Contents preface (VII) introduction 1—37
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| 4.9.5. Cable Tool Drilling
It is the earliest drilling method developed by the Chinese some 4000 years ago. A cable tool drilling equipment mainly consists of a drill bit, drill stem, drilling jars, swivel socket, and cable (Fig. 4.10). The cable tool drill bit is very heavy (about 1500 kg) and crushes all types of earth materials. The drill stem provides additional weight to the bit and its length helps in maintaining a straight vertical hole while drilling in hard rock. The length of the drill stem varies from about 2 to 10 m and its diameter from 5 to 15 cm. Its weight ranges from 50 to 1500 kg. Drilling jars consist of a pair of linked steel bars and help in loosening the tools when these stick in the hole. Under the normal tension of the drilling line, the jars are fully extended. When tools get stuck, the drilling line is slackened and then lifted upward. This causes an upward blow to the tools which are consequently released. The swivel socket (or rope socket) connects the string of tools to the cable. The wire cable (about 25 mm in diameter) which carries and rotates the drilling tool on each upstroke is called the drill line. The cable tool drilling rig mainly consists of a mast, a multiline hoist, a walking beam, and an engine. Drill cuttings are removed from the well by means of bailers having capacities of about 10 to 350 litres. A bailer is simply a pipe with a valve at the bottom and a ring at the top for attachment to the bailer line. The valve allows the cuttings to enter the bailer but prevents them from escaping. Another type of bailer is called the sand pump or suction bailer which is fitted with a plunger. An upward pull on the plunger produces a vacuum which opens the valve and sucks sand or slurried cuttings into the tubing. Most sand pumps are about 3 m long. 152 Crown sheave Shock absorber Tool guide Drilling cable Swivel socket Drill stem Operating levers Drill bit IRRIGATION AND WATER RESOURCES ENGINEERING Casing and sand line sheaves Rope socket
Drilling bits Spudding beam sheave
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