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Leakage of a Multistage Self-compensating Soft Plunger Pump under Different Methods

As a new type of crude oil recovery and lifting equipment, a multistage self-compensating soft plunger pump, which is suitable for alkaline-surfactant-polymer (ASP) flooding oil wells, has advantages over conventional pumping equipment. Owing to the existence of a soft plunger-pump barrel pair clearance, the pump will inevitably leak under the influence of alternating load factors, and the leakage is the main parameter in its operation. To explore the coincident relationship between the leakage of a multistage self-compensating soft plunger pump and different calculation methods, a numerical simulation model of vertical annular slit flow between a self-compensating soft plunger and a pump barrel was proposed in the study. Through the use of the Euler-Lagrange equation to describe the displacement of interface between fluid and solid, unidirectional and bidirectional fluid-structure coupling methods were presented, and the leakage distribution of a multistage self-compensating soft piston pump was determined. At the same time, a theoretical calculation model of the leakage of a multistage self-compensating soft plunger pump was obtained on the basis of hydrodynamics and the mass conservation law. Theoretical analysis, numerical simulation, and experimental study were performed to explore the influence of parameters, including the structural parameter of soft plunger length and the differential pressure operation parameter, on leakage. Meanwhile, the data of unidirectional fluid-structure coupling, bidirectional fluid-structure coupling, and theoretical calculation were compared with test results, and the optimal calculation method was proposed. Results demonstrate that under different initial clearance conditions between the soft plunger and the cylinder pair, the leakage of the pump and the length of the soft plunger are negatively correlated, that is, the larger the length of the soft plunger is, the smaller the leakage is. The pump leakage increases with the increase in pressure difference, but the rate of change of the leakage decreases gradually, which is also reflected in the change in the volume efficiency of the soft piston pump. The leakage of the multistage soft piston pump calculated by numerical simulation of bidirectional fluid-structure coupling is in the highest agreement with the leakage calculated using the experimental test method, and the difference between the two methods is within the allowable range. Therefore, the bidirectional fluid-structure coupling method adopted in this study is effective in analyzing the pressure characteristics and leakage of the multistage soft plunger pump and the proposed method provides engineering application value.