Leakage Mechanism of Soft Plunger Pumps

Jestr JOURNAL OF Journal of Engineering Science and Technology Review 11 (6) (2018) 70 - 76 Engineering Science and Technology Review Research Article www.jestr.org Leakage Mechanism of Soft Plunger Pumps Chunying Hu1,2, Guoyou Han1,*, Weijian Chen1, Weidong Ye1, and Daoquan Han 1,3 1 School of Mechanical Science and Engineering, Northeast Petroleum University, Daqing 163318, China 2 College of Engineering, Heilongjiang Bayi Agricultural University, Daqing 163319, China 3 Khartoum Refinery Co. Ltd, Khartoum North 12211, Sudan Received 7 October 2018; Accepted 19 December 2018 ___________________________________________________________________________________________ Abstract As a new type of petroleum extraction device, soft plunger pumps can effectively avoid the stuck problem of pump and realize the lift of underground petroleum. Meanwhile, soft plunger pumps have strong adaptability to wells using Alkaline surfactant polymer flooding. Non-metallic sealing rings have experienced frequent leakage under the influence of pressure difference due to the increase in the extraction difficulty and the submergence depth, thereby reducing their pumping efficiency eventually. Therefore, studies on the leakage of soft plunger pumps are crucial for the calculation of plunger velocity and the improvement of pumping efficiency. A model for multistage soft plunger pumps was proposed in this study to reveal the relationship between the leakage amount and the operational and structural parameters of soft plunger pumps. The finite element method was used to determine the length and thickness of the sealing ring in the paper, thereby establishing a physical model. The influence factors on the leakage amount, namely, pressure difference, velocity, medium viscosity and clearance, were analyzed on the basis of fluid dynamics and the theorem of momentum. The influences were also explored by using theoretical analysis and empirical test. In addition, a prediction model was constructed on the basis of the operational characteristics of soft plunger pumps to verify the correctness of the leakage mechanism. Results show that the leakage amount of soft plunger pumps increases with the pressure difference under the premise of constant medium viscosity, velocity and clearance, in which the leakage amount in high-viscosity medium is smaller than that in low-viscosity medium. In the pressure difference, medium viscosity and clearance remain unchanged and the volumetric efficiency of soft plunger pumps could be considerably enhanced by increasing the velocity. Given that large clearances are found to intensify pump leakage, maintaining the clearance in the range of 0.2 to 0.5mm is recommended. The study provides a theoretical basis for correctly improving the pumping efficiency of soft plunger pumps. Keywords: Soft plunger, Pump, Leakage amount ____________________________________________________________________________________________ 1. Introduction Current petroleum extraction devices mainly include plunger, screw, electric submersible, hydraulic and gas lift pumps. Among these pumps, plunger pumps, which achieve outstanding economic and social benefits, serve as the earliest and the most extensively used petroleum extraction device. Plunger pumps have been applied extensively to petroleum extraction from ordinary, deep, ultra-deep, and heavy oil wells due to their advantages of simple structure, convenient operation, high reliability, strong adaptability, excellent lifting performance and protection for oil pipes. The demand for plunger pumps has shown a trend of rapid growth, and studies on related techniques have rapidly progressed. Meanwhile, a growing number of units have participated in the study, design, production, and application of plunger pumps. Plunger pumps can be further divided into hard and soft plunger pumps based on sealing materials. Given that hard plunger pumps are easily stuck, the China University of Petroleum has presented a soft plunger pump that relies on the hydraulic pressure to realize sealing. Petroleum extraction is currently in the second or third stage when the petroleum reserves are reduced and the ______________ *E-mail address: ISSN: 1791-2377 © 2018 Eastern Macedonia and Thrace Institute of Technology. All rights reserved. doi:10.25103/jestr.116.10 extraction conditions are complicated. Petroleum reserves tend to contain some free gas. A common method to reduce the influence of free gas is to increase the submergence depth of pumps. The inlet pressure increases with the submergence depth. The rubber sealing rings experience an increase in elasticity under pressure, thereby causing fatigue failures (transiting from fatigue crack initiation to crack growth). Consequently, the pumps leak seriously and therefore fail. The leakage of pumps involves numerous factors, which not only increase the technical difficulty but also pose a tremendous challenge to the study on soft plunger pumps. Therefore, numerous studies have been conducted on the materials of sealing rings and the leakage amount and lifting performance of soft plunger pumps [1–3]. Scholars have optimized the materials of sealing rings and revealed the relationship between leakage amount and lifting performance. However, few studies have been concerned on the influences of pressure difference, velocity, medium viscosity, and geometric parameters on leakage amount, thereby distancing the physical models and operational parameters of soft plunger pumps from reality. Existing studies cannot solve the problems of pumping efficiency and lifetime. Therefore, exploring the leakage mechanism, accurately predicting the leakage, analyzing basic factors that affect the leakage amount, and clarifying the coupling Chunying Hu, Guoyou Han, Weijian Chen, Weidong Ye and Daoquan Han/ Journal of Engineering Science and Technology Review 11 (6) (2018) 70 - 76 relationship between the operational parameters and physical models of soft plunger pumps in operation are urgent. A model for multistage soft plunger pumps applicable to Alkaline surfactant polymer flooding was designed in this study to lower the pressure on single-stage plunger pumps, extend the service life of soft plunger pumps, and achieve uniform pressure at each stage. The proposed model was established by using the finite element method to analyze the leakage of soft plunger pumps under different pressure differences, velocities, medium viscosities and clearances. This study aims to predict the coupling relationship between the operational parameters and physical models of soft plunger pumps accurately, thereby providing references for the optimization of related parameters. plunger pumps based on the fluid dynamics and revealed the superiority of these plunger pumps in leakage amount. When the clearance ranged between 0.1 mm and 0.15 mm, the leakage amount of hydraulic self-sealing plunger pumps lifting polymer-containing viscoelastic fluids wa (...truncated)