As gas wells enter the mid-to-late stages of development, reservoir energy depletion causes increasingly severe liquid loading in the wellbore, markedly reducing gas production efficiency and potentially leading to well shut-in. Plunger gas lift is widely used as an economical and effective deliquification technology; however, its overall performance is strongly governed by sealing behavior in the annular clearance between the plunger and tubing. Because the downhole environment is inaccessible and conventional monitoring techniques provide only indirect information, the actual motion characteristics of plungers and the associated dynamic gas–liquid sealing processes during lifting remain poorly understood. Consequently, reliable experimental evidence to elucidate sealing mechanisms and compare different plunger structures is still lacking. The objective of this study is to develop a visualized experimental platform for gas lift plunger sealing performance testing, to enable direct observation and quantitative characterization of plunger motion and gas-liquid distribution, to establish a comprehensive sealing performance evaluation method, and to provide experimental support for plunger structure optimization as well as experimental teaching and research training in oil and gas equipment engineering.

A full-scale visual experimental platform simulating a tubing–casing wellbore configuration was designed and constructed with an overall height of 11.0 m. Transparent tubing sections were used to enable direct visualization of plunger motion, liquid film development, and gas-liquid interface evolution throughout the lifting process. The platform integrates a gas supply system, liquid injection system, wellbore simulation system, safety protection system, and multiparameter measurement system. Compressed air is used to simulate formation gas supply, whereas a controllable water injection unit establishes different initial liquid loading conditions. High-speed imaging, displacement and velocity measurement units, and pressure sensors installed at the wellhead and bottomhole enable synchronous acquisition of plunger kinematics, pressure variations, and liquid production during each lifting cycle. Based on these measurements, a multidimensional sealing performance evaluation method is proposed by integrating pressure-loss characteristics and liquid leakage behavior. The average pressure loss during stable upward motion is used to characterize flow resistance induced by the sealing structure, whereas liquid leakage volume and liquid-carrying ratio are determined using a volumetric approach.

Visualized observations show that during plunger ascent, a liquid film forms in the annulus between the plunger outer surface and the tubing inner wall, while intermittent liquid backflow occurs due to the formation and rupture of leakage channels in the sealing zone. Distinct differences in gas-liquid interface morphology, leakage patterns, and flow stability are observed across plunger structures. Quantitative analysis shows that the rotary fishbone plunger consistently achieves a higher liquid-carrying ratio and a more stable pressure-loss response across a wide range of operating conditions than the solid fishbone plunger. In particular, under medium-to-low gas injection rates and relatively high liquid loading, the rotary fishbone plunger shows considerably enhanced liquid-lifting capability and a lower tendency for leakage. By contrast, the solid fishbone plunger is more prone to liquid backflow and exhibits larger fluctuations in pressure loss, especially under high liquid loading. These results indicate that plunger structural configuration plays a decisive role in sealing behavior.

A visualized experimental platform for testing gas-lift plunger sealing performance has been successfully developed, enabling direct observation of plunger motion and gas-liquid distribution, together with synchronous measurement of key operational parameters. A multi-index sealing performance evaluation method integrating pressure-loss characteristics and liquid leakage behavior has been established and experimentally validated. The results confirm that plunger structural configuration strongly influences sealing performance and liquid-lifting efficiency, and that the rotary fishbone plunger provides superior overall performance under most tested conditions. The proposed platform and evaluation methodology provide a reliable experimental foundation for plunger structure optimization and performance verification. In addition, the platform offers an effective tool for experimental teaching, graduate training, and research-oriented education in oil and gas equipment engineering and unconventional energy development.