Friday, October 9, 2009

Two Years Ago Today: Two Drill Rigs

Two years ago today, I went out early in the morning to visit two drill rigs. This is the first drill rig. They are fairly deep in the hole, but we'd like to go deeper.
The shadows were long, and although there was frost here and there, the ground wasn't frozen. Neither drill rig was inside an active mine; they were conducting brownfields exploration around the edges of an old pit.
When I arrived at the second drill rig, the sun was still low on the horizon with the frost unmelted in the shadows.
The rig had twisted off in bad ground at less than 200 feet, leaving a lot of pipe in the hole. The driller, who had been on shift with his crew since midnight, was not happy.
The front end is jacked up to level the rig on this slightly non-level drill pad.
While I was there, the driller shut the rig down prior to trying to get the twisted-off steel out of the ground. If you know how many pieces of pipe were on the truck to begin with, you can figure out how many are now in the hole.
This is some of the miscellaneous equipment and paraphernalia near the sampling side of the drill rig.

I stayed on site for most of the morning. It turned out that both rigs were going to need to move to start new holes, with neither having reached the target depth, and I had to show them the new sites and make sure the drillers were okay with the sites.


Anonymous said...

Looking at your photos, I see it was a reverse circulation could give little discussion of how it works?

Anonymous said...

Interesting post--

Yeah, I'd like to see an explanation of how this works. I work on oil/gas drilling rigs which are typically much bigger, and seem to use very different pipe--I've never seen that sort of pipe--looks like heavy-wall casing or tubing with a central tube in the middle (the rusty orange tube that looks about 2" in diameter in your photo). I assume these are strictly used for continuous diamond coring? I've never heard of a drillstring twisting off only 200 ft (60 m) down, so I guess the string is fairly delicate--or are other factors at play?

--Howard (Calgary, AB, Canada)

Silver Fox said...

Here's a general explanation, for now. The rotary bits create chips, aka cuttings, which are put in chip trays. The chips come up the inner tube to prevent sample contaminatin from the drill-hole wall. The old way didn't have an inner tube, the sample came up the outside of the pipe - that was/is called "conventional rotary drilling" rather than reverse-circulation. Nowadays, most reverse-circ drilling is done with water-fluids added to the air, rather than air alone, to minimize dust.

The drill stem was deeper in the hole than 200 feet in very broken ground. The upper part of the hole was broken ground because it was an old mine dump; the lower part was in very broken bedrock. Caving from the top caused the string to get tight, it eventually twisted off - don't remember the details of how in particular it was over-torqued or how sudden it was. Lots of pipe has been left in that particular part of the countryside, by several different drilling companies, simply because the ground is so bad. Yeah, a way bigger rig wouldn't get stuck, but it would then cost so much money that one wouldn't be able to drill as many holes as are needed to prove up an ore deposit.

Each piece of pipe on this type of rig is 20 feet in length.

Anonymous said...

Thanks for the explanation. RC drilling is totally foreign to me; I've worked on conventional rotary drilling operations for 27 years, and had no clue RC drilling even existed!


Silver Fox said...

Howard, glad I could help some. I might do a post on this sometime, though I don't really have pictures of parts of drill rigs, so it would still be kind of general. My first drilling exposure was with conventional rotary, in the late 70's, on a small rig that would maybe drill to 2000 feet if you got lucky. Reverse-circulation was new then.