STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Downhole Motors 893
OFF BOllOM BEARING LOAD (1000 LBS)
5
MAXIMUM RECOMMENDED BEARING LOAD
0
5
5 10 15 20
ON BOTTOM BEARING LOAD (1000 LBS)
MAXIMUM RECOMMENDED BEARING LOAD
Figure 4-206. Hydraulic thrust and indicated weight balance for positive
displacement motor. (Courtesy Smith International, Inc.)
6,000 lb. To have the maximum weight on bit, the maximum recommended bit
pressure loss of 500 psi will be used. This will give maximum weight on bit of
about 12,000 Ib. The higher bit pressure loss will, of course, give the higher
cutting face cleaning via jetting force (relative to the lower recommended bit
pressure losses).
Total Pressure LOSS. Since bit life is not an issue in a short deviation control
motor run operation, it is desirable to operate the positive displacement motor
at as high a power level as possible during the run. The motor has a maximum
pressure loss with which it can operate. This is 580 psi (see Table 4-114). It will
be assumed that the motor will be operated at the 580 psi pressure loss in order
to maximize the torque output of the motor. To obtain the highest horsepower
for the motor, the highest circulation flowrate possible while operating within
the constraints of the surface mud pump should be obtained. To obtain this
highest possible, or optimal, circulation flowrate, the total pressure losses for
the circulation system must be obtained for various circulation flowrates. These
total pressure losses tabulated in the lower row of Table 4-1 17 represent the
surface standpipe pressure when operating at the various circulation flowrates.
Pump Limitations. Table 4-116 shows there are six possible liner sizes that can
be used on the Model E-700 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 4-116, the allowable maximum pressures and
allowable maximum volumetric flowrates will be those shown in Figures 4-207
through 4-212, which are the liner sizes 5+, 6, 6$, 64 and 7 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