If you have drilled for any length of time, sooner or later you are going to stick your drill pipe. It’s one of the hazards of the job. Recognizing the different ways drill pipe can get stuck is the first step in prevention — and recovery.
One very common way to stick pipe is differential sticking. This happens when the hydrostatic pressure is significantly higher than the formation pressure. This often occurs when you drill through a low pressure formation that takes light mud, and then drill into a higher pressure formation deeper in the well. In order to control the high pressure formation, you increase the mud weight. This may break down the low pressure formation and force the drill pipe against the formation face in the wellbore. The pipe is then very definitely stuck. It only take 1 or 2 pounds of differential pressure over a short area to stick pipe to the point that it is beyond the strength of the pipe, or the capability of the rig. One clue to this situation is that you can usually circulate freely.
The solution is to reduce the hydrostatic pressure in the hole until it is equal to the low pressure zone that has you stuck. While circulating, slowly reduce your mud weight by dilution while holding torque on the pipe until it comes free. One problem with this method is that the lower, high pressure formation may start to flow, so be ready to start out of the hole as soon as you’re free to prevent the hole heaving around your drill pipe. You can condition the mud after you’re up in a safe zone. While tripping out under these conditions, don’t shut down for lunch, grease the rig, smoke a cigarette or anything else but keep the pipe moving. If you have to stop, rotate the pipe.
Another common cause of stuck pipe is key-seating. This happens then you drill a deviated hole. It is often caused by formation inclination — doglegging — or too much pulldown. The bit will drill a full gauge hole, but as you get deeper, the pipe will wear a keyseat in the formation. When you come out of the hole, the BHA will ride in the keyseat until the bit gets to it. Then it will stop. Clues to this type of sticky situation: you can still go down and you can circulate freely. If you have a tophead rig, you can often rotate while pulling the pipe and roll past the keyseat. If you have a conventional rotary table rig, you may have to pull into it very gently and rotate the pipe enough to drill your way out of it. This can prove time consuming and frustrating.
Unstable formations can result in a cave in. This will stick pipe tighter than Dick’s hatband. You can’t move the pipe or rotate. The solution is more serious. You will either have to jar it out or wash over it. This can be time consuming and expensive. The prevention is to keep good mud properties, and monitor your gains and losses in the pipe. At the first sign of trouble, pick up, get away from bottom and condition the hole with good mud. Once you have the pipe moving, don’t stop.
Drill pipe can also be stuck mechanically. Dropped slips or a pipe wrench can stick pipe solid. The cures are different according to circumstances. If you can circulate mud, do it. If you can move the pipe, do it. Sometimes a piece of junk will ride the top of the bit until you get up to a soft formation where you can sidewall the junk and proceed.
General rules on stuck pipe are:
- If you stick pulling up, work the pipe down.
- If you stick pipe going down, work up.
- If you can rotate, do it. This gives you some working room, rather than making the situation worse.
Remember, if you can move the pipe and circulate, you are not stuck! You might not be able to come out of the hole, but you have a chance!
A few years ago I was on a stuck pipe job in the Northern Rockies. We could circulate freely, but the pipe wouldn’t move or rotate. A classic case of differential sticking or wall-stuck, as we called it. A friend and mentor taught me a trick I’d never seen before. We conditioned the mud until the hole was as perfect as we could get it. Then we put a pretty fair amount of torque in the string and closed the blowout preventer, sealing the top of the well.
We pumped liquid nitrogen into the top of the well, and let the returns come back through the Kelly to the pits. When we had pushed the hydrostatic head of mud as deep as we felt safe, we cleared the floor and opened the preventer. Talk about spectacular! As soon as the pressure was released, the nitrogen came roaring out, lowering the pressure on the formation and freeing the pipe. We immediately started rotating, and conditioned the hole with good mud. I never had to run any tools or anything to free the pipe! I’ve only done that a couple times for various reasons. Usually, because the company man had never heard of it. But it has worked every time I tried it. My point is, every stuck pipe job is a little different, and you are going to have to think “outside the box” to be successful.
Remember, the best solution to any fishing job is prevention!