Oil and gas wells are typically drilled by a process of rotary drilling. An earth-boring drill bit is mounted on the lower end of a drill string. Weight is applied on the drill bit, and the bit is rotated by rotating the drill string at the surface, by actuation of a downhole motor, or both. The rotating drill bit includes cutters that engage the earthen formation to form a borehole. The bit can be guided to some extent using an optional directional drilling assembly located downhole in the drill string, to form the borehole along a predetermined path toward a target zone.
Many different types of drill bits and cutting structures for bits have been developed and found useful in drilling such boreholes. Two predominate types of rock bits are roller cone bits and fixed cutter bits. Both types of bits may include hardened elements that engage the earth to cut and liberate earthen materials such as rock. Roller cone bits include cutters that cut earth by gouging-scraping or chipping-crushing action. Fixed cutter bits include cutters that cut earth by shearing action.
While a drill bit is rotated, drilling fluid is pumped through the drill string and directed out of the drill bit. Drill bits typically include nozzles or fixed ports spaced about the bit face that serve to inject drilling fluid into the flow passageways between the several blades or amongst the roller cones. The flowing fluid performs several important functions. The fluid removes formation cuttings from the drill bit's cutting structure. Otherwise, accumulation of formation materials on the cutting structure may reduce or prevent the penetration of the cutting structure into the formation. In addition, the fluid removes formation materials cut from the bottom of the hole. Failure to remove formation materials from the bottom of the hole may result in subsequent passes by cutting structure to re-cut the same materials, thus reducing cutting rate and potentially increasing wear on the cutting surfaces. The drilling fluid and cuttings removed from the bit face and from the bottom of the hole are forced from the bottom of the borehole to the surface through the annulus that exists between the drill string and the borehole sidewall. Further, the fluid removes heat, caused by contact with the formation, from the cutters in order to prolong cutter life.