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United States Patent 5779451
Douris , ê et al. July 14, 1998

Power efficient multi-stage twin screw pump

Hatton July 14, 1998

Abstract

There is disclosed an apparatus for pumping multiphase fluids in oil field production, particularly a twin-screw pump for providing a large pressure boost to high gas-fraction inlet streams. The pump includes a housing having an internal rotor enclosure, the enclosure having an inlet and an outlet and a plurality of rotors operably contained in the enclosure. Each rotor has a shaft and a plurality of outwardly extending threads affixed thereon, the rotors being shaped to provide a non-uniform volumetric delivery rate along the length of each rotor. The pump also has means for rotating the rotors, whereby a fluid stream entering from the inlet is subjected to a pumping action to transport the fluid stream to exit the rotor enclosure through the outlet. In one embodiment, the rotors have a plurality of threaded pumping stages separated by unthreaded non-pumping chambers. Further, the threads of each pumping stage may have a different screw profile to provide progressively decreasing inlet volumetric delivery rates from the inlet to the outlet of the rotor enclosure. The multiple stages provide better power efficiency than traditional twin-screw pumps for high-pressure boost operation at gas fractions up to 100% without seizing or loss of pressure boost.