Oil Well Drilling Primer

Discussion in 'General Discussion' started by Minuteman, Jan 27, 2007.

  1. Minuteman

    Minuteman Chaplain Moderator Founding Member

    There are three ways to turn a drill bit. The "old" way is to turn the "kelly" via the rotary table thus turning the entire drill string with bit on bottom.

    2nd way is newer technology which has a "top drive" unit that is mounted just under the traveling blocks in the derrick and runs up and down on a track. It screws into the drill string there (on Top) and is hydraulically spun. So you can drill a 90' stand of drill pipe at a time instead of a single 30' joint.

    The way to drill directional and horizontal, which is what they are doing in the Marcellus and other natural gas plays, is to use a "mud motor". It is a heavy walled pipe that has a rotor on the inside. The last couple of feet has a section that is free turning. The force of the "mud" or drilling fluid passing through the rotor turns the bit. So the only part of the drill string that turns is the last couple of feet of the mud motor.

    Mud motors have a "bent sub" that bends the motor a few degrees off center. Once your bend is established the bit will continue in that direction and "build" angle the deeper you go. You can build up to a 90 degree angle and then straighten it out and drill horizontally. A monitoring sytem called MWD (measurement while drilling) gives you a constant read out of tool face orientation and azimuth. So if your tool face, the direction your drilling in, starts to "walk" out then you turn the drill string a little bit to re-adjust the tool face back to your orientation.

    Directional companies claim that if you could bury a coke can 10,000' deep any direction within a mile from the well they could drill down and hit it.

    This technology is what makes drilling so much less of an enviromental impact than it used to be. You can drill dozens of wells going off in different directions from the same well pad. So one well site, one road into it and dozens of wells.

    Also a new practice is starting to get popular. Multi-Lateral drilling. Drill a vertical hole down to the pay zone. Kick off horizontal and drill into the pay zone several thousnad feet. Then pull back and kick off in the opposite direction and drill horizontal several thousand feet in that direction. I have seen as many as 4 laterals off of one vertical bore.

    Most pay zones are only a few hundred feet thick and many are less than a hundred. So in conventional vertical wells you drill down through the pay zone and expose maybe 200' of oil or gas bearing formation. The oil and gas seeps from the exposed formation into the vertical bore hole and is brought to the surface.
    Now imagine drilling into that same 200' thick pay zone and then "kicking out" orizontal and exposing several thousand feet of formation. You can see the advatages to the horizontal technology.

    I don't know if I clarified or confused.
  2. ghrit

    ghrit Bad company Administrator Founding Member

    Pretty good explanation except for how they kick the mud motor to change direction. Maybe preset on the surface? Academic interest only.

    Around here, the thinking points to up to 6 horizontal laterals from one bore (or one pad, I'm not sure yet.) There are indications that they not only turn horizontal, but then make a turn on the horizontal and wind up with a series of parallel laterals in pay rock. "The talk" is roughly 5000 vertical (depends on overburden, of course) and maybe 2500 horizontal. The MWD remains mysterious to me, but I saw something the other day that points to sonic centering in the pay strata.

    The environmentalists are hemorrhaging over frac water disposal, and the river basin commissions are sweating the withdrawals from the Susquehanna and Delaware Rivers.

    The top drives are interesting. The track has to be pretty stout to take a sock full of torque. Pics that have been posted don't show it well. Now I know what to look for, I'll look closer. All the rigs in the area appear to be guyed rather than free standing.
  3. Minuteman

    Minuteman Chaplain Moderator Founding Member

    Most of the motors I have worked with you have to pull it back to the surface, break the connection, change the bend, then tighten the connection and run it back in the hole. But now they have a new tool that is adjustable downhole without pulling it. I don't know exactly how it works. Something with the presure of the drill fluid.

    Here are some good links to explain top drives, mud motors, and MWD. As for MWD we have a couple of computer nerds that come out with it and it's all greek to me. If you cant put a pipe wrench on it it's beyond my pay grade.


    http://www.tescocorp.com/data/1/rec_docs/503_20150e - Top Drive 350 EXI 600 Web.pdf


    Measurement while drilling - Wikipedia, the free encyclopedia@@AMEPARAM@@/wiki/File:Question_book-new.svg" class="image"><img alt="Question book-new.svg" src="http://upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png"@@AMEPARAM@@en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png


    A mud motor and a small top drive unit
    BTW, the rig in this thread doesn't have a TD it is a conventional kelly rig
    picture2. td_rigclose.
  4. ghrit

    ghrit Bad company Administrator Founding Member

    Read them, I did. Helpful. Thanks.
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