Read and translate the text. Fill out the K and the W columns prior to reading and then use the L column to take notes while reading.

Fill out the K and the W columns prior to reading and then use the L column to take notes while reading.

K	W	L
What do you KNOW about bits?	What do you WANT to know about bits?	What did you LEARN about bits?

Two main types of bits have been developed through the years for more efficient drilling. Roller cone, or rock, bits have cone-shaped steel devices called cones that are free to turn as the bit rotates. Most bits have three cones, although some have two and some have four. Bit manufacturers either cut teeth out of the cones or insert very hard tungsten carbide buttons into the cones.The teeth are responsible for actually cutting or gouging out the formation as the bit is rotated. All bits have passages drilled through them to permit drilling fluid to exit. Most bits have nozzles that direct a high-velocity stream or jet of drilling fluid to the sides and bottom of each cone so that rock cuttings are swept out of the way as the bit drills.

Diamond bits do not have cones, nor do they have teeth.Instead, several diamonds are embedded into the bottom and sides of the bit. Since diamonds are so hard, diamond bits are especially suited for drilling hard rock formations but can also be used effectively on soft formations.

Diamond bits are designed to crush nonabrasive rocks of medium hardness and hard rocks by abrasion (microcutting). Diamond bit consists of steel housing with con­necting toll-Joint thread and shaped diamond-bearing head (matrix). Matrix is divided into sectors with radial (or spiral) flushing channels, which are connected to the bit hous­ing cavity through flushing porta.

Diameters of diamond bits art 2- 3 mm less than relevant diameters of roller-cutter bits. This is made to create conditions required for transition to drilling with diamond bits after roller-cutter bits, which, as a rule, are decreased in diameter with deterioration. Key advantages of diamond bits are good centralizing capacity on the well bottom and development of circular bottom hole (opposite to triangular bottom hole with rounded tops when drilling with roller-cutter bits).

Significant disadvantages of diamond bits include: first, extremely low drilling rate. Maximal mechanical drilling rate, as a rule, does not exceed 3 m/h. For comparison — maximal mechanical rate of drilling with roller-cutter bits is about 120m/h. Second, diamond bits have small range of application (abrasive rocks are excluded) and third, higher requirements to preliminary preparation of well bore and bottom are set.

Дата добавления: 2015-10-24