When the casing resists the usual attempts with a spear to free it, the plan illustrated in Fig. 197 is often found successful. As in the casing-bowl method of loosening tools by the aid of an auxiliary string of pipe, the casing-spear is run into the hole on the end of a second string of casing, that will pass readily inside of the frozen string. The spear is attached to the pipe by a 'casing sub,' which has an outside thread for screwing into a coupling of the pipe on which it is run ; its lower portion is a box for fastening it to the casing-spear and the upper end is a mandrel, similar in shape to the neck of a rope-socket. When the spear has been lowered to the point where the cavings are binding the casing, it is made to take hold of the casing and as great a pull is taken on the auxiliary string of pipe, with a set of jacks, as is safe. A socket and string of fishing-tools are then run down on the drilling-line, inside the second string of pipe, the mandrel of the casing-sub is seized and jarring is commenced. A second set of jacks may be used to pull directly on the frozen string of casing, and this with the pull of the pipe on the spear and the jarring applied with the tools and socket combine to place a terrific force on the frozen casing. If this fails, either to loosen the pipe or to part it, some new line of attack must be followed.
At this point several methods of procedure may be followed, depending largely on local conditions. The simplest is the abandonment of the frozen casing and the insertion of a smaller sized string. But circumstances may be such that it is con sidered imperative that the pipe of the size frozen be carried to a greater depth than it had attained at the time it was lost. It then becomes necessary to part the frozen casing at a point above the zone where it is bound tightly, pull out the recovered portion and run it back with a new casing-shoe on the bottom, and drill a new hole off to the side of the portion left remaining in the hole.
In the course of the attempts to loosen it the pipe may have parted, but if it has not done so it may be divided at any point by cutting or dynamiting. Before doing this it is cus tomary to ascertain the point nearest the surface where the binding effect of the caved material ceases. This is learned through the fact that when the spear is jarred at a point op posite where the pipe is bound, the top of the casing at the surface will not move or exhibit any 'vibration' when the hand is placed on it. But when the jarring is applied at a point in the pipe above the cavings, a noticeable movement of the casing is apparent at each stroke of the walking-beam.
Casing is cut by means of a tool (Fig. 198) holding four small sharp-edged wheels similar to those used in an ordinary hand pipe-cutter. The cutting wheels are each held in a sliding block, all the blocks pointing towards the centre of the body of the tool. It is run into the hole on tubing and when the desired depth is reached, a long taper mandrel is lowered inside the tubing on the sand-line. This mandrel enters an opening in the body of the cutting-tool and pushes out the blocks holding the cutter wheels (Fig. 199). The tubing is then turned and the
mandrel gradually forces the cutter wheels out into the body of the casing. Another type of cutter (Fig. 200) is so constructed that the taper mandrel is part of the tool and when it has been lowered on tubing to the point at which the casing is to be cut, a short reverse turn of the tubing releases the mandrel, which then pushes out the cutter-wheel blocks as it is raised by a pull on the tubing. When this cutter is used, the tubing is sus pended from the temper-screw by which it is pulled up at the same time that it is being turned.
Sometimes considerable difficulty is encountered in endeavor ing to cut casing, and, to expedite matters, it may be decided to shoot it. The general methods outlined in the discussion of side tracking lost bits are employed for tearing the casing apart, or the shell containing the dynamite may be lowered on the end of a string of tubing, screwed up tightly so that it allows no water leakages, and exploded by dropping down on it, through the tubing, a short piece of pipe containing two or three sticks of dynamite with caps and fuses. Whenever possible, however, it is advisable not to use any but the electric method for detonat ing, as the liability of a premature explosion with other methods involves risks of injury to the men and damage to the casing.
A third method of parting pipe is that of ripping it until it is so weakened that it may be pulled apart. The chief use of the tool shown in Fig. 201 is for perforating casing to admit oil, as shown by the series of sketches, but it serves equally well as a ripper when used with a suitable knife. The body contains a slotted opening for the passage of a bar up and down beneath a knife, which swings on a pin. Screwed into the lower end of the bar is a long rod or plunger, serving as a guide for a frame with two or more expanding wings of spring-steel that bear against the inside of the casing. When lowered in the hole, on tubing with a set of jars between the tubing and the perforator, this frame is placed above a small spring-key, situated near the lower end of the plunger, and the frame is pushed ahead of the body of the perforator while it is being lowered. When the proper depth has been reached and the tools and perforator are pulled up a few feet, the bar and plunger are drawn up by the body of the perforator, leaving the expanding wings motionless until the frame has slipped down over the spring-key. The key and nut at the end of the plunger now prevent the frame from further movement on the plunger, and when the tubing and perforator are again lowered, the springs bearing against the side of the casing hold the frame quiet and the bar at the upper end of the plunger pushes up the loose end of the knife. The point first pierces the pipe and as the body of the perforator is lowered further, the knife comes to a horizontal position, punching a rectangular hole and holding the tools and tubing from further movement down ward by the square shoulder on its lower side which will not cut down through the pipe. The tools are then raised to the point at which another hole is to be cut and the operation repeated.