DRILL BIT, SYSTEM, AND METHOD FOR DRILLING A BOREHOLE IN AN EARTH FORMATION

摘要

A drill bit for drilling a borehole in an earth formation, the drill bit having a central longitudinal axis and being operable by applying at least a rotary motion about the central longitudinal axis and optionally applying longitudinal reciprocal movement to the drill bit so as to exert a percussiv e force on the borehole bottom, the drill bit comprising a surface provided wi th a plurality of shear cutters (9) having a rake surface arranged to induce a scraping movement along the borehole bottom upon application of the rotary motion, the rake surface during operation facing the direction of rotation a t a back-rake angle of less than 90~ wherein the backrake angle is defined as the angle included between the projection of a line perpendicular to said ra ke surface on a plane defined by the central longitudinal axis and the directio n of the tangential velocity component of the shear cutter and a plane perpendicular to said longitudinal axis, whereby one or more of the shear cutters is provided with a pre-cut flat impact surface (19) essentially parallel to the plane perpendicular to the longitudinal axis.