ROBERT, La. — BP started pumping heavy mud into the leaking Gulf of Mexico well Wednesday and said everything was going as planned in the company's boldest attempt yet to plug the gusher that has spewed millions of gallons of oil over the last five weeks.
BP hoped the mud could overpower the steady stream of oil, but chief executive Tony Hayward said it would be at least 24 hours before officials know whether the attempt worked. The company wants to eventually inject cement into the well to seal it.
"I'm sure many of you have been watching the plume," Hayward said of the live video stream of the leak. "All I can say is it is unlikely to give us any real indication of what is going on. Either increases or decreases are not an indicator of either success or failure at this time."
The live video stream Wednesday showed pictures of the blowout preventer and oil gushing out. At other times, the feed showed mud spewing out, but BP said this was not cause for alarm.
A 30,000 horsepower engine on a ship floating above the well was pressure-pouring heavy liquids known in the oil business as "drilling mud" or "kill mud" down through drill pipes and hoses attached to the five-story-high blowout preventer sitting on top of the well. Once the liquids have forced the oil back, the well can be cemented and shut off.
A weak spot in the blowout preventer could give way under the pressure, causing a brand new leak. But engineers and geologists following the effort said the likelihood of success grew with each passing hour.
The ultimate success or failure of the top kill effort may be known by midday today — perhaps about the time President Barack Obama is scheduled to discuss new restrictions on offshore drilling at a news conference after receiving a report on drilling safety from Interior Secretary Ken Salazar.
Obama is expected to extend the informal moratorium that he declared after the BP spill began on new offshore drilling permits in the gulf and off the North Slope of Alaska until the cause of the accident is determined and stricter safety and environmental safeguards are in place.
Obama will also repeat his call to Congress to change the law that currently requires the Interior Department to act within 30 days on all applications for drilling permits offshore and on public lands. Obama and Salazar have argued that the requirement does not provide adequate time to assess the hazards of proposed oil and gas operations.
Some fishermen who have been hired by BP to clean up the spill say they have become ill after working long hours near waters fouled with oil and dispersant, reporting severe headaches, dizziness, nausea and difficulty breathing.
Rep. Charlie Melancon, D-La., wrote to Health and Human Services Secretary Kathleen Sebelius asking fort the agency's help providing medical treatment. Melancon said he expected BP to pay for the clinics.
Meanwhile, dozens of witness statements obtained by the Associated Press show that a combination of mistakes, equipment failures and a deference to the chain of command impeded the system that should have stopped the gusher before it became an environmental disaster.
Company executives and top drill hands argued for hours about how to proceed before a BP official made the decision to remove heavy drilling fluid from the well and replace it with lighter weight seawater that was unable to prevent gas from surging to the surface and exploding.
One employee was so mad, the rig's chief mechanic Doug Brown testified, that he warned they'd be relying on the rig's blowout preventer.
"He pretty much grumbled, 'Well, I guess that's what we have those pinchers for,' " Brown said of Jimmy Harrell, the top Transocean official on the rig. "Pinchers" was likely a reference to the shear rams in the blowout preventers, the final means of stopping an explosion.
Brown said in sworn testimony on Wednesday that the BP official stood up during the meeting and said, "This is how it's going to be."
Also, days before the explosion, BP officials chose, partly for financial reasons, to use a type of casing that the company knew was the riskier of two options, according to a BP document.
If the cement around the casing pipe did not seal properly, gases could leak all the way to the wellhead, where a single seal would serve as a barrier.
Workers from the rig and company officials have said that hours before the explosion that killed 11, gases were leaking through the cement, which had been set in place by contractor Halliburton. Investigators have said these leaks were the likely cause of the explosion.
In a handwritten statement, Transocean rig worker Truitt Crawford said: "I overheard upper management talking saying that BP was taking shortcuts by displacing the well with saltwater instead of mud without sealing the well with cement plugs, this is why it blew out."
BP declined to comment on his statement.
Information from the New York Times, the Associated Press, the Los Angeles Times and McClatchy Newspapers was used in this report.