STANDARD CABLE-TOOL SYSTEM The principle of the cable tool or percussion system is the action of a bit, a heavy mass of sharpened steel, upon the rocks in such a way that impact will cut and crush them. The crushed material is then removed by bailing.
"Drilling Dry" and "Wet."—Where it is necessary to put only enough water into the drill hole to keep the cuttings soft and protect the bit against overheating, the hole is said to be "drilled dry." Where the hole is kept full of water during drill ing it is said to be "drilled wet." A "dry hole" in oil-field parlance is a test that has failed to strike oil. The test may have encountered a flow of water but if no oil were encountered the hole is said to be "dry." A " wet " hole is a hole full of water during drilling and has no relation to whether or not oil has been found.
String of Tools.—A string of standard cable tools (see Fig. 7, page 47) consists of the rope socket, sinker bar, jars, auger or drill stem, and the bit. The cable is attached to the tools by means of the rope socket.
This cable is first'wound on a spool called the bull-wheel shaft and then led over the crownsheave on the top of the derrick and then down to the floor. A special connection called the rope socket joins the drilling tools and the drilling line. The sinker bar is placed between the rope socket and the jars.
The drilling jars have a stroke of 12 to 16 in. They are used in drilling to give play for light up strokes to loosen the bit if it sticks while drilling clay or shales, or becomes frozen by drill cuttings collecting around the tools.
The auger or drill stem is placed between the jars and the bit. The stem gives driving force to the bit. It varies in length from 18 to 36 ft. An average stem is 28 ft. long.
In raising or lowering the tools from the hole it is necessary to connect the bull wheels with the driving machinery. This is accomplished by means of a bull rope (or two ropes on deep wells). The bull rope is a soft manilla cable 2% in. in diameter which runs from the bull wheels to the band wheel, which in turn is driven by a 90-ft. belt that extends from the drive pulley on a steam engine, gas engine or electric motor. This furnishes the means of raising the drilling tools from the hole.
Drill Bits.—The bit, is of course, the most important part of the drilling tools. There are several types of bits. (See Fig. 8, page 48.) The cutting edges only are tempered. The face of the bit on the cutting end is hollowed somewhat like a horse's hoof. The cutting edges of the ordinary bit of the Cali
fornia or of the Mother Hubbard pattern are flared out beyond the body of the bit. The flare of the bit wears until the bit tends to bind. The bit is then withdrawn from the hole and sharpened. The hollows in the bit are watercourses which allow the cuttings and mud to pass around the bit, and water to i freely follow the cutting surface.
Rope clamps (see Fig. 7, page 47) extend below the temper screw and hold the drilling cable fast while I drilling is in progress. The wear and tear of the drilling cable on the clamps wears them out rapidly so that new clamps are re quired every four or five wells that are drilled. To overcome the expense of throwing the clamps away, liners for the clamps were tried with the result that several new styles of clamps with liners are now in use and all of them save clamp expense.
Tool Joints.—The special joints used for connecting the dif ferent parts of the string of tools, such as bit, auger, stem, jars, and rope socket, are called tool joints. These joints consist of male and female parts, or pin and box. The pin is solid and tapered. (See Fig. 7, page 47.) The box is also tapered. The joints are described by giving the diameter of the end of the pin, the base of the pin, its length, thus: a 3 by 4 by 7 joint means 3 in. at the smallest diameter, 4 in. at the base, and 7 in. long.
Tool joints are also used on rotary-drill pipe, but the pin and the box in this case have a hole bored through them, so water can flow through the drill pipe freely and maintain circulation.
Wrenches.—In putting a string of drilling tools together, heavy wrenches are used. These wrenches weigh from 150 to 300 lb. each, dependent on their size. They come in pairs, one right-hand grip and the other left-hand. (See Fig. 9.) They are usually hung or balanced in the derrick, so that they can be swung on the tools without heavy lifting. Leverage on these heavy wrenches is obtained by a circle and jack. (See Fig. 9, page 49.) This jack works on the rack and pinion plan. The circle is a track with pinions. The jack is operated by a lever called a "forgie" stick. The procedure is to tighten the tools by hand as far as possible, and then use the jack and circle to finish the tightening. Casing is "set up" by using casing-tongs. (See Plate II, page 51) These are manipulated by hand or by machinery, dependent on the amount of tightening desired.