‘There could be something in the wellbore that can be problematic’

Has Thad Allen, incident commander for the Gulf oil spill, reassured those fearing a deeper rupture in the well casing?

The worry, of course, about a leak or rupture deep in the wellbore itself is that it could make the leak more difficult to fix.

Senator Bill Nelson and representative Dennis Kucinich – (both Democrats, but at almost opposite ends of the party’s political spectrum) have both raised the prospect of a well casing problem that makes the well leak ‘unfixable’.

Many blogs posting about the possibility of a well casing problem have pointed to a Wall Street Journal report saying that BP said its ‘top kill’ attempt “may have failed due to a malfunctioning disk inside the well about 1,000 feet below the ocean floor”.  An anonymous Oil Drum commenter wrote a much-linked-to piece arguing that a ‘disk’ wouldn’t appear at such a depth, therefore the report most likely pointed to a problem in the wellbore.

True, the WSJ story also said that “people familiar with the operation” said “much of the drilling mud may also have escaped from the well into the rock formation outside the wellbore.”

How much to read into all of this? We’ve seen some truly great stuff on The Oil Drum, but an anonymous comment is what it is. And some of that great stuff has included other good explanations of why top kill was going to be difficult right from the start, even without well casing problems.

Nevertheless, the possibility can’t be ruled out, according to Thad Allen. At a press conference on Monday, he said discussions involving interior secretary Ken Salazar, and energy secretary Chu before top kill began raised the prospect of problems in the well casing.

This, he said, lead to BP “erring on the side of safety” on how much pressure they would exert during top kill.

Allen added that this risk was also guiding the procedures being undertaken now:

So I’m not going to use any hard and fast scientific evidence or anything like that.  I think there’s a general notion by everybody that there could be something in the wellbore that can be problematic.  We don’t know because there’s no way to really check it.  That’s the reason they ceased the top kill procedure where it was at and went to containment, and then relying now on the bottom killer, going into the bottom of the well near the reservoir to put the mud in and seal it from there.

When the mud goes in the wellbore, it will go up and down and fill it, and when it does that it’ll—if there’s any problem with the wellbore and the casings, it will just be mud going out into the formation or the strata and not oil.  One of the reasons we’re venting the oil out of the containment cap right now is we don’t want to put too much pressure down in the well just in case there is a problem with the wellbore.

But it’s a generalized concern.  I think everybody’s known it for a fair amount of time.  It’s something just to be taken account when we’re laying out the plans.

Was that responsive?

Q:  Is there any concern that you could have oil coming out of the formation if your—if your casing is compromised?

ADMIRAL ALLEN:  I guess there could be, but I don’t think there’s any indication of that right now.  That’s the reason they’re trying to produce all the oil that’s coming up through the riser pipe and venting the rest of it off.  And that’s the reason they decided not to just put a cap on with another blowout preventer after the top kill was not effective, and I don’t think they knew to a virtual certainty what the condition of the wellbore was.  They just did not want to take that chance.

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