped enough drilling fluid to block oil and gas spewing from the well… [and the] pressure from the well was very low but persisting.”

The next step in the operation would be to pump cement into the hole to entomb the well, to prepare for which, Admiral Allen said, engineers were also pumping some debris into the blowout preventer at the top of the well.

However, neither the administration nor BP has yet commented on whether or not the flow of over 5,000 barrels of oil per day from the damaged MC252 offshore well had been stopped.

Earlier Ken Salazar, U.S. Secretary of the Interior, had said, “We will keep our boot on their neck until the job gets done. And… we will make sure that all of their responsibilities are fulfilled to the people of the Gulf Coast and to the U.S. government.”

The early reports of success surfaced even as the Obama administration came under a barrage of criticism for failing to act decisively to stop the leak and clean up the massive environmental damage that has already occurred. Significant loss of animal and plant life as well as the livelihoods of shrimp farmers, for example, has been widely reported for weeks now, along the fragile coastal marshlands of Louisiana.

Under rapidly mounting political pressure, the President was poised to announce extension of a moratorium on deep-water offshore drilling for a further six months, according to reports that quoted the White House.

According to Reuters, Mr. Obama “will announce standards to strengthen oversight of the industry and enhance safety, a first step in a process that the independent Presidential Commission will continue.”

The White House was further reported to have indicated that Mr. Obama would announce the cancellation of drilling leases for projects off the coast of Virginia and delays in both exploration and drilling off the coasts of Alaska.

In a further fallout from the crisis, it was reported that Elizabeth Birnbaum, Director, U.S. Minerals Management Service — which oversees offshore drilling — had been fired.

Oil spill: what is a ‘top kill'?

Finlo Rohrer

BP is using a “top kill” procedure to stop the Gulf of Mexico oil spill.

But what exactly is “top kill”?

One way to think about “top kill” is to imagine something sitting on a spring. Put a heavy enough weight down on the spring and it will be squashed down. But put something on that's too light and the object will be thrown off.

In this case, the “spring” is oil and gas coming out of the reservoir, beneath the sea, at the site of the well drilled by the Deepwater Horizon and at pressures exceeding2,268 kg per square inch.

The “top kill” operation will involve pumping “heavyweight drilling mud” from a number of ships through the command vessel on the surface, the Q4000.

The mud will be pumped down a “drill pipe” from the Q4000 and into a manifold — a unit with converging pipes — on the sea bed.

From there it will be primarily pumped into the kill and choke pipes that connect to the blowout preventer — the unit that sits on top of the oil well.

If the density of the mud — and the pressure of the pumping — is right, it will pass through the blowout preventer and then inside the top of the well and with its downward pressure will stop the flow of oil and gas gushing from the reservoir beneath.

Permanent seal

“It is like two forces fighting with each other. If the force downwards exceeds the force upwards, you are going to succeed,” said Iraj Ershaghi, director of the petroleum engineering programme at the University of Southern California. If this has happened, the well is “killed” The leak will be completely stopped, but this will only be a prelude to a permanent seal using cement.

The procedure has been carried out many times around the world but, as BP admits, never at anything approaching this depth. In 50 ft of water, divers would be doing much of the complicated work of checking pipes and connections.

But all the work on the Deepwater Horizon's well is being carried out by Remote-operated Vehicles (ROVs), making everything much more difficult. And there could be a major difficulty, said Prof. Ershaghi. The assumption behind the “top kill” plan is that the leakage is all coming out of the riser connected to the top of the blowout preventer.

“If this was not the case, such as if there are leaks around the conductor casing, or if the intermediate casing strings are not cemented in place adequately, a burst of a certain portion of the casing could occur and the ‘top kill' may fail,” said Prof. Ershaghi, who spent the early years of his career as an engineer in the Bahregansar oil field in the Middle East. “Some of us suspect that the problem is more serious than simply a kill operation.”

Further danger

The well itself has been drilled into a geological formation. Inside the “hole” there is a steel casing, and the gap between the casing and the formation — the annulus — is filled with cement. If the cement job is not adequate, leaks can occur behind the casing and oil and gas can find their way to the sea floor, or can also cause a collapse of unprotected parts of the casing at shallower depths. If that cement has leaks, then oil and gas could be escaping into the water to the side of the blowout preventer, said Prof. Ershaghi.

It would not be easy to see if this was happening, he explained. “When you have 5,000 barrels (795,000 litres) of fluid coming per day, you need better ROV camera shots otherwise you cannot pinpoint the sources of leaks.”

Even if BP's experts are right and all of the oil is coming through the blowout preventer, the “top kill” could still fail.

It could even start increasing the leakage of oil, by as much as 5—15 percent, if the high density mud ends up bursting segments of the casing. For some engineers, it is simply impossible to speculate on the chances of success. “I would hate to venture a guess,” said Lloyd Heinze, professor of petroleum engineering at Texas Tech University. “[It is] a procedure described in training scenarios [an] established procedure, not well-known, not the ideal way of trying to kill a well because it is not an easy way to do it.”

But he said only BP would know the chances of success, as engineers around the world would not know the calculations the firm's experts had undertaken.

If the “top kill” fails, BP will then move on to other plans. It has prepared something called a lower marine riser package (LMRP). This device would sit on top of the blowout preventer.

Other options such as a “junk shot,” where a flurry of rubber objects and other material is pumped into the blowout preventer to block it, are also on the table.

But every engineer involved will be crossing their fingers that the “top kill'' works, and makes engineering history.

— © BBC News/Distributed by the New York Times Syndicate