BULL BIT Russian patent published in 1998 - IPC

FIELD: drilling of deep wells of large diameter, in particular, rock-cutting tools operating by individual drive. SUBSTANCE: bull bit has body 1 which consists of set of weighed members 2 interconnected by ties. Located under lower end of body 1 is rock-cutting tool 4. Cross-section of body 1 may be oval, or rectangular, or rhomboid, or part of circumference confined by parallel chords symmetrical with respect to cross-section large axis. Downhole motors pass through body 1. There may be two, three or four downhole motors located in plane running through large axis of cross-section of body 1. Downhole motors may be in the form of screw motors or in the form of electric motors. Downhole motors are joined with rock-cutting tool 4. Attached to body 1 is calibrator 7 located above bit 4 in close proximity to it. Calibrator 7 has two blades 7 located in plane square to plane running through large axis of cross-section of body 1. Maximum size of cross-section of body 1 with respect to bit diameter is related as: 0.87 ≤ a/D ≤ 0.97, where a is maximum diameter of body cross-section, mm; D is bit diameter, mm. EFFECT: higher efficiency of drilling. 3 cl, 5 dwg