A drill collar is located at the lowest part of the drill string and is a major component of the BHA. Its main characteristics are large wall thickness (generally 38~53mm, equivalent to 4~6 times of the wall thickness of drill pipe), with greater gravity and stiffness. To facilitate tripping, a clamp slot and a slip slot can be machinedon the outer surface of the internal thread of the drill collar。

(1) apply bit weight to the bit;

(2) to ensure the necessary strength under compression conditions;

(3) reduce the vibration, swing, and jump of the drill bit, so that the drill work smoothly;

(4) Control well deviation.

There are three types of drill collars: spiral drill collars, non-magnetic drill collars and integral drill collars.

(1) The integral drill collars are smooth thick-walled round pipes with threaded connections at both ends.

(2) Three right-turning spiral grooves were made on the outer cylindrical surface of the drill collar to reduce the contact area with the wellbore wall and effectively prevent the drilling stuck by pressure difference

(3) The non-magnetic drill collar is mainly used for monitoring in the process of oil drilling, and the structure is the same as the integral drill collar. The non-magnetic drill collars are manufactured from N1310 low carbon alloy steel, which is forged after rigorous chemical analysis. The mechanical properties of the material can be tested to ensure that the hardness, toughness, impact value and corrosion resistance meet the standards, with good low magnetic permeability and good mechanical processing properties.

To facilitate tripping, a clamp slot and a slip slot can be machinedon the outer surface of the internal thread of the drill collar.

Executive standard: SY5144-2007.API7-1