What are Positive Displacement Mud Motors in Drilling for Oil and Gas?

Positive-Displacement Motors (PDM) make use of a power generation section which is made up of a rotor/stator combination. In order to move a rotor part,  a PDM requires hydraulic power from drilling fluid flowing through the power generation part. With a PDM, the stator and rotor work in tandem in the same way that gears do. The stator acts as the outer gear, and is made from a moulded elastomer featuring at least two lobes. The OD of the elastomer is protected by a secure metal casing. The rotor is positioned within the stator, and acts as an internal gear. This rotor is made of metal, and will have one less gear or lobe than the stator. Because of this difference, a cavity is created which is filled with drilling fluid when the PDM is downhole. This cavity acts as a wedge when it is put under pressure, and because the drilling fluid itself can’t be compressed, the force applied to the top of the wedge causes the rotor to move.

Mud Motor

Figure 1 – Mud Motor

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How to Determine Mud Motor Failure

Mud motor failure downhole may be happened from time to time. The questions that are usually raised are things like “How do I know if the mud motor fails down hole?” and “What indications will I see that this has happened?” etc. Due to this, I would like to share my personal experience regarding mud motor failure and its symptoms.

The following signs indicate that you may be faced with downhole mud motor breakdown.

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