The drill collar is at the bottom of the drill string and is the main component of the lower drill assembly. Its main features are large wall thickness (generally 38 ~ 53mm, equivalent to 4-6 times the wall thickness of the drill pipe), and greater gravity and stiffness. In order to facilitate the work of lifting and lowering, elevator grooves and slip grooves can be processed on the outer surface of the internal thread of the drill collar. Made of forged AISI4145H chromium-molybdenum alloy steel to effectively control the chemical composition and trace element content.
The effect of the drill collar:
(1) Apply pressure to the drill bit;
(2) Ensure the necessary strength under compression conditions;
(3) Reduce the vibration, swing, and runout of the drill, and make the drill work smoothly;
(4) Control well deviation.
Drill collars are generally divided into three types: slick drill collars, spiral drill collars, and non-magnetic drill collars.
(1) The slick drill collar is a smooth thick-walled round pipe, and the connecting threads are processed at both ends.
(2) Spiral drill collars process three right-handed spiral grooves on the outer cylindrical surface of the circular collar to reduce the contact area with the well wall and effectively prevent pressure-drilling
(3) Non-magnetic drill collar is mainly used for monitoring during oil drilling. The structure is the same as the overall drill collar. The non-magnetic drill collar is made of P530 or P550 alloy steel, which is forged after strict chemical composition analysis. The material's mechanical property test can ensure that the hardness, toughness, impact value and corrosion resistance meet the standards, and it has good low magnetic permeability and good machining performance.
In order to facilitate the work of lifting and lowering, elevator grooves and slip grooves can be processed on the outer surface of the internal thread of the drill collar.
Executive standard: API7-1