As soon as the derrick is completed, and the en gine installed to furnish power, actual drilling op erations can be begun. The first step is the sink ing of the conductor or drive pipe through the soil to bed rock: often a wooden conductor when the rock is near the surface, but always an iron drive pipe when the surface deposits are deep. Several hundred of the first wells that were sunk in this country were drilled by the process known as "kicking down," or by the use of a "spring pole." In this process a post, driven deep in the ground outside the derrick, supported a stout tim ber bearing the tools at one end and a weight to counterbalance them at the other end. On each side of the drill were fastened loops or "stirrups." The drillers, by placing one foot in the stirrups and "kicking," or "jumping" down, made the heavy drill strike the rock, while as soon as the men lifted their feet, the counterweight would raise the drill ready for another stroke. In the spring pole method an elastic pole securely fas tened at one end was used instead of the balanced timber. Both of these methods were employed ex tensively in the Pennsylvania fields, but they were essentially a poor man's makeshift. They were effective only in shallow wells, and were quickly discarded when the superiority of deep borings was recognized.
At the present time there are two main systems of drilling, depending on the form of apparatus used: the American and the Canadian, or, as they are more commonly called, the rope or cable sys tem, and the rod system.
The drilling tools in the American system are suspended by means of a hemp rope wire cable, which passes through a pulley wheel or block at the top of the derrick. The "string of tools," as it is usually called, is divided into two parts, the lower part giving the downward or cut ting stroke, and the upper part giving an upward stroke to loosen the drill from the rock. Between these two parts come the "jars," one of the most important adjuncts of successful drilling. The jars resemble two long flat links of a chain sliding back and forth on each other with perfect ease. The lower part of the string of tools consists of the drill, or bit, the auger stem into which it fas tens, and the lower half of the jars. The upper part of the string includes the other half of the jars, the sinker bar, and the rope socket. The dif ferent tools vary widely in size and weight, but. for ordinary deep drilling, the whole string will measure somewhere about 60 feet long, and weigh from 1,800 to 2,200 pounds. The auger stem and the bit usually make up more than half the total weight. If the weight of the lower half of the jars is included, it appears that approximately two thirds of the weight of the whole string is in the lower part.
During the process of drilling, the string of tools is connected by the cable to a walking beam, oper ated by a small engine. At each movement of the
beam, the tools rise and fall with a regular monot onous clank. On the downward stroke, the upper half of the jars slide part way down into the lower half, but as the walking beam rises, the slack is taken up, and the jars are quickly drawn out to their full length, delivering a sharp upward blow which serves to loosen the drill. The impact of the heavy drill, falling forty or more times a min ute, and constantly turned by the drillman, pul verizes the rock into sand, the rate of drilling vary ing from a few feet to possibly a hundred feet a day, according to the nature of the rock. The proc ess of drilling appears simple enough in principle, but in actual operation the regulation of the stroke to take the greatest advantage of the blow requires much skill on the part of the drillman, whose sole guide is the "feel" of the tools as he regulates their movement.
Besides the tools actually used in cutting the hole through the rock, the usual drilling equipment includes a great variety of accessory implements to be used in special cases: reamers to enlarge the bore holes; sand pumps and bailers to remove the powdered rock, water, and oil ; and elaborate "fish ing" tools to be used in case of accidents. These fishing implements especially occupy a prominent position in the drillers' equipment, since at any time a broken cable or string of tools may put an end to further work unless the well can be cleared.
By means of one or another of the fishing tools it is possible, at depths much over 1,000 feet, and in a hole nowhere over a foot in diameter, to cut off a broken cable, unscrew a string of tools, and raise the parts one by one, or even to cut a new thread on the end of a broken tool, so that a socket can be screwed on it again. Frequently weeks are spent in patiently fishing for a lost string, when, without accidents, the entire well could be completed easily in less than a month.
The process of drilling, aside from occasional accidents, consists essentially in keeping the ma chinery going twenty-four hours a day. The drill ing crews work in shifts of twelve hours each, each shift including a drillman and one or more tool dressers to assist him. At varying intervals, the tools are drawn out in order to replace the bit with a sharper one, this drawing out and returning the tools to the drill hole being the process where the derrick with the pulley at its top is necessary. While the bits are being changed, a sand pump, which is really only a tube with a valve in the bot tom, is sent down to clean out the accumulation of pulverized rock in the drill hole. This cable sys tem of drilling is best suited to deep wells, and has been adopted extensively in Russia, Burma, and in most other places where it has been necessary to exceed a depth of 1,000 feet.