Liquid holdup correlation for conditions affected by partial flow reversal

A new method to predict liquid holdup in vertical upward gas-liquid flows is presented based on large scale steady-state experiments in a transparent 42-m long, 0.048-m ID vertical tube system. This work focuses on situations of particular significance in natural gas producing wells, when annular to churn flow-pattern transition brings about drastic holdup increase, leading to a rich group of phenomena in the field, known as “liquid loading”. Under circumstances, believed to precede liquid loading, the still steady-state and stable liquid holdup may be several folds larger than the inlet volumetric fraction of the liquid, due to partial flow reversal. Standard two-phase correlations have difficulties in reproducing the observations in such situations. The proposed method is actually flow-pattern independent and relies on a measure of nearness of the flow condition to the specific condition when partial flow reversal starts to appear. Interestingly, the actual form of this correlation is quite simple, relying on the gas and liquid superficial velocities and mass fractions - in addition to the key parameter - the “critical” superficial gas velocity.