DRILLING METHODS.
The two principal modern methods of drilling oil wells are (1) by the standard or percussion method, and .(2) by the rotary flush..., system. There are several modifications and combinations. of the two, but nearly all drilling is done by one or the other.A.---.The prin ciple of the percussion system is that of raising and dropping a heavy stem and bit on bottom, afterwards removing the drill ings, which have been mixed with water by a bailer. The rotary has been described as an auger with water connections which wash the debris from bottom by the action of a pump. ' The rotary cannot be successfully used in hard strata of lime stone, sandstone or slate, and for this reason its ust..is confined to those localities in which the principal formation incllides shales, clays and sand interspersed with occasional shells of harder ma terial. On the other hand, the standard rig does not work satisfac torily in running or heaving sand, or in heavy gas presSti-es, and is therefore used in such formation only in connection with the rotary. For any particular locality, however, one or the other systems or their combination will he found to perform the drilling,,in a capable manner.
Standard Method. When the derrick has beenerected' by the rig builders, the drilling crew of four men and their tool-dressers) take possession and prepare to start drilling or 'rig up' as it is called. It is usual to excavate a cellar 8 by 10 by 20 ft. directly under the derrick floor in order to facilitate the handling of the casing as well as to give freedom of action to the temper-screw. The cellar can be sunk by hand or, when desired, a hole frdm. 100 to 200 ft. deep is drilled and the earth thrown into it and .there re drilled and bailed out, thus providing a means of its removal. A sump is excavated by scrapers near the derrick and a dump-box in stalled under the floor for conveying the drillings from bailer to sump. The sump is often used for an oil reservoir later on when the well is producing quantities of oil and sand. A forge is placed on the right side of the derrick floor for heating the bits to draw them out to guage, while a crane (Fig. 65) with a chain hoist is so placed as to swing a bit into the forge or to suspend the bit or other equipment for connection to the drilling-tools. A lagging of manila cable is wound tightly around the band-wheel and spiked every 8 or 10 in. to prevent its being torn off. The band-wheel has been previously machined on the face, if necessary, with a turning bar. A 12-in. 6-ply stitched belt transmits power to the band-wheel from the drilling-engine, and provision is made to align the two by shifting the engine upon its foundation. The shaft of the calf-wheel is also lagged to prevent its being cut by the wire-line as well as to provide a larger diameter for the casing-line to wind upon.
The sprocket chain which turns the calf-wheel from the band wheel is put on and a clutch fitted for convenient manipulation by the driller when standing near the throttle at the headache-post.
The casing-line is passed over the four casing-sheaves on top of the derrick and threaded through the 32-in. triple casing-block (Fig.
66), from which hangs a heavy casing-hook (Fig. 67), 5 to in.
diameter. In moving casing, the links of the elevator are placed over the casing-hook, the body of the ele vator taking hold under the top coupling of the pipe. The clutch is thrown in and the pipe raised or lowered by the calf-wheel. The sand-reel lever is placed near enough to the throttle-wheel on the headache-post to permit of the driller handling both at the same time, while powerful brakes are placed on the calf and bull wheels. The sand-line is drawn on the double-drum sand-reel, the manila cable is wound on the bull wheel, after which the drilling tools are pulled into the derrick and coupled together.
A complete string of drilling tools consists (Fig. 69) of a rope-socket, jars, stem, and bit, in the order named. They are screwed together by means of a powerful jack operated on a circular track (Fig. 70), and two men are required to tighten the larger joints. The latter, which are tapered to make coupling easier and to protect threads, are made of soft annealed steel and have a shoulder about 1 in. wide which prevents, them from unscrewing when in the well. When the joints are new, they come within shouldering by hand, and should be set up by the jack and un screwed several times before put to actual use, to prevent any danger of unscrewing. They should at all times be thoroughly cleaned to remove grease or rust, and the shoulders should be free from rough or broken places. The threads often become cupped from faulty joints or excessive tightening, in which case they should be sent to the shop for re-threading. In the larger sizes of tools, the joints are 4 in. at the base, 3 in. at the top, with 7 threads to the inch, and are called 3 by 4-7 joints. They are 6 in. outside diameter, and the wrench-squares for tightening are placed close to them. Similarly 4 by 5-7, 2g. by 3g-7, 2 by 3-7, 134 by 234-8, are the sizes used, depending upon the diameter of the casing and the formation being drilled. Care should be exercised in setting up the smaller joints, as the pins are sometimes twisted off. The rope-socket for manila cable has a 272-in. hole bored through the top and tapering at the side about 12 in. below (Fig. 72) ; the end of the cable is pulled through the bore and interlaid with short pieces of manila rope. When pulled tightly into place, by weight of the tools, a wedge is formed making an effective connection. The wire-line socket (Fig.73) has a 1%-in. hole bored through to the box, with a recess above the latter ; the line is thrust through this hole from the top, the ends are turned back and pulled into the recess and hot babbitt poured in, preventing the line from pulling out of the socket.