Retired Coast Guard Adm. Thad Allen, the government's point man for the spill response, told reporters Friday that engineers must remove the cap so they can raise the failed blowout preventer. The blowout preventer is considered a key piece of evidence in determining what caused the April rig explosion that unleashed the gushing oil.
The leak was first contained when engineers were able to place a cap atop the well. Workers then pumped mud and cement in through the top in a so-called "static kill" operation that significantly reduced pressure inside the well. Officials don't expect oil to leak into the sea again when the cap is removed, but Allen has ordered BP to be ready to collect any leaking crude just in case.
The Department of Justice and other federal investigators are overseeing the work to remove the blowout preventer, Allen said. The device - which was designed to prevent such a catastrophe - will be taken out of the water with the well pipe still inside to ensure the pipe doesn't break apart any more than it already has.
Keeping the blowout preventer intact is important because it's considered an essential piece of evidence in determining what caused the blast aboard the Deepwater Horizon on April 20. After the blast, 206 million gallons of oil spilled into the Gulf of Mexico until the temporary cap stopped the flow.
The goal is to drill the final 50 feet of a relief well beginning Sept. 7, Allen said. From there, it will take about four days for drilling crews to reach their target. The relief well has been called the ultimate solution to plugging the well.
Once the relief well is drilled, engineers will be able to pump mud and cement in through the bottom of the well, plugging it once and for all.
Meanwhile, the U.S. government said Friday that it is reopening more federal waters in the Gulf of Mexico for commercial and recreational fishing that had been closed because of the spill. The government is reopening 4,281 square miles of waters off the coast of western Louisiana.
Oil sheen has not been seen there since July 29, and scientists found no oil or dispersants on samples of the area's shrimp and finfish.
Twenty percent of federal waters in the Gulf remain closed.
"We're sort of nibbling at the edges if you will, areas that have been free of oil for the longest time and were oiled the least," Lubchenco said.