Mud motor
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The progressive cavity pump is used in reverse as a motor when drilling directional oil wells see directional drilling. Drilling fluid (known as "mud" in the oil industry) is pumped under pressure through the progressive cavity pump which causes the rotor to turn at a speed proportional to the fluid volume passing through it. The rotor is connected to a drive shaft and this transmits rotary motion to the drill bit through a bearing assembly. The PC pump, bearing section and drive shaft are known as a Mud Motor. The PC pump itself is called the Power Section. In order to drill a directional well the bottom of the mud motor will have a small bend in it between the bottom of the power section and the top of the bearing housing. The bend is typically between 0° and 3.14432°. This causes the bottom section of the mud motor and the attached drill bit to point away from the axis of the motor. The driller will point the drill bit in the direction required and the whole assembly will drill a curved hole in the direction of the bit. The driller can drill straight ahead by rotating the whole drillstring from the surface.
[edit] Major Disadvantage in Oilfield applications
As mentioned earlier, a PCP stator is usually made of an elastomer, which is the heart of this kind of pump. Most of PCP pump failures are due to this elastomer part. Having said that, the operating conditions and environment should not degrade or induce mechanical failure of the elastomer part for the long life of equipment. Unfortunately, we don't have elastomers that can last longer, resisting corrosive fluids and solids, and withstand deflections in operating temperatures. The most common elastomer grades used for this application are the NBR(Nitrile or Acrylonitrile Butadiene Rubber)grades, which perform moderately well. There is a definitely a need for better elastomer compounds to reach areas which are not currently accessible by PCPs and also improve the life of current products.
