1. What are the characteristics and functions of drill collars?
Its main characteristics are large wall thickness (generally 38 to 53 mm, equivalent to 4 to 6 times the wall thickness of the drill pipe), and large weight and stiffness. The function is:
(1) Apply drilling pressure to the drill bit;
(2) Ensure the necessary strength under compression conditions;
(3) Reduce the vibration, swing, and beating of the drill bit to make the drill bit work smoothly;
(4) Control well deviation.
2. Why do the large-size drill collars (8in, 9in) and the upper part of the Kelly pipe use the regular buckle type?
Because large-size collars (8in, 9in) are heavy and large, the back-button joint with the upper part of the kelly can bear a large torque, while the regular button-type connection has high strength and can withstand large torque, so the regular button-type should be used.
3. What are the functions of spiral collars and non-magnetic drill collars?
The former can be used to drill both vertical wells and directional wells.
The latter are used to drill directional wells. Because drilling directional wells requires an inclination measuring instrument, it cannot be interfered with by magnetism.
4. What are the inner diameters and mass per meter of 53/4in, 61/4in, and 7in drill collars according to API specifications?
The inner diameter of 53/4in collar is 71.44mm, and the mass per meter is 99.50kg. The inner diameter of 61/4in collar is 74.44mm, and the mass per meter is 123.56kg. The inner diameter of 7in product is 71.44mm, and the mass per meter is 163.20kg.
5. What is the difference between the fatigue failure of drilling collars and the fatigue failure of drill pipes?
The former is also prone to fatigue damage when rotating in a bent state, but they are different from drill pipes. For drill pipes, due to the high strength and stiffness of the joints, bending is often concentrated on the drill pipe body near the joints.
Fatigue failure generally occurs within 1.2m from the joint. The stiff body of a collar is greater than that of the joint, and the stress is concentrated on the weaker joint. Therefore, most fractures occur at the joint. Table 6 Conditions for scrapping due to wear on drill pipe body
6. What is the definition of scrap standards?
Drill collars should be scrapped if any of the following conditions occur:
(1) It is bent and cannot reach the straightness allowed by Table 3-7 after straightening;
(2) The water eye is blocked and cannot be opened;
(3) There is a dissection in the body and cannot be removed;
(4) The scars on the body exceed the standard;
(5) After uniform wear or eccentric wear, the outer diameter is smaller than the specified chamfer diameter;
(6) The total length of repairs that have been performed multiple times is less than 8.2m;
(7) The sealing end face of the external thread and internal thread of is less than 200mm from the end face of the spiral.
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