When the top of the bit leans to one side of the hole so that the fishing-tools cannot be passed over it, the task becomes more difficult, as it must be brought to a vertical position by drilling around it either with a spud (Fig. 186) or with a hollow reamer (Fig. 187). These bring it to the centre of the hole and at the same time they scrape in cavings from the side which hold it in place. Of the two tools, the hollow reamer, which is really a double-spud, is much the more effective, as its two prongs spring out to a wide sweep when they have passed below the casing shoe, and if the top of the lost tool has not become too deeply imbedded in the formation alongside it they work it back to the centre of the hole.
If these attempts fail, it may be found possible to drill a hole with the drilling-tools off to the side and below the lost tool, into which with a little maneuvering it may be made to fall and then be in a position to be grasped. Another tool used for bringing a lost bit to the centre is the wall-hook, consisting of a long bar bent to a semicircle at the bottom and given a wide sweep so that when run in on tubing or a manila cable it swings the top of the lost tool back to the centre.
When all the attempts outlined above have failed, the plan of shooting the bit off into the neighboring formation is tried. Either liquid nitro-glycerine or 60% dynamite in sticks is inserted in the hole in a sheet-metal tube run into the hole on the end of the sand-line. The tube is made the same length as the bit in order that the force of the shot will apply equally at all points and not drive one end into the formation and leave the other end protruding into the hole. Instead of one electric detonating-cap several are used, to insure an explosion, and the sand-line, with an insulated wire fastened to it at intervals of 50 or 75 ft., completes the electric circuit. Before the shot is fired the casing is pulled up to from 50 to 100 ft. from bottom.
A simple, but more dangerous, method is that of firing with a fuse. The dynamite is inserted in the hole in a water-tight tube on the end of the sand-line. The fuse is lit at the surface and the charge promptly lowered ; and while this method is usually suc cessful, especially with shallow holes that allow ample time for the charge to reach the bottom, yet occasionally a premature explosion occurs. The inevitable result is a wreck of the casing opposite the point of explosion, and the hazard is not warranted if the electrical appliances for the first method can be obtained.
Among other fishing-tools employed for recovering lost tools is the `jar-knocker' (Fig. 188), devised for loosening drilling tools that are being run without jars, usually with a manila cable, and have become imbedded at the bottom of the hole so that a pull with the drilling-cable does not release them. It is from 8 to 24 ft. long and is run into the hole on the end of the sand line, with its lower portion around the drilling-cable. As heavy a pull is taken on the cable as it will safely stand and the jar knocker is dropped onto the rope-socket of the tools a number of times from a distance of 20 or 30 ft., by raising and lowering the sand-line. The jar of this contact, in conjunction with the strain on the cable, soon loosens the tools. The jar-knocker is
also used for loosening the two ends of a set of jars that have become locked and do not move freely.
A feature in connection with the prob lems of loosening either tools or casing that are lodged tightly in the hole is the fact that the jar applied through the mo tion of the walking-beam is not as great as might be imagined from observing the sweep of the beam. This is due to the stretch in the line between it and the fish ing-tools. For this reason, any method by which a strain may be placed on the tools or casing to be loosened, as the one just illustrated of pulling the drilling-line taut and then jarring with a separate tool, is more likely to be productive of results than is the simple jarring alone.
This principle, of the application of both a pull and a jar, is employed in the casing-bowl method for dislodging tools, wherein the tools are grasped first by a bowl and set of inside slips (Fig. 189), run into the hole on the end of a string of casing (Fig. 190). The casing is held at the surface by a spider and slips, sup ported by either hydraulic or screw-jacks, and the spider and pipe arc raised by the jacks (Fig. 191) until the strain on the casing is as great as may safely be ap plied without danger of parting the pipe. A socket and string of fishing-tools is then run down inside the pipe until the neck of the rope-socket on the lost tools is grasped, and jarring is then com menced. As the tools gradually become loosened by the upward jarring, the pipe and bowl are raised by the jacks so as to maintain a pulling strain on the lost tools, thus gaining the full effective value of the jarring until the tools are entirely free and may be pulled out. An adapta tion of this method is shown in Fig. 192. A shoe or bowl with a beveled inside surface, is first run in on the end of the casing: A slip-socket is then lowered until it grasps the lost tool, and the casing raised until the beveled surface meets the bottom of the socket, thus applying both the pull of the casing and the jar of the walking-beam to the socket. . The horn-sQcket TFig. 193) is a tool with a taper opening for going over a lost tool and taking a friction-hold by which it is held while being pulled out. It is used chiefly for small tools that are quite loose in the hole, such as bits, working-barrels in pumping-wells, and under-reamer lugs that have broken or become lost from the reamer. The latter are particularly elusive pieces of metal, their shape and small size rendering their capture diffi cult and their hardness making it almost impossible to drill them up. At times they may be pushed off into the side of ' the hole, but the movement of casing usually dislodges them and they drop back to the bottom again. A basket similar to that shown in Fig. 194 may occasionally be made to catch a lost lug, by running it in on the drilling-tools and churning until the wickers have closed in about it. A great variety of special tools of one kind and another has been devised for recovering these lugs, but as yet nothing that may be considered thoroughly satisfactory has been developed.