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72 Part I Liquid Drilling Systems

Illustrative Example 3.2 (Continued )
Table 3.5 Summary of Calculated Pressures
Pressure Loss/Drop
Equipment psi MPa
Inside drill pipe 636 4.39
Inside top drill collar 96 0.66
Inside mid-drill collar 0 0
Inside bottom drill collar 15 0.10
Motor 200 1.38
Bit nozzles 2,202 15.19
Outside bottom drill collar 42 0.29
Outside mid-drill collar 0 0
Outside top drill collar 14 0.10
Drill pipe open hole annulus 73 0.50
Drill pipe cased hole annulus 181 1.25
Total circulation pressure 3,461 23.86

3.4 HORSEPOWER REQUIREMENTS

In rotary drilling, the engines that supply power are rated on
output horsepower, sometimes called brake horsepower. Fluid pumps
that receive power are rated on the basis of input horsepower. For this
reason, a 1,600-hp pump classification means that the horsepower fed
into the pump should not exceed 1,600. Output horsepower from
pumps used in rotary drilling is determined from charts of maximum
permissible surface pressure and maximum circulation rate.
Mud pumps are rated by horsepower P H and the maximum working
pressure p pm . Figure 3.5 shows a theoretical pump performance curve. The
mud hydraulic horsepower from the pump is expressed as (Moore, 1986)
qp
P h = (3.8)
1,714
where

P h = hydraulic horsepower, hp
3
q = mud flow rate, gpm or m /min
p = pump pressure, psi or kPa