Kate Mackenzie What next, after the diamond saw problem?

What does the setback with the diamond saw mean for BP’s efforts to contain the oil flow in the Gulf of Mexico?

The saw was meant to make a clean cut across the top of the riser — a large pipe leading out of the blow-out preventer — that would enable a containment cap to be tightly fitted, capturing the oil and funneling it back up to the surface.

BPHowever it got stuck halfway through. The diamond saw has now been freed and BP  CNN is reporting that Admiral Thad Allen, incident commander, says  BP has ‘abandoned’ use of the diamond saw, and will instead use the giant shears (see image), which successfully severed the lower part of the riser, to make another cut above the blow-out preventer.

The shears are large and not especially precise, as the video below of the shears’ successful earlier cut demonstrates:

The implications of this are big: the shears cannot make as precise a cut as the diamond saw, which would make it more difficult to get a ‘seal’ on the leak and trap all the oil.

So the big question appears to be whether, without the precision of the diamond saw, a clean enough cut can be made to tightly fit the LMRP cap, without letting too much oil leak out.  (Check out BP’s technical video to understand what they were trying to do, and a new Oil Drum post which looks at what actually  happened).

From Bloomberg:

The setback with the blade may lead to a looser fit and a higher rate of oil leakage between the blowout preventer and cap, Allen said today at a press conference in Houma, Louisiana. BP, based in London, will decide today whether a coarser blade is required, he said.

We should note that BP itself has not ruled out either the diamond saw or sealing it to the LMRP as planned, its GoM response page merely says preparations are under way to cut the riser — without specifying which device, or what comes next.  CNN claims that the option of sealing up the cap is off the table, along with the diamond saw, and instead the company is planning to use the ‘top hat’ that it had considered a couple of weeks ago. 

However BP may have a couple of ways of making the cut clean, despite the encumbrance of the shears.

From the New York Times, quoting an anonymous technician who also says the diamond saw has been abandoned:

Because the shear will not make as clean a cut as the wire saw, modifications would have to be made to the containment cap that is to be lowered over the cut pipe. But the technician said that even with the switch to the shear and the modifications, he expected the containment cap could be in place by Thursday.

And from CNN, again:

Eric Smith, associate director of the Tulane Energy Institute in New Orleans, Louisiana, said Wednesday it may take a couple of days to put the cap in place.

“I would suspect that once they get the surface cut and the remainder of the riser moved aside, they will come in with some sort of a buffing operation to make sure that the cut’s as smooth as they can get it,” he told CNN.

BP may certainly need to be considering all options to make the fit as good as possible.

Thad Allen told a press briefing earlier on Wednesday that the next temporary option, installing a second blowout preventer on top of the existing one, was “off the table”. That suggests there are only a few short-term options left on the table right now; although BP also points out it has the “best and brightest” minds on the task, so it’s possible other ideas will emerge. However, as efforts to stop up the well near the seabed appear to have been abandoned, they seem likely to focus on various methods of containment and siphoning off the oil.

At some point however, the focus will turn to the two relief wells which, as we detailed earlier this week, could be much more complicated than simply reaching the required depth: once there, intercepting the correct point of the well can be very challenging.