STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

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890 Drilling and Well Completions
Table 4-1 15 gives the performance characteristics for various circulation
flowrates for the 5:6 lobe profile, 6 $-in. outside diameter positive displacement
motor. Figure 4-205 shows the performance of the 5:6 lobe profile positive
displacement motor at a circulation flow rate of 400 gal/min.
The positive displacement motor whose performance characteristics are given
in Table 4-114 is a 1:2 lobe profile motor. This lobe profile design is usually
used for deviation control operations. The 1:2 lobe profile design yields a downhole
motor with high rotary speeds and low torque. Such a combination is very
desirable for the directional driller. The low torque minimizes the compensation
that must be made in course planning which must be made for the reaction
torque in the lower part of the drill string. This reactive torque when severe
can create difficulties in deviation control planning. The tradeoff is, however,
that higher speed reduces the bit life, especially roller rock bit life.
The positive displacement motor whose performance characteristics are given
in Table 4-115 is a 5:6 lobe profile motor. This lobe profile design is usually
used for straight hole drilling with roller rock bits, or for deviation control
operations where high torque polycrystalline diamond compact bit or diamond
bits are used for deviation control operations.
Example 3
A 6+-in. outside diameter positive displacement motor of a 1:2 lobe profile
design (where performance data are given in Table 4-114) has rotor eccentricity
of 0.60 in., a reference diameter (rotor shaft diameter) of 2.48 in. and a rotor
pitch of 38.0 in. If the pressure drop across the motor is determined to be 500 psi
at a circulation flowrate of 350 gal/min with 12.0 lb/gal, find the torque, rotational
speed and the horsepower of the motor.
Torque. Equation 4-160 gives the fluid cross-sectional area of the motor, which is
A = 2(0.6)(2.48)
= 2.98 in.*
Equation 4-159 gives the specific displacement of the motor, which is
Table 4-115
Positive Displacement Motor, 6%-in. Outside Diameter,
5:6 Lobe Profile, Five Motor Chambers
Circulation Maximum Maximum
Rate Speed Dlff erential Torque Maximum
(gpm) (rpm) Pressure (psi) (ft-lbs) Horsepower
200
250
300
350
400
97
122
146
170
195
580
580
580
580
580
2540
2540
2540
2540
2540
47
59
71
82
94
Courtesy Eastman-Christensen