How deep drilling(oil, etc) avoids drill twisting on its axis? Wouldn’t kilometers long steel drills be akin to licorice?
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The pipe is quite strong in that axis. There will still be some amount of twisting but no permanent deforming. It just means that you need to spin the pipe a few times before the head starts spinning at the bottom of the well. The pipe is selected to be strong enough to withstand these forces.
the actual drill head is only at the bottom, the rest is just pipes that flush away the dirt and carry mechanical movement
The drill pipe twists slightly with resistance from the drilling, but it’s been engineered to allow for enough force before getting permanently deformed, it doesn’t really matter how long the pipe is, the force in each section is actually the same if you consider friction ***with the well walls*** negligible
One big thing is that the fluid recirculating through the well both lubricates, cools, and takes material back up from the drill head. It’s called drilling mud, and it’s a highly engineered thing.
Imagine stretching an elastic band or a spring until it breaks.
Now imagine stretching a chain of two until they break – you have to pull further, but you have to pull just as hard.
A very long drill isn’t any weaker, so it’s no more likely to yield or break than a short one, it will just bend/stretch further than a short one – as long as the rotation force gets to the cutting bit at the bottom, it’s doing its job.
The multiple pipes connected to the drill bit flex at the joints. They have drills that they can guide and go down and sideways
They don’t. The pipe absolutely does twist on its axis. On a very long pipe you might put 10 or more rotations into the top before the bit starts to turn at the bottom. But that’s OK. As long as the bit is turning and you don’t yield (overstress) the pipe it’s fine.
There is a *huge* weight at the bottom, right behind the bit, made of thick wall pipe called “drill collars”. These make sure the pipe is all in tension so it doesn’t want to buckle. One of the major jobs of the driller is to make sure the weight-on-bit is right so that the pipe *doesn’t* buckle. You always want the drill string to be “hanging” from the rig. The weight in the bit should only be from the drill collars.
All these rotations are part of why you need such tight joints…if the bit sticks the pipe will temporarily wind up. When the bit releases all that twist unwinds, quickly, and can overshoot and actually unscrew a connector if you didn’t have the joint torques correct in the first place.
The drill string does twist on its axis. The drill string is akin to licorice. Good analogy and obviously it can withstand a little more torque than licorice.
When you stop drilling on the surface, the drill keeps turning on bottom until the licorice unwinds.
Certain drilling applications also utilize a piece of downhole equipment called a mud motor. This is essentially a helical rotor inside a tubular. The tool sits at the bottom of the drill string below the collars. Drilling fluid or mud is pumped down the drill string and through the mud motor; the pressure of the drilling fluid spins the rotor inside thus creating concentric power to spin the drill bit. They are not used in all drilling applications but rather mainly for hard rock formations and directional drilling applications wherein the driller and MWD (measure while drillng) hands will “steer” the drillstring into the zone they want it. These tools are most often used in conjunction with PDC type drillbits. Check out this Wikipedia article. https://en.m.wikipedia.org/wiki/Mud_motor
Edit: spelling
The ability of the drill to resist twisting is enhanced by its geometry: a hollow pipe. The same amount of steel formed into a solid rod would be much less stiff (more strain per unit stress), and the difference between the stress in the center (zero) and the stress in the perimeter of a solid rod is much greater than the variation in stress of the pipe.
Differential stress will result in failure of the material if the stress is high enough to reach a plasticity point. A rod that’s stressed to the point of plastic deformation will snap because the outer portion is twisted and undergoes plastic deformation, while the center is not. For a pipe, even if you were to stress the pipe to the point of plastic deformation, so long as there’s sufficient weight on the pipe to keep it from collapsing, you’ll still have a pipe, as the stress on the inner portion and the outer portion of the pipe is nearly equal – you’d have a slightly twisted pipe.
Does the entire string spin, or do they pump mud down the pipe until the last x feet, and that part is a spinnable turbine that spins just the drill bit.
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