| 摘要 |
<p>A drag-type drill bit for drilling holes in subsurface formations comprises a bit body (70) having an end face (71) and a shank (72) for connection to a drill string, a number of blades (73, 74) upstanding from the end face of the bit body and extending outwardly away from the axis of rotation of the bit, a number of cutters (76) mounted on each blade, and a number of nozzles (81) in the bit body for delivering drilling fluid for cooling and cleaning the cutters. The blades include primary blades (73) which, at their outer ends, are spaced apart around a peripheral gauge portion (75) of the bit, and secondary blades (74) which are spaced circumferentially between adjacent primary blades, each secondary blade having an outer end which terminates at a location inwardly of the gauge portion (75) of the bit. One of said nozzles (81) is located adjacent each blade (73, 74). Each primary blade (73) and associated secondary blade (74) may be equivalent, in terms of their combined contribution to the cutting profile, to a single blade which extends continuously from the centre of the bit body to the gauge, but the separation of the blades facilitates the flow of drilling fluid over and between the blades. Also, the increased number of blades may enhance the stability of the drill bit and reduce vibration. <IMAGE></p> |
