![]() The thrust mechanism on most top-head rigs is a pair of roller chains consisting of two chain sections. ![]() The pulldown chains on modem drill rigs are powered by a hydraulic motor, which provides better thrust control. On older rigs, the sprockets under the rotary table are powered mechanically through a PTO and clutch. The chains are attached to the kelly swivel and extended over sprockets at the top of the mast and under the rotary table. Generally, two roller chains apply the thrust for rotary tables. This mechanism is called a pulldown or feed drive. Rotary rigs are equipped with a mechanism to apply a downward thrust to the drill string. Most top-head drives are powered by hydraulic motors capable of variable speeds rather than positive constant rotation. Top-head-drive drill rigs do not use a kelly bar. The top-head mechanism moves down along the rig mast as the boring is advanced and is raised to the top of the mast to add a length of drill pipe. Torque is applied at the top of the drill string. The rotary table normally is a mechanical, positive drive mechanism. By removing the kelly bar, you can add drill pipe and work the pipe through the open hole in the rotary table. The drive kelly bar slides through the rotary table while rotating. The drill string may be square, hexagonal, or round with grooves or flukes on the outside wall. The kelly, which is attached to the mud swivel, is the uppermost section of the drill string that passes through the rotary table. The rotary table is a rotating platform that transmits torque to the drill rod through the kelly. Military drilling machines use rotary table drives. Torque is applied to the drill string, which rotates by using three basic designs-rotary table, top head, and quill-and-drive bar. Many drill rigs may use both mechanical and hydraulic drives. Power is delivered to the various components through hydraulic pumps and motors or through mechanical transmissions and clutches and geared on roller-chain drives. Drilling rigs are truck- or trailer-mounted and are powered by an on-board engine or by a PTO from the truck transmission. The drill pipe is the link transmitting torque from the rig to the bit, and the pipe carries the drilling fluid down the hole.Ī. Drill pipes or rods are joined to a bit to form the drill string. Rotary drilling is sometimes called mud rotary drilling. ( Table 5-1 shows the relative performance of drilling methods in various geologic formations.) Drill cuttings rise to the ground surface in the drilling fluid. A bit is rotated against the formation while mud is pumped down the drill pipe, through ports in the bit, and back to the ground surface through the annulus between the drill pipe and the borehole wall. ![]() A rotary drill rig has three functions: rotating the drill string, hoisting the drill string, and circulating the drilling fluid. Rotary drilling with mud is the most widely used method for water-well construction. Well Drilling Chapter 5 Well-Drilling Methodsĥ-1. ![]()
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