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74 Part I Liquid Drilling Systems

Illustrative Example 3.3
For the data in Illustrative Examples 3.1 and 3.2, determine the required
horsepower rating of the pump.

Solution
The pump should be able to provide adequate horsepower while drilling all
hole sections. The extreme hole conditions occur when the surface hole
and the total hole depth are drilled. Drilling the surface hole requires the
highest mud flow, and drilling at the total depth requires the highest pump
pressure.
Surface Hole Drilling. Illustrative Example 3.1 shows that the minimum required
3
flow rate to drill the surface hole is 990 gpm (3.75 m /min). The required
pressure at the bottom of the hole section with 60 feet (18.3 m) of a 7-inch
(178 mm) drill collar is calculated using the spreadsheet program Pump
Pressure.xls. The result of the pressure loss is 364 psi (2,509 kPa). Considering
a pressure drop at the bit of twice the pressure loss, the circulating pressure
will be 1,092 psi (7,529 kPa). Substituting these data into Eq. (3.9) gives

P h = ð990Þð1,092Þ = 631 hp
1,714
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Drilling at the Total Depth. Using the flow rate of 350 gpm (1.325 m /min) and
the required pressure of 3,461 psi (23,863 kPa) calculated with the spread-
sheet program Pump Pressure.xls, Eq. (3.9) gives
P h = ð350Þð3,641Þ = 743 hp
1,714

Therefore, the minimum required horsepower rating of the pump is 743 hp.

3.5 CAPACITIES OF MUD PUMPS

The two types of piston strokes in mud pumps are the single-action
piston stroke and the double-action piston stroke, which are shown in
Figures 3.6 and 3.7. The double-action stroke is used for duplex (two
pistons) pumps. The single-action stroke is used for triplex pumps.
Normally, duplex pumps can handle higher flow rates, and triplex pumps
can provide higher pressure. The discharged flow rate depends on several
parameters, including the liner size, the rod size, the stroke length, the