Wednesday, April 2, 2008

WOW! that was close

This is a 17.5 inch Hughs Christiansen hard rock drill bit, it is the Mercedes Benz of drill bits, and it costs as much, as a nicely equipped Benz, $40,000-$60,000.

Here is the same type of bit with normal wear, all the paint is gone, the diameter of the skirts is slightly under-gauged, normal after spending several days down a hole making said hole deeper.

Here is another similar bit, although much more worn, the rocks we just went through were very tough, with lots of void space, where we couldn't maintain circulation of drilling fluids, this bit just didn’t want to go, so we changed it out, notice the extra wear on the skirts that hold the cones in place, they are slightly dished out from reworking the cuttings, this is very heavy wear on a bit.

Now, this is a Hughes diamond enhanced drill bit, it runs more around the upper end of the Mercedes Benz, say $80,000 (yes, I know Merc has some that run over $100k, but you don’t see many of those). When this thing came out of the hole everyone went OMG, we are lucky we aren’t fishing for those cones. This is the second most worn drill bit I've ever seen that still had its cones attached.

Notice the dishing from reworking the cuttings had almost eaten through the skirts and dropped the cones, normally when cones fall off, it is because the bearings have worn away and they just slip off the pin that the ride on. Here the base of the pin is almost complete eaten away.

This is actually an odd form of wear, because of drilling blind with water (blind meaning that the drilling fluid pumped down never returns to the surface). Water doesn’t carry the cuttings away as efficiently as thick drilling mud (a bentonite clay suspension with water and polymers). The annular velocity is low enough that the cuttings do not stay entrained in the flow of fluid and sit around the bit until they are reworked enough that the flow of water will haul them up the hole and out into the formation through cracks.

At the end of the day though, the drill bit worked, it got through the tough section, and made hole, so now we are running casing, of course, trying to cement it in place is going to be fun. Not.

1 comment:

Chuck said...

I'm jealous of your big bits- I'm sitting on a RAB rig for the foreseeable future starting in mid May.