Screw pump rotor and method of reducing slip flow

Abstract

A pump rotor for a screw pump includes a shaft, a first set of threads disposed on a portion of an outer surface of the shaft, at least one thread of the first set of threads including a groove disposed on an end portion thereof, and a ring seal disposed on the groove such that the ring seal is configured to protrude outwardly from the groove and to rest against an inner surface of a liner of the screw pump, and the groove is sized so as to allow the ring seal to move radially with respect to the plurality of threads as the rotor is deflected.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates in general to screw pumps, and, more particularly, to improved screw pump rotors and methods of reducing slip flow in screw pumps.[0003]2. Description of the Related Art[0004]In the exploration for oil and gas the need to transport fluids (oil, water, gas, and foreign solids) from a wellhead to distant processing and / or storage facilities (instead of building new processing facilities near the wellheads) is well understood. Twin-screw pumps are increasingly being used to aid in the production of these wellhead fluids, resulting in increased production by lowering the pressure at the exit of the wellhead as well as a greater total recovery from the reservoir by allowing lower final reservoir pressures before abandoning production.[0005]FIG. 1 illustrates a conventional twin-screw pump 10. This figure is presented simply to illustrate the main components of a twin-screw pump and should not be...

AI Technical Summary

Benefits of technology

[0013]As such, those skilled in the art will appreciate that the conception, upon which disclosure is based, may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

[0014]Further, the purpose of the foregoing Abstract is to enable the U.S

Problems solved by technology

The quantity of fluid that does escape from the outlet side of the rotor back toward the inlet represents the pump slip flow, which is known to decrease the pump volumetric efficiency.

As understood by those of ordinary skill in the applicable arts, conventional twin-screw multiphase pumps face significant challenges.

First, assuming a fixed pressure rise per stage, as the total pressure rise requirement increases, the rotor length has to increase, resulting in an increased rotor deflection under the imposed pressure loading thereby creating a more eccentric alignment of the screws within the liner resulting in excessive slip between the screw rotor and the pump liner, if not contact and rubbing.

Secondly, as the pump slip flow increases, sand particulates trapped in the slip flow leads to increased erosion / abrasion within the pump, particularly at the rotor tips by a phenomenon referred to as jetting.

Such erosion / abrasion further leads to deterioration of the clearance profile and an increase in the pump slip flow.

Finally, during periods of operation in which the transported fluids have a high gas-volume fraction, the temperature of the flow exiting the pump rises due to the heat generated during compression, leading to reduced clearances in the last pump stages due to variations in thermal expansion of the various pump parts, thereby possibly resulting in catastrophic seizure.

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