Tips for Lugging a Bit or Hole Opener
Social media has changed the way people work and interact in the world. Sometimes it is a great time waster, but often it can be a great source of information. I get emails, texts and calls almost every day from people in the drilling industry who want to pick my brain about something I’ve done before.
The other night, I got into a discussion with a group of well drillers that centered around bits or hole openers backing off in broken, rough-running formations. Nobody likes to admit it, but this happens fairly often in our industry. The reasons — and cures — are pretty straightforward, but often overlooked. It is embarrassing to write on the daily report that you lost the bit, and even harder to tell the boss.
The first thing to consider is torque. The rotary shouldered connections that most of us use are torqued up to have an interference fit between the opposing tool faces. When made up properly, the metal at the face of the tool joint actually yields slightly, making a very strong joint. Most rigs have enough available torque to easily handle the drill pipe and collars. That’s what rigs are designed for. The problem arises when we have to handle a much larger tool joint. This is commonly seen on large bits and hole openers. For larger-sized bits, 6⅝ regular is a common connection. Most water well rigs can’t come close to the high torque numbers that this connection calls for. This is one of the biggest reasons for losing a bit or hole opener — improper make up torque. My friends, it is almost impossible to over torque such a bit connection with the things you have on your rig!
The fix for this has been done in different ways by many drillers for years. I have actually seen drillers weld the bit to the bit sub. This might be fine if the bit is going to last forever. But if you have to remove it, you will find that the bit and the bit sub are ruined. Not a good long-term plan. Most drillers use some sort of lug or strap system that can be cut loose and re-used. The quickest and most common way is to weld a strap vertically across the tool joint. This works in less severe formations, but in high-torque situations — since the bit probably wasn’t made up properly — the strap will shear and free the bit. Not much help there.
Over the years, we have developed a better method to lug a bit or hole opener. This is very important when using a hole opener in a pilot hole. In this case, the bit doesn’t do anything except guide the hole opener and sees very little, if any, torque. In rough running, it is easy to backlash the pipe enough to lose the bit. A proper lug system will fix this without ruining expensive tool joints.
At the top is the bit sub, and at the bottom is the bit or hole opener connection. The bit sub gets a permanently welded lug, about 1-inch-by-2-inches tall, usually made of ⅜-inch steel flat bar. It should be welded on the top, left side, and bottom, leaving the right side square, flush and unwelded. This stays on the bit sub. The lug on the bit is placed close to the top lug and extends from the bit up beside the top lug. It is only welded on the bit, not the sub.
During operation, if rough running is encountered, the joint can make up slightly without any problem. But if the bit tries to back off, the lugs will stop it. I usually leave a small gap between the lugs and measure it before I go into the hole. When I come out, I look and measure again to tell me whether the bit moved. If the gap is larger, it means the bit made up in the hole. If it is smaller, it means the bit was trying to backlash off the pipe and the lug saved it.
This technique is very important when running multiple hole openers. On larger holes, it is common to drill a pilot hole, and then come out, pick up a hole opener and ream. On large holes, it is not uncommon to see two, three or four hole openers stacked up to get to the final hole size. This means that, when reaming, none of the connections below the top one are seeing the drilling torque. That leaves them prone to back off in the hole and means they should be securely lugged. When coming out of the hole, the only lug that needs to be cut is the lower one, leaving the top one undisturbed for future use.
Hope this helps and, although I spent much of my career running fishing tools, the best approach is prevention. If I didn’t explain it well enough, or you need some advice, don’t hesitate to contact me. My advice is free and well worth it.
For more Wayne Nash columns, visit www.nationaldriller.com/wayne.