Oil giant BP this week announced it had permanently sealed the well at the centre of the Gulf of Mexico oil spill, following two concreting operations.
On 19 September BP completed a “bottom kill” operation to pump drilling mud and cement down through a relief well to create a permanent seal in the 40mm wide annulus – the ring-shaped cavity between the well casing and the rock formation – of the original borehole.
In an earlier “static kill” operation completed on 5 August drilling mud and cement were pumped down through the original borehole to create a seal inside its 180mm diameter casing.
The bottom kill was completed via a relief well which penetrated the original well’s annulus at a depth of 5.5km – around 244m above the oil reservoir.
Progress had been hampered when relief well drilling had to be suspended during Tropical Storm Bonnie in July.
Drilling also slowed when the relief well approached the planned intersection point with the original well.
At 6m intervals closer to the meeting point, the drill pipe had to be withdrawn slightly while a flexible wire was inserted inside. This emitted an electrical signal to pick up the magnetic field from the original well bore to determine its proximity.
“We haven’t even thought about what we’re going to do this field some day”
Doug Suttles, BP
“For that reason, about the last 305m became much slower in terms of progress than the drilling to date,” said US Coast Guard national incident commander Thad Allen.
The relief well intercepted the original on 16 September. “Bottoms up circulation” was then conducted to return the contents of the annulus to the rig for evaluation, to determine whether hydrocarbons or cement were present at the intersect point.
This was found not to be the case, so annulus cementing could proceed as planned.
BP will now complete the abandonment of the original well, known as MC252, and the two relief wells by removing portions of the casing and setting cement plugs.
It will also now begin the process of dismantling and recovering containment equipment and decontaminating vessels that were in position above the well site.
BP chief operating officer for exploration and production Doug Suttles said there are substantial oil and gas reserves still in the reservoir, but BP has no plans
for the future exploitation of these resources.
“We haven’t even thought about what we’re going to do with this reservoir and this field some day,” he said.
BP was also drilling a second relief well but a spokesman said this was no longer needed and would be abandoned.