To ensure the ruptured well is permanently sealed, BP will also proceed with its plans for a relief well that will intersect the damaged well and could be used to pump more heavy drilling mud and cement in from below.
'Extra level of safety'
BP managed to stem the flow of oil into the ocean two weeks ago, but the tight-fitting cap placed over the well was never supposed to be permanent solution.
"The only thing that separates the oil from the sea now is the valve. This puts thousands of feet of mud and cement in between," Eric Smith, the associate director of the Tulane Energy Institute, said.
"The idea is to have as many barriers as possible between the ocean and the reservoir. We're adding an extra level of safety."
Al Jazeera's Gabriel Elizondo, reporting from New Orleans, said this was a delicate and rather lengthy procedure.
"What this basically entails is pumping mud into the well head, which is a delicate operation because the well head is highly pressurised.
"If this works, they then have the option of putting some cement into the well head that should seal it.
Our correspondent said: "They will know if this first step of the operation works within the next 24 to 48 hours. If it does work, then BP will need to wait 5 to 7 days before they pump more mud into the well head and seal it from the bottom.
"Officials say that if both these steps work, then sealing this well head permanently could be completed in next week or so."
A permanent seal to the well will end the months-long technical nightmare for BP that began on April 20 with an explosion on a rig 80km off the Louisiana coast.
Millions of litres of crude spewed into the ocean after the blast, which killed 11 workers and ruptured the well a mile beneath the surface of the sea.
But even when the well is finally capped, the environmental disaster will be far from over and the political and financial implications will be felt for some time to come.
|The 'static kill' operation involves injecting drilling mud into the well and concrete to seal the leak
Gulf fishing communities and business owners are still counting the cost of the worst offshore oil spill in US history after it forced the closure of large swaths of rich fishing grounds and dealt a severe blow to local tourism.
BP, which leased the Deepwater Horizon rig, has sought to reassure residents it will continue to restore the area once the plug is in place.
"There's still a lot to do," Doug Suttles, BP's chief operating officer, told reporters on Sunday. "I know people are worried about that, will we pack up and go, and the answer is clearly 'No, we're not going to do that'."
BP managed to put a tight-fitting cap on the well two weeks ago, and that has temporarily stopped the flow of oil into the ocean.
The oil giant's response to the spill sparked widespread public anger in the US and last week the company announced that Tony Hayward, its chief executive, was stepping down.