STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Downhole Motors 875
Similarly, the pressure drop across the bit to produce the above hydraulic
horsepower at a circulation flowrate of 300 gal/min is
APb =
85.05( 1,7 14)
300
= 486 psi
The pressure drop across the bit at a circulation flowrate of 400 Ib/gal is
Apb = 364 psi
The pressure drop across the bit at a circulation flowrate of 500 gal/min
Apb = 292 psi
Total Pressure LOSS. Using Table 4-110 and Equations 4-150 and 4-151, the
pressure loss across the turbine motor can be determined for the various
circulation flowrates and the mud weight of 16.2 lb/gal. These data together
with the above bit pressure loss data are presented in Table 4-1 13. Also presented
in Table 4-113 are the component pressure losses of the system for the various
circulation f lowrates considered. The total pressure loss tabulated in the lower
row represents the surface standpipe pressure when operating at the various
circulation flowrates.
Pump Limitations. Table 4-112 shows there are five possible liner sizes that can
be used on the Model 10-P-130 mud pump. Each liner size must be considered
to obtain the optimum circulation flowrate and appropriate liner size. The
maximum pressure available for each liner size will be reduced by a safety factor
of 0.90.* The maximum volumetric flowrate available for each liner size will
also be reduced by a volumetric efficiency factor of 0.80 and an additional safety
factor of 0.90.** Thus, from Table 4-112, the allowable maximum pressure and
allowable maximum volume, metric flowrates will be those shown in Figures 4-195
through 4-199, which are the liner sizes 5 +, 5 fr, 5 j, 6 and 6 in., respectively.
Plotted on each of these figures are the total pressure losses for the various
circulation flowrates considered. The horizontal straight line on each figure is
the allowable maximum pressure for the particular liner size. The vertical
straight line is the allowable maximum volumetric flowrate for the particular
liner size. Only circulation flowrates that are in the lower left quadrant of the
figures are practical. The highest circulation flowrate (which produces the
highest turbine motor horsepower) is found in Figure 4-197, the 5Q-in. liner.
This optimal circulation flowrate is 340 gal/min.
Turbine Motor Performance. Using the turbine motor performance data in
Table 4-110 and the scaling relationships in Equations 4-145 through 4-151, the
performance graph for the turbine motor operating with a circulation flowrate
of 340 gal/min and mud weight of 16.2 lb/gal can be prepared. This is given
in Figure 4-200.
*This safety factor is not necessary for new, well-maintained equipment
**The volumetric efficiency factor is about 0.95 for precharged pumps.