STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

892 Drilling and Well Completions
Horsepower. The horsepower the motor produces is obtained from Equation
4-164. This is
350( 500)
HP = (0.80)
1714
= 82
Planning for a positive displacement motor run and actually drilling with such
a motor is easier than with a turbine motor. This is mainly due to the fact that
when a positive displacement motor is being operated, the operator can know
the operating torque and rotation speed via surface data. The standpipe pressure
will yield the pressure drop through the motor, thus the torque. The circulation
flowrate will yield the rotational speed.
Example 4
A 6 4 -in. outside diameter positive displacement motor (whose performance
data are given in Tables 4-114 and 4-115) is to be used for a deviation control
direction drill operation. The motor will use an 84411. diameter roller rock bit for
the drilling operation. The directional run is to take place at a depth of 10,600 ft
(measured depth). The rock formation to be drilled is classified as medium, and it
is anticipated that 30 ft/hr will be the maximum possible drilling rate. The mud
weight is to be 11.6 Ib/gal. The drilling rig has a National Supply Company
duplex mud pump Model E-700 available. The details of this pump are given
in Table 4-116 (also see the section titled “Mud Pumps”). Because this is a deviation
control run, the 1:2 lobe profile positive displacement motor will be used
since it has the lowest torque for a given circulation flowrate (see Table 4-114).
Determine the appropriate circulation flowrate to be used for the roller rock bit,
positive displacement motor combination and the appropriate liner size to be used
in the duplex pump. Also, prepare the positive displacement motor performance
graph for the chosen circulation flowrate. Determine the bit nozzle sizes.
Bit Pressure LOSS. It is necessary to choose the bit pressure loss such that the
thrust load created in combination with the weight on bit will yield an on-bottom
load on the motor thrust bearings, which is less than the maximum allowable
load for the bearings. Since this is a deviation control run and, therefore, the
motor will be drilling only a relatively short time and distance, the motor thrust
bearings will be operated at their maximum rated load for on-bottom operation.
Figure 4-206 shows that maximum allowable motor thrust bearing load is about
Table 4-116
Duplex Mud Pump, Model E-700, National Supply Company, Example 4
Input Horsepower 825, Maximum Strokes per Minute, 65 Length of Stroke, 16 Inches
Output per Stroke (gals) 6.14 6.77 7.44 8.13 8.85 9.60
Maximum Pressure (psi) 3000 2450 2085 1780 1535 1260