Published: Aug 02, 2010 6:55 AM EDT
Updated: Aug 04, 2010 4:30 AM EDT

NEW ORLEANS (AP) — Engineers began pumping heavy drilling mud into the blown-out Gulf of Mexico oil well Tuesday in what they think is their best chance yet to achieve the ultimate goal in a delicate process — snuffing one of the world's largest spills for good.

BP crews began the long-awaited effort dubbed the "static kill" around 3 p.m. Central time, the British oil giant said. The effort could take several days and involves pumping mud and eventually, crews hope, cement from ships to the well bore a mile below to seal off the source of the oil.

But the government and oil executives won't declare victory until crews also shove mud and cement down an 18,000-foot relief well later this month to help choke the vast undersea reservoir that feeds the well. They say that's the only way to make certain oil never escapes again.

Tests for the static kill started a couple hours earlier as crews probed the broken well bore with an oil-like liquid to determine whether there were any obstructions in the well and to assess the pressure of the bore and the pump rates it could withstand.

The test "went exactly as we could have expected," but it's too early to tell whether the static kill is successful, said BP Senior Vice President Kent Wells.

"We're so early in the process, there's no way for me to give you any early indication," Wells said, adding: "We're extremely focused on this point on making sure we execute the static kill as best we can."

Crews should know within hours whether the mud is pushing down the oil as envisioned. But engineers still won't know for more than a week whether the attempt achieved its goal because they have to wait for completion of the relief well.

"This is a really positive step forward," retired Coast Guard Adm. Thad Allen said earlier, calling it "good news in a time where that hasn't been very much good news, but it shouldn't be a cause for premature celebration."

Company officials earlier said the static kill alone — which involves slowly pumping the mud down lines running from ships a mile above — might be enough to plug up the oil, which began gushing from the sea floor after the Deepwater Horizon rig exploded and killed 11 workers.

But the only surefire way to make certain the well is permanently plugged is to fill it also with mud and cement via the relief well in a so-called "bottom kill," said Allen, the government's point man on the spill response. The relief well is set for completion as early as Aug. 11.

Crews tried something like the static kill in late May, when oil was still spewing from the failed blowout preventer, but had to abandon it because the mud couldn't counteract the flow. Engineers are more confident this time, mainly because the oil has been contained since mid-July. That means engineers can pump the mud down the well bore more slowly.

The effort is meant as insurance for the crews that have spent months fighting the spill. The only thing that had been keeping the oil from blowing into the Gulf was an experimental cap that has held for more than two weeks but was never meant to be permanent.

Allen noted that peak hurricane season is just around the corner and that a storm could disrupt progress. Tropical Storm Colin formed far out in the Atlantic on Tuesday, but early forecasts put it on a track off the East Coast rather than the Gulf.

The company began drilling a primary relief well May 2, 12 days after the Deepwater Horizon rig exploded and killed 11 workers, and a second backup well May 16. The first well is now only about 100 feet from the target.

A federal task force said Monday that about 172 million gallons of oil made it into the Gulf between April and July 15, when the temporary cap contained all the oil.

The task force said about 206 million gallons actually gushed out of the well, but a fleet of boats and other efforts were able to contain more than 33 million. The 172 million gallons is on the high end of recent estimates that anywhere from 92 million to 184 million gallons had gushed into the sea.

Judging by the latest estimate, BP could be fined up to $5.4 billion under the Clean Water Act, or as much as $21 billion if it is found to have committed gross negligence or willful misconduct.

The high-end fine would drop to around $17.6 billion if the government credits BP for the oil it has recovered, while the low-end fine would be around $4.5 billion.

Any fines would be on top of the compensation BP has agreed to pay to thousands of people harmed by the spill. Under pressure from the White House, the company set up a $20 billion escrow fund to pay all claims, including environmental damages and state and local response costs.

BP and federal officials have managed to contain large parts of the spill through skimmers, boom and chemical dispersants meant to break up the oil.

Federal regulators have come under fire from critics who say that BP was allowed to use excessive amounts of the dispersants, but government officials counter that they have helped dramatically cut the use of the chemicals since late May.

Michael Bromwich, who as director of the Bureau of Ocean Energy Management, Regulation and Enforcement is the nation's top drilling regulator, said Tuesday that the Obama administration hopes to lift a freeze on deep-water drilling before it is scheduled to expire Nov. 30.

And as businesses along the coast continued to clamor for relief from losses caused by the spill, BP said it created a special team to reduce paperwork and speed up payments to "businesspeople who are suffering."

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Contributing to this report were Associated Press writers Ramit Plushnick-Masti in Houston, Harry R. Weber on the Gulf of Mexico, and Matthew Daly in Washington.