Square Drill Collars

Square drill collars accomplish four goals: (1) they provide continuous centralization over their length, (2) they maximize bending resistance (stiffness), (3) they maximize torsional damping, and (4) they minimize axial vibrations. On the down side, they are expensive to buy and to maintain. They usually create high rotary torque. They grind drill bit cuttings and cavings to fines which radically increases mud consumption. They are difficult to fish. Note that a 11.2 inches round collar has the same stiffness as a 12.125 inches square collar.

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