A local drift-flux closure for gas-liquid countercurrent flow in the extremely narrow annulus of plunger lift

Abstract During plunger lift, gas bypass and liquid fallback may coexist in the extremely narrow annulus between the plunger and tubing, forming a local gas–liquid countercurrent flow affected by confinement, moving-boundary shear, and interfacial slip. Conventional drift-flux closures may therefore have limited transferability. In this study, 59 vertical air–water experiments were used to reconstruct the equivalent distribution parameter C0 and drift velocity Vd for this local flow region. The transferability of four representative correlations—Zuber–Findlay, Gomez, Bhagwat–Ghajar, and Liu—was first evaluated. A stepwise inverse-calculation strategy was then adopted to identify the dominant variable of C0 before reconstructing Vd using the recommended C0. Results show that the existing correlations generally overpredict gas holdup. The reconstructed C0 is mainly governed by gas holdup αg, whereas the plunger velocity ratio Πp provides only a secondary correction. In contrast, Πp gives a more stable correction to the dimensionless drift velocity Y, indicating that plunger motion mainly modifies gas–liquid relative slip rather than cross-sectional distribution. For the present database, the reconstructed closure yielded MAPEs of 0.676% in back-substitution validation and 24.762% in implicit forward prediction, which were lower than those of the tested correlations. The proposed closure supports gas-holdup estimation, plunger leakage analysis, and local bypass-flow evaluation under fixed-geometry, vertical, laboratory air–pure-water, extremely narrow annular countercurrent-flow conditions, and should not be regarded as a general correlation for all downhole gas–liquid systems.