DRILL COLLAR
Drill collar is designed for creating axial load to the bit, for improving rigidity and stability of the
lower part of the drill string when drilling wells.
BASIC SIZES OF DRILL COLLARS
| Drill collar diameter, inch | Bore, inch | Tool joint thread, API |
| 3 1/8 | 11/4 | NC-23 |
| 3 1/2 | 11/2 | NC-26 |
| 4 1/8 | 2 | NC-31 |
| 4 3/4 | 2 1/4 | NC-35 |
| 5 | 2 1/4 | NC-38 |
| 6 | 2 13/16 | NC-44 |
| 6 | 2 1/4 | NC-44 |
| 6 1/4 | 2 13/16 | NC-44 |
| 6 1/4 | 2 1/4 | NC-46 |
| 6 1/2 | 2 13/16 | NC-46 |
| 6 1/2 | 2 1/4 | NC-46 |
| 6 3/4 | 2 13/16 | NC-46 |
| 7 | 2 1/4 | NC-50 |
| 7 | 2 13/16 | NC-50 |
Type of design:
- plain;
- with a recess of the elevator;
- with a recess of the elevator and power slips;
- spiral and a wide range of type mixtures.
A spiral drill collar is the most widely spread type because of its characteristics. Due to the spiral groves the contact area between the well’s wall and the pipe is diminished; the possibility of pipe’s balking is lessened and the drill stem rotation torque is increased. The spiral drill collars can be done with recesses for elevator and power slips at the same time.
Length: 30 – 31 ft ± 6 ft.
