A swage can be used to remove dents made by boulders or to drive out collapsed portions. This work may be only of a temporary nature and should the pipe collapse a second time, as often happens, the swage again may be called into use and the pipe kept in fairly good condition until landed. In driving the shoe through a tight hole or tough stratum of clay, the shoe often becomes pinched or oblongated. In such a case the bit may be used to detach the lower portion and drive it to bottom where it can be drilled up—in fact 8 of 10 ft. is sometimes drilled off the bottom of a string a section or two at a time and disposed of in this way. When a string of stove-pipe cannot be forced by hard driving, it is usually aban doned and the next smaller size of casing run to bottom, for stove pipe is much more difficult to handle than screw casing for the reason that it cannot be readily pulled back. One string is generally used in California, the average depth of landing in the deeper territory being about 750 ft. There are single 16-in. columns, however, over 1000 ft. lOng, the object being to shut out all sand-strata. The pipe is cut off flush after landing with the casing-sills in the cellar, in order not to interfere later on with the screw-pipe.
For convenience in handling all screw casing, a large iron ring called a 'spider' is placed at the cellar bottom. The spider has two projecting lugs for its support. The casing is run through a beveled hole and can be suspended at any depth by inserting four curved steel slips (Figs. 96 and 97) having serrated edges which act as wedges between the body of the spider and casing. The advantage of being able to lower the latter only a few inches at a time is often helpful in shutting out a caving formation, allowing the tools to work on bottom without interruption. Several makes of elevators are used, the Wilson (Fig. 100), Fair-Mannington (Fig. 98), Scott (Fig. 99), and Fisher being generally employed. The Wilson is easily manipu lated, a door on the side opening wide enough to admit the casing instead of being hinged at the back as in the Fair, while the Fisher is especially reliable for extreme tension. With one exception elevators are made upon practically the same principle, that of two links by which the casing is raised, the body having a hinge at the side or back, to allow of its being placed around the casing. A device known as the latch holds the body together when in use. The Union single-link elevator (Fig. 101) possesses advantages in handling the larger sizes of casing. It has no hinge, but grasps the pipe by the insertion of two bushings (Fig. 102), after the body of the elevator been lowered below the coupling.
The casing-shoe is placed upon a joint and tightened until it butts with the latter upon the shoulder, after which, hot babbitt is poured into the recess between the sleeve of the shoe and the pipe. This is clone to prevent the shoe from unscrewing as well as to strengthen it. Casing is inserted one length after the other until bottom is reached, care being taken to see that the threads are properly lubricated and the joints screwed straight. Each is started and screwed by hand after which a jerk-line is run to the crank shaft, and the engine used to securely tighten the coupling, both at the 'mill' end and the 'well' end of the latter. Heavy pipe tongs are required for this work and are counterweighted at the swinging end so that no help is required to pull them back for a fresh hold. Casing 12%-in. diameter is generally used inside a string of 16-in. stove-pipe and is carried as far as possible, the average string in California being about 1500 ft. in deep-well drilling. After being landed, the 12-in. casing can be cut off 50 or 60 ft. up inside the 16-in. stove-pipe, effecting a saving in pipe.
An adapter (Fig. 103), which acts as a guide for the 10-in. is placed upon the top of the cut portion of the 1272-in. to permit the smaller size pipe being lowered without dan ger of hanging up. If the 10-in., when landed, has not been used to shut out water, it can also be cut a few feet from the shoe of the 127i-in. The water-string, however, should extend to the surface, where it is sus pended on landing-clamps which are placed under the top collar. A short string called a 'liner' can be used to run into the oil-sand, thus effecting a saving in pipe.
The blue shale in one locality may be firm and cause no trouble, while the blue shale in an adjoining district may cause considerable trouble because of its caving and unstable character. It is therefore impossible to fore see or to judge conditions until they are actually met, and for this reason no set rule obtains for the handling of ,pipe or the drilling of wells.
As before stated, the tools work more satisfactorily when 10 to 25 ft. below the shoe, the bit having more latitude for cutting a maximum hole. The casing should be kept loo enough, however, to prevent the rope socket from going below it, for should the drilling-line part, a difficult fishing job may be caused when the tools have a chance to lean against the wall of the hole instead of stand ing upright in the casing. When under-reaming, casing should be at least 5 or 6 ft. above where the under-reamer is working, to pre vent its striking the shoe. It is not always necessary to under-ream shale, but the hole through clay and all hard formations should be enlarged to permit free passage of all debris which might otherwise wedge in be tween the collar and the wall and stick the casing. Where boulders occur, the use of the under-reamer is advisable to pull them into the hole where they can be drilled up and a source of danger to the casing be eliminated. The formation in many oil fields is sharply inclined, and the tools must be held up or 'tight-hitched' to prevent following the dip of the strata and getting a crooked hole. To correct the latter, hard material such as cast iron, rock, etc., is thrown into• the well and the hole plugged back to a vertical line, when drilling ahead is resumed. This often has to be repeated many times before a straight hole is obtained. Tight-hitching applies to practically all oil-well drilling, for there is liability of the hole going crooked at any time when the tools are allowed to run loose. Under the latter condition, there is also danger of twisting the drilling-line off, sticking the tools, or digging a flat hole when the bit is not free to turn. If the formation be caving, the casing should be alternately lowered and raised sufficiently often to insure its being entirely free. If the mud falls in against it, or, in oil fields phraseology, "The casing becomes logy," is should be pulled back far enough to free when the mud, which falls in, can be cleaned out. Brown shale usually makes good drilling and does not cave badly, while blue clay when once drilled usually gives no further trouble. Boulders may freeze or mash the casing. If not too the dented portion may be swaged out, but if it be the water-string, the pipe should be with drawn, the damaged portion removed and the string replaced. Water sand is generally severe on screw-casing, and, in passing through it, freezing may be expected. In drilling sand out of the casing, the sand often packs so hard that there is some danger of splitting the joints, driving the bit through the pipe. Sand can often be held in check by dropping quantities of clay in the hole and mudding the walls, thus protecting the pipe from freezing as well as from the heaving sand.