Downhole Motors - Positive Displacement Motors : Types of Positive Displacement Motors

Types of Positive Displacement Motors
PDMs come in various configurations. As has been mentioned previously,
the stator will have one more lobe than the rotor. The first types of PDMs,
and the simplest, are 1/2 motors. These generally give medium to low
torque output and medium to high rotary speed. Torque output is directly
proportional to pressure drop across the motor. The
1/2 motors have good applications in performance drilling with a PDC,
diamond, or TSP-type bits. Some shorter models are used for directional
purposes.

Multi-lobe motors have high torque output and relatively slow speed.
Therefore, they have good applications with roller cone bits and for coring.
Such motors are also suitable for use with PDC bits, especially the large
cutter types which require a good torque output to be efficient. These tools,
being fairly short, also have good directional applications with bent subs as
the deflection device. Multi-lobe motors may be constructed with a hollow
rotor and a nozzle or blank placed in a holding device at the top. The nozzle
allows for high flow rates to be accommodated by by-passing the excess
flow from the motor section and the fluid will exit through the bit.