Directional drilling is more complex than one would initially assume, not only because of the very harshe environment but also because of the challenges found in steering a drill at the end of a few miles of drill pipe. Definitely on of those things where the closer one looks tha harder the task becomes.
Thanks for the clarification, but there are still a few missing details. But that does sound like a really harsh environment. Almsot as harsh as the temperature monitor on a steel ladle. But the ladle is not at the bottom of a few miles of pipe. And the drilling mud that I have come across had the consistency of 3/4 cured cement, only sticky. It may be softer at 350 degrees, though.
I recall seeing a model of this I beleive in the Houston Museum of Natural Sciences.
Mud motors spun by drilling mud used to be used. The mud is pumped continuously to remove rock chips from the drill and the mud is weighted (density adjusted) to balance the geological pressure in the formation. Correct, the pipe string used to be stationary for directional drilling. Directional information was transmitted to the surface by pulsing the mud or by wire.
Newer systems called Rotary steerable systems change direction of the cut by changing the configuration of e either the pads on the sides of the drill bit or the point of the drill bit continuously as the bit rotates to change directions.
Apparently tools that adjust the drill configuration to bend the bit point continuously as the drill turns have a fixed segment at the end of the string that doesn't rotate that that serves as a reference for the drill point orientation.
Wikipedia article on "rotary steerable system" notes that inclinometers (pendulum) and small gyroscopes and compases were mounted in the motors to sense the angle and direction of the bit.
Dlmz, the concept of utilizing pulse delay triangulation is interesting, but it would have a bit of uncertainty because the ground is not homogenious, meaning that the velocity of a shock wave through the ground may vary quite a bit in the different directions from a well head. But it is a concept that may have enough value to be worth a bit of thought, if nothing else. And right now I am wondering how they keep a drill head pointed in any particular direction at the bottom of the rotating drill pipe. Or is that the case of the hydraulicly driven drill head and the pipe does not turn? I think that I am aware of that technology existing.
I wasn't as clear as I should have been. The first two techniques I mentioned in the first sentence, gps or sonic triangulation were things I had speculated about, prior to asking folk in the industry. These are not used as I understand it. It is the simpler angle of the bit variations at each length of the drill pipe string as the pipe string is lowered into the hole dead reconnning that is routinely used to compute the bit position. Someone actually in the industry may wish to comment on experimental techniques or current variation.
I was especially intrigued on how these systems deviate from textbook performance behavior at these extreme conditions. I would imagine that there is a critical demand for seasoned, experienced engineers who have empirical experience in these areas (which would help create a long-lasting career in this field of knowledge).
Dlmz, thanks for the explanation. And the navigation method sounds just like "dead reconning", which I have used in the distant past, long before GPS was available, or even existed. And that makes sense that a swashplate type of steering would be used, the question being about how those shock pulses transmitted actually work. But I know that they have been steering well drilling for many years, so they must be able to get adequate results. The triangulation does make sense, although it is hard to imagine that it would be very accurate. But evidently it is.
I am not expert. But I have posed this question before, too. I was thinking 3d private GPS,transmitted shock pulses triangulated from the surface. Please correct me if this information is less than accurate. I only mention to get the discussion started. My understanding is that the bit is "steered" with a swash plate back of the bit motor. Hydrolically or electrically controlled to tilt the bit a little bit up down right left, the bit blindly chews forwards in the direction of the tilt. To know where it is is a matter of keeping track of the tilt angle and the length advanced and map out each increment of advance and its direction. Knowing where it is is then a matter of plotting "integrating" each of the incremental angles and advances as the string descends from its known starting position in the hole. The temperatures run about 360 - 410 F as I understand it down at typical texas well depths and increases with depth. Imagine running your electronics in the kitchen oven and adding some heat of motors and power dissipation. The early electronics used old germanium transistors and simple 4 bit controllers since they were more heat tolerant, I understand for years and years after they were obsolete topside. I am not in the business, directly. The above is more heresay party conversation living in Houston, near oilpatch. One Christmas party street conversation began, I found a 65 million year old fossil today, floating exposed in a streambed in an oil field outside Ft. Worth. I looked it up on wiki. The studied reply I received without blinking was, umm, no, 70 - 72 million. My wife is a plaleontologist with ... :) .
It is certainly correct that the downhole environment is about the most hostile environment that we can imagine. It would certainly be interesting to have some correct explanation about the mechanism of steering a well direction at those depths, as I have never heard or seen any discussion of how it is actually done.
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