STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

882
Drilling and Well Completions
4oM)
-
Circulation Rate 340 gpm
Mud WeQht 16.2 pW
400
2000
-
v Q
I- t
3000
ZOO0
4 --D Pressure
300
200
1500
G
B
f
u)
i
c
1000 E
5
E
0
IO00
100
500
0
500 lo00 1500 2000
Bit Speed (rpm)
Figure 4-200. Turbine motor, 6Wn. outside diameter, two motor sections,
212 stages, 340 galhin, 16.2-lb/gal mud weight, Example 2. (Courtesy Smith
International, Inc.)
(text continued from page 876)
Positive Displacement Motor
Figure 4-201 shows the typical rigid rotor and flexible elastomer stator
configuration for a single chamber of a multichambered downhole positive
displacement motor section. All the positive displacement motors presently in
commercial use are of Moineau type, which uses a stator made of an elastomer.
The rotor is made of a rigid material such as steel and is fabricated in a helical
shape. The activating drilling mud, freshwater, aerated mud, foam or misted air
is pumped at rather high velocity through the motor section, which, because of
the eccentricity of the rotor and stator configuration, and the flexibility of the
stator, allows the hydraulic pressure of the flowing fluid to impart a torque to
the rotor. As the rotor rotates the fluid is passed from chamber to chamber (a
chamber is a lengthwise repeat of the motor). These chambers are separate
entities and as one opens up to accept fluid from the preceding, the preceding
closes up. This is the concept of the positive displacement motor.
Design
The rotational energy of the positive displacement motor is provided by the
flowing fluid, which rotates and imparts torque to the drill bit. Figure 4-202
shows the typical complete downhole positive displacement motor.