| 摘要 |
A rotary drill bit for use in drilling or coring deep holes in subsurface formations comprises a bit body having a leading face and a gauge region, cutting elements mounted at the leading face of the bit body, and a passage in the bit body communicating with nozzles in the leading face of the bit body for supplying drilling fluid to the face for cooling and cleaning the cutting elements. Certain of the cutting elements each comprise a preform cutting element having a superhard front cutting face providing a cutting edge, and others of the cutting elements each comprise particles of hard material embedded in a front layer of a less hard material to form a cutting layer having a cutting edge. The distribution of the cutting elements over the leading face of the bit is such that the proportion of the combined length of cutting edges provided by preform cutting elements to the combined length of cutting edges provided by embedded-particle cutting elements generally increases with distance from the central axis of rotation of the bit.
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