Gas–liquid flowing process in a horizontal well with premature liquid loading

• Establish a visual gas–liquid flowing experimental apparatus for a horizontal well.
• Propose an experimental method to model the critical liquid loading conditions.
• Get the critical gas velocity of horizontal wells with premature liquid loading.
• Adopting a down-dip well trajectory benefits the liquid unloading.
• Opening toe-end formation improves the liquid unloading.

Horizontal wells are widely utilized as an important technique to improve the individual well producing rate. However, the actual production performance characteristics of a horizontal well in a reservoir demonstrate that the deliverability of several horizontal gas wells has not been developed effectively because of liquid loading. Understanding of this issue is confined to the production performance characteristics of the horizontal well because of the lack of techniques for the study of the liquid removal mechanism. To address this problem, an experimental device for the liquid removal mechanism of a visual-simulation horizontal well was established. Compared with the conventional conduit flow experimental device, the experimental device established in this study not only comprehensively considers the effect of the horizontal, bend, and vertical sections of the well but can also carry out the simulation under the conditions of different trajectories and intake locations. Through an in-depth analysis of the experimental phenomenon, two parameters, namely, water lock effect and reasonable velocity of liquid removal, were introduced to represent the liquid removal mechanism of the horizontal well under different conditions. Results indicate that the liquid lifting capability of the horizontal well is restricted by the producing energy. For a low-permeability sand reservoir with high water saturation, using a horizontal well with down-dip trajectory and opening the entire formation close to the toe are propitious for the removal of liquid in the horizontal well. These experimental results support the theory on trajectory optimization, opening the middle layer position optimization, reasonable proration, and improving the liquid removal result of the horizontal well in low-permeability sand gas reservoirs with high water saturation.