“Let Me Tell Ya”: Thinking About Well Casing
January 4, 2013
Although I have been talking about well casing and drop pipe in several recent columns, I did wander off with some thoughts about conventions of the past last time. I hope you did get to the NGWA Expo in Las Vegas and had a happy and safe holiday season. Here’s wishing a great 2013 to all you readers.
I have talked about different types of couplings for T and C well casing in the past. One type I did not talk about, and frankly never used, was so called drive pipe. I understand the couplings on this pipe were tapped in such a manner that the threaded ends of the pipe itself butted together inside the coupling. Using a regular tapered coupling, even if the pipe was really tightened up, there would still be a gap between the ends-however small-inside the coupling. I understand that drive pipe was designed to eliminate this and give a nearly smooth surface inside the casing.
I also understand and have been told by drillers that used this type of pipe that it was impossible to keep joints tight if any hard driving was done on the casing. Here I am going on what I have heard and can’t really report any experience that I’ve had. I have to say it sounds like a great concept, but perhaps in practicality didn’t work. I would be pleased to hear from any readers who have used drive pipe, and what their experiences have been.
Another practice that I never used and think is somewhat unusual, but I have seen, is the welding of threaded couplings on galvanized casing. The drillers who did this told me that they had experienced coupling failure in really hard driving-that is they drove the coupling right down over the threads. I can see where welding the coupling in addition to tightening it up good and snug would give one a stronger joint, but I don’t think it did much for the galvanizing as a chain is no stronger than its weakest length. I couldn’t really call that a true galvanized casing. I know some fellows who only welded one side of the casing-this at their shop-and then just tightened the joints with chain tongs out on the job, as they did not have a portable welder. As in many things in well drilling, if it worked for them then more power to them.
Speaking of hard driving brings to mind the use of a drive head. I know some drillers who just drove right on the coupling with the drive blocks of their tool string. Most drillers, however, use some sort of drive head. Several types of these heads are shown in the tool catalogs-the most popular being the kind that threads in the upper coupling, the other being one that merely drops in that coupling. The drop type of head drives against the top of the coupling but does provide a buffer against any battering that would result from driving right on the coupling as mentioned above. The threaded type is designed for harder driving, but has the disadvantage of having to be threaded and unthreaded at least partially every time the tool string was put in or pulled out of the casing.
Actually, for light driving, not using a drive head and just banging against the top of the coupling isn’t that bad. Heavy driving is a different matter. For many years I used a short pipe nipple with just a regular coupling threaded on top of it as a drive head. After a lot of driving the nipple would fracture and I would replace it and go back to driving. While not as good as a commercial drive head, this system allowed me to pull the tools without taking this so-called head off-much like a drop type head. Of course, if you are using welded or plain end casing, a drive head is essential or you will batter the end of the casing, making welding very difficult.
In any type of drilling where driving is necessary, it is essential to use a drive shoe. This product is attached to the very bottom of the casing, either by welding or screwing on. The drive shoe is, in effect, half of a coupling with a really heavy walled “other half” that contacts the earth or whatever we would be drilling through. The whole assembly is heat treated and where, for instance, a 4-inch casing would have a wall thickness of just under -inch, the bottom edge of the shoe would have a wall thickness of more than a -inch. Cable tool shoes also are tapered to a rather fine edge at the extreme outside diameter. When a lot of steel casing was still being used in rotary holes, a so called rotary shoe was used. In this model, the end was tapered to look a little like an arrowhead so as not to gouge the drill hole wall. As most rotary drilled wells in Michigan are now cased with PVC, I haven’t seen a rotary-style shoe in a long time.
In the years right after World War II, material was pretty hard to get and the driller had to use what was available rather than what he really needed. Sometimes, my father was unable to purchase drive shoes and so he just threaded a coupling on the bottom of the first length of casing to stiffen it. I can remember in several cases this stiffening was not enough, and we collapsed the coupling and the bottom of the first section of casing and had to pull it out and start over-always an un-fun thing to do. The days of the late 1940s saw the use of some really unusual or strange products, and this included well casing. I have seen wells with 31⁄2-inch ID casing, 41⁄2-inch ID casing, and other unusual sizes for southern Michigan. Heck, as I wrote earlier, my dad and I even used quite a bit of 21⁄2-inch casing. All these I would consider goofy sizes, however some of you fellows in other parts of the country may find our 2-inch, 3-inch, 4-inch, 5-inch and 6-inch sizes equally goofy.
Another topic for another time is the affect of casing size on well capacity. I will keep that one for the future, and it may raise more questions than answers.
In my monthly weather report, we have had a very fine fall here in Michigan with a little rain now and then and very mild temperatures-really great working weather. This column is written just before Thanksgiving and I was in town earlier today wearing just a shirt and was quite comfortable. However, as sure as the sun sets in the west I know that snow and real cold are coming. All the best to you, our readers. Work hard, work safe and enjoy our profession. It is one of the more vital ones to mankind. ND
Attendees check out a booth at the National Ground Water Association’s annual Expo in Las Vegas, in December. Photo credit: Jeremy Verdusco.