Rotating equipment includes the devices that make the bit turn. On a conventional rig, the equipment consists of a swivel, an upper kelly cock, a special length of pipe called the kelly, a lower kelly cock, a kelly saver sub, the rotary table, the drill pipe, the drill collars, and the bit . Some contractors install a special system on their rigs called a top drive. It replaces many parts of the conventional rotating system; top drives are discussed in more detail later.
According to the American Petroleum Institute (API), all the pipe between the swivel and the bit, including the kelly, the drill pipe, and drill collars, is the drill stem. (The API is a trade association that sets oilfield standards and specifications.) The drill stringincludes only the drill pipe—not the kelly and the drill collars. Be aware, however, that practically everybody in the oil patch uses "drill string" to mean the drill pipe and the drill collars.
Fig. 7 Schematic of rotary system
ITis a remarkable device. IT sustains the weight of the drill stem, permits it to rotate, and provides a passageway for drilling mud to get into the drill stem. IT also has a large bail, similar to the bail, or handle, on a bucket but much, much larger. IT’sbail fits inside the hook at the bottom of the traveling block. Crew members also attach the rotary, or kelly, hose to ITs side at the gooseneck. The gooseneck is a curved piece of erosion-resistant pipe. Drilling mud enters ITthrough the rotary hose and the gooseneck.
IT is squareor hexagonal, instead of round, because the flat sides provide a way to make ITturn. The driller lowers ITinside a corresponding square or hexagonal openng in the kelly bushing. The kelly bushing fits into another rotating component called the master bushing. The master bushing fits inside the rotary table. Thus, as the rotary table rotates, the master bushing and the kelly bushing also rotate. Since the IT mates with the kelly bushing, ITalso rotates. The pipe rotates because the crew connects it to the ITsbottom. Finally, the drill collars and the bit rotate because the crew connects them to the drill pipe.
IT passes through the kelly bushing. The master bushing rotates the kelly bushing, which rotates IT. The drill pipe, drill collars, and bit rotate as well. They disappear into the rotary table where you can't see them. At the same time, the mud pump sends mud through the rotary hose and into the swivel. From the swivel, the mud flows inside and down the kelly, the drill pipe, the drill collars, and out the bit. The mud shoots out the bit and lifts cuttings up the hole to the surface.
The crew fits the master bushing into IT. During normal drilling operations, the master bushing drives the kelly bushing. When drilling stops and the kelly bushing is out of the master bushing, the master bushing can hold the slips.. Slips have strong, toothlike gripping elements called dies.Slips fit around the drill string and suspend it in the hole. With the drill string suspended by the slips, the crew can remove the kelly and the swivel from the drill string. The traveling block and hook no longer suspend the drill string.
IThangs from the traveling block's hook in place of a conventional swivel. A powerful heavy-duty motor in IT turns a threaded drive shaft. The crew stabs, or inserts, the unit's drive shaft directly into the top of the drill stem. When the driller starts ITs motor, it rotates the drill stem and the bit. The rig therefore does not use a conventional swivel, a kelly, a rotating rotary table and master bushing, or a kelly bushing. Rigs with IT still need, however, a rotary table and master bushing to provide a place for the slips to suspend the pipe.
IT consists of the drill pipe and special, heavy-walled pipe called drill collars. Manufacturers make ITfrom steel, but they also use aluminum.
ITis heavier than drill pipe, however. The drilling crew uses them to put weight on the bit to make it drill. They install them in the drill string below the drill pipe. Number of drill collars depends on how much weight the bit needs and on how much the drill collars weigh.
ITis a threaded piece on each end of the pipe . The pipe maker welds IT to the pipe. The crew connects the pipe with IT. IT adds a significant amount of weight to drill pipe, but not enough to make it weigh anywhere near as much as drill collars.
Manufacturers make two types of IT for rotary drilling: roller cone and diamond. Roller cone have steel cone-shaped devices that roll, or turn, as the bit rotates. Most of them have three cones; some have two and some have four, however. Its makers mill or forge teeth out of the body of the cones, or they insert very hard tungsten carbide buttons into the cones. The teeth or inserted buttons cut, scrape, or gouge the rock as IT rotates.