Bit Face Fluid Dynamics

The waterway configuration on the face of a bit has a considerable effect on its performance. By using the same in-hole fluid circulation rate, the “Regular” (Style “W”), “Turbo” (Style “T”) and “Extra Wide” (Style “XW”) waterway configurations produce a higher fluid pressure at the bit face than the “Extra Extra Wide” (Style “XXW”), “Face Discharge” (Style “FD”) or “Slot Face Discharge” (Style “SFD”) waterway configurations. Higher fluid pressures through the input ports of the bit, that is, the fluid passages through which circulating fluid is introduced to the bit crown, may be desirable when trying to create a jetting action across the bit face to move fine cuttings. Lower fluid pressures through the input ports may be desirable where the formation being drilled is susceptible to hydraulic erosion, where the phenomenon of hydraulic lift is an issue or where fluid turbulence at the bit face hampers performance.

The effect of waterway configuration on input fluid pressure to the bit face for some common diamond impregnated core bits is illustrated in the following table:

All of the values for “Fluid Pressure Developed” given in the table above assume that the circulating fluid has a specific gravity of “1.00”.