Sunday, August 12, 2007

Borehole Inspection

Well, I've finally used my first borehole camera for the purpoose for which it was originally designed: pipe inspection. We had reason to suspect the integrity of the GISP2 casing, both because instruments had snagged in the casing in the past, and also because GPS measurements of the height of the casing indicated that the top of the casing was sinking faster than we would expect, if the casing was locked-in to the firn at its base.

So this season I brought a second camera system, based on an old downhole camera and winch, with the intention of looking at the casing from the inside. Yesterday I put the camera in the borehole to see what we could see.

It wasn't very long before we ran into the first irregularities:

This looks like what you might expect if the casing is getting compressed along its axis; the joints in the casing are flare joints, and the piece of casing going into the flare gets fractured and forced into the pipe.

A closer view of the same.

After making the decision to move past this damaged section of casing, I came to the next damaged section:

This on isn't as bad as the first, but will probably get worse over time.

Then the third:

And then I found a strange thing- what I think must be a piece of fiber from the fiberglass tube, dangling down the hole:

And beyond that, more compressional damage:

Not long after this point, the battery in the camera died, so I had to return to the surface. I have a second battery pack, which seems to last longer. Perhaps I'll go down again with the better battery, and see if I can make it all the way down to the fluid! I did that this afternoon at the DISC borehole, drilled 2 seasons ago for testing purposes.


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