BP aims to plug gulf oil well for good with two-pronged 'kill' shot
Monday, August 2, 2010
The next shot at killing BP's well in the Gulf of Mexico could begin as early as Monday night, as engineers plan to pump heavy mud into the capped but still dangerous well and "bullhead" the rogue oil back down into its source rock 2 1/2 miles below the seafloor.
The "static kill" is part of a double whammy of mud and cement that would hit the runaway Macondo well high and low in quick succession. The static kill starts at the top, firing the mud and possibly cement into the blowout preventer that sits on the wellhead. That effort, which would take a day or two, would be followed in another five to seven days by the start of the more laborious "bottom kill," in which mud and cement will be injected into Macondo through a relief well that engineers began drilling at the beginning of May.
If all goes perfectly, the one-two mud punch will literally be overkill. The static kill will terminate Macondo, and the bottom kill will be more like a confirmation test, akin to poking the body to make sure it's dead.
But optimism has been a dangerous attitude throughout the oil spill disaster, and the federal point man for the spill response, retired Coast Guard Adm. Thad Allen, has warned against complacency. "We should not be writing any obituary for this event," Allen said late last week.
As he delivered the latest update on the static-kill plan Sunday afternoon, he also defended the government's decision to let BP and its contractors use vast quantities of dispersants. He said that the goal of reducing the amount of dispersant used was "generally met" and that the government's field commander made decisions to allow additional dispersant on a case-by-case basis.
Although the environmental crisis has hardly passed, there is a sense these days among BP engineers and government scientists that they've got the well in a headlock. The disaster began with cascading failures and continued with cascading disappointments as attempts to kill or contain the gusher never quite worked. But since July 15 the well has been shut in, thanks to a 75-ton cap lowered onto the re-configured chimney atop the damaged blowout preventer. (See photos of the cleanup and containment efforts.)
The well has since passed an "integrity test" and, according to Allen, shows no sign of squirting oil and gas into the rock formation or up into the gulf.
The positive turn of events has led to a change in the endgame. The static kill has emerged as a potential fix that could take the pressure off the relief-well job. With hurricane season about to hit its busiest stretch, officials have feared that a tropical storm could force the rig drilling the relief well to disengage and sail away temporarily, delaying the termination of Macondo.
The static kill, which officials say could start late Monday or Tuesday, is effectively the same thing as the "top kill" attempted in late May. No one has ever been sure why the May attempt failed, but BP believes the mud simply shot out the top of the well through cracks and openings in the collapsed riser pipe.
This time should be different, and easier. The hydrocarbons aren't flowing. That simplifies everything. The mud can be injected gradually, just a couple of barrels per minute. Where the mud will go is unclear; engineers say only that it will follow the path of least resistance. The mud weighs about 13 pounds per gallon and is much heavier than the oil, so it should push -- or "bullhead" -- the oil back down the well toward its origin in the ancient rock more than 13,000 feet below the wellhead. Ideally the mud will fill the well all the way to the bottom of the well bore, where the final seven-inch pipe juts into the porous Macondo reservoir.
If it works, the pressure in the well will slowly drop to zero from its current pressure of nearly 7,000 pounds per square inch. At that point, engineers could decide to send in a large dose of cement. That would permanently plug the well at its base. BP has said Macondo will never be resurrected as a production well. (See video of the oil spill's impact on one Louisiana community.)
But there could be complicating factors. Still unknown after all these months is which avenue from the reservoir the hydrocarbons have exploited. No one is sure if the oil and gas are flowing inside the pipe or outside the casing in what is called the annulus -- the space between the pipe and the rock wall of the hole. Or the flow could be through both. Because of such uncertainties, officials plan to proceed with the relief well regardless of what happens with the static kill. The relief well is only about 4 feet laterally from Macondo, angling in gradually, with about 100 feet to go before it intercepts the annulus.
What happens in the bottom kill, and how long it takes, will depend on the circumstances of the static kill. The standard plan, outlined for months, has been to send mud through the relief well, initially into the annulus. After the mud will come cement. Then the drill string will be withdrawn and a new bit will be attached, a "mill." That would be used for the next stage: cutting into the steel casing of the well and repeating the mud-and-cement injection.
"Once we've made the intercept, depending upon the status of the well, whether we still have to kill the annulus, the casing, or both, the kill procedure could take anywhere from a number of days to a few weeks," BP Senior Vice President Kent Wells said Friday.
It's conceivable that the static kill will take care only of hydrocarbons in the central pipe and leave hydrocarbons flowing in the annulus, Allen said.
"We're not going to be satisfied until we drill into the annulus outside that pipe," he said.
The endgame is having reverberations on the shore. Some Louisiana officials are concerned that the government and BP will bail out prematurely in their response to the spill. Roughly 1,500 private "vessels of opportunity" have been enlisted to skim oil, but with the gusher clamped and oil now harder to find, there will be "resource leveling," Allen said Thursday. But he said the government has put together a plan to keep the fishermen employed at least through August.
"Obviously as we transition to a point where there is not a threat of a spill, and this is all conditioned on the fact that we will have a successful static kill and bottom kill of the well, the employment of vessels of opportunity is going to necessarily have to change," Allen said.