BP starts sealing Deepwater Horizon well with cement

The cementing of the bottom of the well, likely to be finished today, would bring to an end a nearly five-month battle for the oil firm.

No oil had spilled into the Gulf since a temporary cap was placed on the well in mid-July.

The explosion of the rig on 20 April 2010 had killed 11 workers and caused a massive oil spill.

The cementing operation began after a relief well finally intersected the damaged well yesterday.

BP spokesman Daren Beaudo was quoted as saying that pumping had started at 1.30 pm local time on Friday (6.30 pm Maltese time) and was expected to take "a few hours".

After the cement set, engineers expected the well to be completely sealed, he added.

BP had said earlier that when cementing had been finished, the relief well would also be plugged and sealed.

The relief well had been drilled 4 kilometres through dirt and rock beneath the sea floor.

This final cementing would mean that BP could finally leave the site and concentrate on dealing with the aftermath of the spill.

At the beginning of August, the US government had claimed that almost three-quarters of the oil spilled in the Gulf of Mexico had been “cleaned up or broken down by natural forces”.

The remaining quarter was thought to be "degrading quickly".

But more recent research noted an undersea plume of crude oil-based chemicals up to 200 metres high and 2 kilometres wide, extending 35 kilometres from the spill site.

Despite optimism about the clean up, the damage to the local economy, wildlife and the ecosystem of the Gulf is hard to fully assess yet.

On Wednesday, the US government had announced it also wanted energy firms to dismantle hundreds of unused platforms to prevent potential spillages.

Some installations had been sitting idle for decades without inspection for leaks. The new requirements were due to take effect in October.