Page 612 - Air and Gas Drilling Manual

11-50 Air and Gas Drilling Manual

Figure 11-13: Schematic cutaway of a downhole pneumatic turbine motor (courtesy of
Rift Pneumatics Incorporated).
The downhole pneumatic turbine motors must be operated with a junk screen
above the turbine section when drilling deep wells. This screen will catch any large
particles of pipe scale or other foreign matter before they can lodge in the turbine
stator and rotor.
These downhole turbine motors are more mechanically complicated than either
the downhole air hammer or the downhole positive displacement motor. Therefore,
it is necessary to manage the various drillings string forces on the BHA (including
the motor) in order to prevent motor damage.
Like the downhole positive displacement motor the downhole turbine motor
may require drill bit nozzles to choke the exhaust of the turbine device [3]. This is