Cordage. Two clases of lines find use in drilling operations, ordinary rope made from either sisal or manila hemp, and wire rope which is built up of many small steel wires about a hemp core or centre. In the former class, which passes under the general term of 'cordage,' the cheaper rope made from sisal is employed only for general purposes about the well, while the drilling-cables and bull ropes are of good qualities of manila hemp. Hemp rope deteriorates rapidly in very dry districts due to the fact that the hemp fibre grows only in warm and exceedingly moist climates and the moist cellular structure soon loses this moisture when brought into an arid district. It then becomes dry and brittle, loses its strength and pliability, and for this reason when not in use should be stored in as cool and moist a spot as can be found.
The individual fibers of hemp are from 6 to 10 ft. long. When manufactured into rope they are first oiled and woven into threads with a left lay, those of a lighter color and more silky texture going into the drilling cables and the more brittle, coarse and red varieties into bull-ropes. With a 2%-in. drilling cable, 31 of such threads, each composed of many fibers, make a strand ; three strands are wound with a right lay to make a rope, and three ropes, also with a right lay, compose the cable. The left lay of the fibers and the right lay of the strands and ropes, known as 'hawser' or 'cable' lay, are so made for the purpose of preventing the cable from kinking. The sizes usually employed for drilling are from 2 to 2%-in, diameter, with lengths from 1000 to 2500feet.
Manila cables for drilling are used chiefly in so-called 'dry' holes, where the nature of the ground is such that it does not cave readily and the only water in the well is that which is placed there to assist the bit in cutting the hole, and the bailer in bringing out the cuttings. `Wet' holes, which are filled with water to prevent the sides from crumbling, interfere with the motion of the cable and are usually drilled more advantageously with wire drilling-lines. The chief merits of the Manila line arise from its great stretch, or spring, through which, by giving the walking-beam the proper motion, a much heavier blow may be delivered by the drilling-tools on the end of the line. The same quality in the line causes the tools to spring back quickly when the blow has been struck, thus dislodging the bit from the cuttings that tend to stick and hold it fast.
Manila lines are used almost exclusively where drilling is carried on by means of spudding, as spudding with a wire line places too severe a strain on the derrick.
Bull ropes are made with a diameter of 2% in. and length of 90 ft. They are known as soft lay rope and consist of three strands, each strand built up of many fibers.
Wire Rope. The wire ropes in general use for drilling wells are (1) the drilling-line, wound on the bull-wheel shaft, to carry the drilling tools; (2) the casing line, wound on the calf-wheel, and used for handling casing; (3) the sand-line, which runs on the sand reel and carries the bailer in and out of the hole. The introduction of wire rope for drilling purposes is comparatively recent but its use has spread rapidly and it is now generally employed for work at depths greater than 1200 feet. Unlike much of the material employed for well drilling, these lines have practically no salvage value when they have become unfitted for further service at the well.
The line used for carrying the drilling tools encounters the most severe service of the three classes, and its cost is no small factor in drilling a deep well. These are in nearly all cases made of extra strong cast steel wire, of a grade intermediate in strength, hardness, and other characteristics between the regular cast steel ordinarily used in hoisting-ropes and the plow steel used where great abrasion is met. The construction of the line varies with the drilling conditions.
In the eastern fields, where the duty is light, the ropes are com posed of six strands of seven wires each, with a hemp centre (Fig. 53). In other fields various combinations of six strands of 12 wires, 4 strands of 5 wires, 6 by 25, 6 by 15, etc., have been .tried with varying results, mostly unfavorable, and for heavy work, the general construction has apparently settled down to the use of the standard hoisting-rope construction of 6 strands of 19 wires each, with a hemp centre of approximately the same diameter as each of the strands, or increased only enough over this to afford a proper cushion to the wire strands and prevent them from bruising or abrading each other (Fig. 54). They are put up almost invariably with a left lay, although there appears no particular reason for this, and some operators use right lay with good success.