Abbreviation for positive displacement motor, a downhole motor used in the oil field to drive the drill bit or other downhole tools during directional drilling or performance drilling applications. As drilling fluid is pumped through the positive displacement motor, it converts the hydraulic power of the fluid into mechanical power to cause the bit to rotate.
During directional drilling, this capability is used while drilling in sliding mode, when the drillstring is not rotated from the surface. Positive displacement motors can also be used for performance drilling, straight hole drilling, coring, underreaming, and milling operations. In straight hole drilling, the motor functions as a drilling performance tool to increase the rate of penetration and reduce casing wear by minimizing drillstring rotation.