Fig. 207 illustrates a simple but remarkably useful tool for grasping the outside of crooked and odd-shaped pieces of pipe. It is made from the body of an ordi nary combination-socket, with the spring and slips removed, and slotted near the so that a 'dog' of any desired size or shape may swing on a pin-hinge placed in a recess on the outside Fig. 208. DOGS FOR TUBING-SOCKET edge. The 'dog,' or 'dogs,' if provision is made for two to swing opposite each other, is free to move exactly as does the flapper-bottom of a flat-bottom bailer, and when in a horizontal position it rests on a shoulder turned near the bottom. When the impression-block has indicated the size and shape of the projection to be grasped, a suitable dog is made (Fig. 208), so shaped that when the socket is lowered over the lost pipe the dog swings upward. Then when the socket is raised, the dog grips the pipe with a friction-hold while it is being withdrawn.
Another tool occasionally used is a bowl with a long, tapered, inside thread, similar to that in a die-nipple, by which it is made to screw over and cling to the lost tubing. The cutting-thread,' and thread of the pipe on which the tool is run, are made left-hand, so that if the lost string is wedged tightly the bowl not only grasps the top piece but also unscrews such a portion of the tubing as will turn.
The most common accident to sucker-rods, in pumping-wells, is that of unscrewing at the joint of a pin and box. They usually may be screwed together again without having to pull them from the well. When the string is parted by a rod breaking, the lost portion is recovered either sucker-rod socket or with a 'mouse trap.' Both tools are run inside the tubing on the rods ; the former (Fig. 209) is constructed like the combination-socket used for fishing lost tools, and is the more effective of the two unless the top of the rods has become burred so that the slips will not pass over it. The mouse-trap (Fig. 210) is made from a piece of heavy pipe, small enough in di ameter to go inside the tubing. In its simplest form it has a fork shaped hinge near the bottom, which falls in around the pipe underneath the sucker-rod box and holds it while the rods are pulled out. Another form contains a slip by which a friction-hold may be secured at any point on a rod.
Rotary Fishing Tools. When drilling is being carried on by the rotary method the variety of accidents that may happen is smaller than when cable tools are used, since the drill-stem and bit are the only equipment run into the hole. Such difficulties as occur with these are generally of minor consequence, •but when troubles do develop they appear to lead, more often than with cable-tool wells, to the abandonment of the hole. If the job
reaches such a stage that the fishing-tools are run in and out of the hole frequently, the work progresses much more slowly than with cable-tool wells, where the tools are run on a line.
• The most common difficulty results from the twisting and separating of the drill-stem, usually near the bottom where the torsional strain is greatest. 'Twist-offs' are recovered either by spears that grasp the inside of the pipe with slips, or with various styles of bvershots that run over it and grip it on the outside, usually directly underneath a collar. The usual type of spear (Fig. 211) has openings through which the circulating fluid is pumped as with the rotary bit, and has a single circular slip that grasps the full body of the drill-pipe on the inside. A short diamond-shaped guide is inserted in the bottom for steering the spear into the pipe, but if the top of the pipe has fallen off to the side of the hole, considerable patience is often required before the spear may be made to go into it. In such a case an off-set joint is usually placed in the drill-pipe on which the spear is run, directly above the spear, so that it is swung off to the side of the hole and passes more readily into the lost pipe.
The overshot most commonly used is made with a set of springs on the inside (Fig. 212) which permit the tool to pass down over the lost pipe, but which, when pulled up, clasp it underneath a collar. Another form is that shown in Fig. 213. This contains three or four 'dogs' on a pin-hinge, which swing up when going down over the couplings of the loSt pipe and fall back to a horizontal position when beneath a coupling so that, when lifted, they pull it up. A third style (Fig. 214) is shown recovering lost pipe in Fig. 215. In this the two slips are heavy solid pieces, supported on a shoulder in the body of the overshot. They are so made that when placed together their lower edge is a complete circle, while the top edge is not circular but has the inside diam eter of the bowl for one axis and the outside diameter of the lost pipe for the other. As the bowl is lowered over a collar of the lost pipe, the tops of the slips are pushed back, but fall in against the pipe as soon as the collar is passed, and when the bowl is raised, the portions represented by the small axis lodge against the pipe beneath the col lar and bear up against it while it is being pulled up. A shoe with an opening cut in one side, as shown, is usually run ahead of the bowl for guiding the lost pipe up inside of it.