Positive Displacement Motors (PDM)

Rene Moineau, a French engineer first invented and obtained several modified patents for a rotary type pump between 1930 and 1948. The pumps he developed were extensively used in the world war planes as superchargers. The first commercial PDM was introduced to the petroleum industry in the late 1950s. Their use increased in the late 1960s for the directional drilling application. However, their use has accelerated greatly with the present coiled tubing drilling.

The basic parts of a Moineau type motor involve a stator housing and a shaft enclosed in a casing. The center shaft has a wavy shaped cross section and each wave corresponds to a lobe. The housing which is contained in a casing accommodates the wavy shaped rotor, whose cross section is also wave shaped but the number of lobes is one more than in the shaft. When the shaft is inserted in the housing, the difference in their respective pitches creates a series of cavities. Drilling fluid pumped travels in a helical path between the shaft and the housing. In this process the drilling fluid displaces the shaft, forcing it to rotate clockwise as the mud continues to flow through the helical path.