Experimental and Transient Simulation of Dynamic Liquid Loading Phenomenon in Ultra-Deep Gas Wells

During the production of ultra-deep gas wells, a retained oscillating liquid column may form in the wellbore, leading to inaccurate predictions of liquid loading. This phenomenon is referred to as dynamic liquid loading. To investigate the identification and formation mechanism of this phenomenon, a systematic study was carried out using visualized gas-liquid two-phase flow physical experiments and OLGA transient multiphase flow simulations, aiming to provide new theoretical support for addressing liquid loading issues in ultra-deep gas wells. The results successfully reproduced the phenomenon in which a liquid column oscillates up and down within the wellbore without causing well shutdown, indicating that the essence of the dynamic liquid-carrying phenomenon is the reciprocating motion of a liquid column inside the wellbore. Under certain gas–liquid ratio and well depth conditions, the gas well can remain in stable operation even at gas velocities below the conventional critical liquid-carrying threshold. Experimental results show that when the in-situ gas–liquid ratio falls below 50 m³/m³, the liquid-carrying capacity is greatly reduced, while higher ratios within a certain range intensify the dynamic liquid-carrying phenomenon. Extrapolation using the Euler similarity criterion identified the maximum and minimum gas–liquid ratios and the critical well depth for its occurrence. The dynamic liquid-carrying phenomenon reveals the conditions under which ultra-deep gas wells can maintain stable production at gas velocities below the critical gas velocity. It provides a basis for determining the appropriate timing of artificial lift intervention, optimizing drainage gas recovery parameters, and enhancing production efficiency.