‘Killing’ BP’s Macondo Oil Well Takes Mud, Precision Pressure

'Killing' BP's Macondo oil well takes mud
Thad Allen, the U.S. National Incident Commander, has said that plugging the Macondo well might take two to five days after the relief well is drilled. Photographer: Andrew Harrer/Bloomberg

BP Plc is likely to intercept its Gulf of Mexico gusher this month, ahead of schedule, kicking off a “kill” process that may take as little as two days or drag out because of complications caused by the well’s depth.

To stop the worst oil spill in U.S. history, BP is drilling a relief well, from which it will be able to cut into the Macondo well, 5,000 feet (1,524 meters) below the ocean’s surface. Once the interception is complete, London-based BP will pump mud to temporarily plug the leaking well, until it can apply a cement seal.

BP expects to kill the Macondo well by the middle of next month, spokesman Robert Wine said in a telephone interview yesterday from Houston.

“It’s a very complicated process,” Wine said. “The fact that we were ahead of schedule with the main length of the well is good, gives us a bit of extra time to take things steadily and safely.”

BP shares have dropped 49 percent since the April 20 blowout that sank the Deepwater Horizon rig, killing 11 workers. The stock rose 3.5 percent in London trading yesterday to 333.3 pence.

Thad Allen, the U.S. National Incident Commander, has said that plugging the Macondo well might take two to five days after the relief well is drilled. Fighting the force of the natural gas coming up through the well, contending with pressure created by the depth of the water, and potentially struggling with an inadequate containment system may cause the timeline to drag, according to engineers and analysts tracking BP’s progress.

Electromagnetic Tests

“If it was shallow water, it wouldn’t be anything serious,” said Don Van Nieuwenhuise, director of Petroleum Geoscience Programs at the University of Houston. In deep water, the mud will flow out if unchecked. “They have plenty of extra mud, but if you have it flowing out of control, it wouldn’t take too long to run out of it.”

BP already has 44,000 barrels of mud on hand for the operation, Kent Wells, the company’s senior vice president of exploration and production, said last week in a technical briefing.

BP’s first relief well has reached a depth of 17,725 feet, the company said in a statement yesterday. BP conducted seven electromagnetic tests to detect the steel casing of the Macondo well, known as ranging tests, Wine said. These tests take about a half-day to perform, and ensure that the well is on track.

A Better Seal

In mid-July, BP hopes to replace the cap that is currently funneling the flow from the Macondo well to containment vessels. The new cap has a larger capacity and will sit atop the blowout preventer, and may form a better seal than the current cap, said David Pursell, a managing director with Tudor, Pickering, Holt & Co. in Houston.

Should BP successfully secure the new cap, it will improve the company’s chances of successfully filling the well with mud from the relief well, Pursell said. Without it, BP would run a risk of the mud flowing directly out of the hole, Pursell said.

Once in place, the cap will let BP fill from the top, if needed, to reinforce the mud, Van Nieuwenhuise said.

“It’s not necessary to do the relief well, but it can help,” Toby Odone, a spokesman for BP, said from Houston.

The cap will help BP contend with the particularly strong upward force created by the vast natural gas reservoir that feeds the Macondo well, Pursell said. The new seal may be able to restrict the amount of leaking mud, creating back-pressure that will more successfully contain the gas, he said.

Heavy Mud

The Macondo well produces about 100 million cubic feet of natural gas a day. “That’s a big well, anywhere in the world,” Pursell said. Natural gas in a well can provide the same effect that gas in a bottle of soda does, forcing liquid -- in this case oil -- out of the top at a higher speed.

The strength of the gas could push the mud up and out of the well, he said.

To prevent the mud from rushing out of the well, BP will try to find a mud that is heavy enough to outweigh the pressure of gas coming out of the well, said Les Ply, a Houston-based geologist who has participated in kill operations in the past.

An appropriate balance must be struck -- if the mud is too heavy, the rocks around the reservoir can be cracked or overburdened, he said. “Mud will take the path of least resistance. You want the path to be up the well bore,” he said.

Finding the right pressure and mud weight can be challenging for killing a well at this depth, because there’s an additional pressure dynamic created by the 5,000 feet of water bearing down on it, said Van Nieuwenhuise.

“It’s water, so it won’t patch itself,” he said. The goal will be to slow the mud flow enough to plug the well adequately so that cement can be poured in and set, Van Nieuwenhuise said.

Even with these potential complications, confidence in the relief well’s success is high, with U.S. National Incident Commander Allen calling it a “proven” technique.

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