In this paper the effect of an offset of a 3-cone bit on drilling performance was studied. Bits with diameter of 3
3/
4in. were tested by a rotary drilling machine at room temperature and atmospheric pressure using water as circulating fluid. A bit with offset angle of 4 deg. was compared with a bit without offset angle.
To investigate the effect of an offset of a 3-cone bit, such parameters as drilling rate, torque, power and specific energy were measured. Results obtained are as follows: (1) a bit with offset angle penetrates faster with greater torque than a bit without offset angle, (2) an effect of offset angle on drilling rate decreases as compressive strength of rock sample increases, (3) drilling power and specific energy of a bit with offset angle is greater than those of a bit without offset angle, and (4) about a slope of drilling power to penetration rate, the slope of offset bit is greater than that of non-offset bit, and difference between them increases with increasing compressive strength of rock samples.
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