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Mud Pumps 67

Casing Depth

Hole Depth
Casing ID
Drill Pipe OD Open Hole OD

Drill Pipe ID

Collar Length
Drill Collar OD

Drill Collar ID

Figure 3.3 Borehole configuration at the total depth.

3.3.3 Circulating Pressure
The maximum expected circulating pressure is the total frictional pressure
loss and pressure drop at the bit at the total hole depth. The frictional
pressure loss depends on the fluid properties, the flow velocity, the flow
regime, and the length of the flow path. Under normal drilling condi-
tions, turbulent flow exists inside the surface equipment, the drill pipe,
the drill collar, and the annulus outside the drill collar. Laminar flow nor-
mally exists in the annulus outside the drill pipe. The pressure loss in