A pragmatic approach to understanding liquid loading in gas wells
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Copyright 2014, Society of Petroleum Engineers. Liquid loading is the inability of a producing gas well to remove its coproduced liquids from the wellbore. The liquid flowing as droplets or film accumulates at the well bottom, thereby imposing backpressure at the sandface and triggering increasingly higher pressure loss in the wellbore. The problem initiated by liquid loading is manifested in terms of loss in well deliverability, causing the wellhead pressure (WHP) to decline significantly, which, in turn, leads to the cessation of gas production. Accordingly, the liquid-loading issue reduces the ultimate recovery of a gas well. Both the droplet-flow reversal and liquid-film-flow reversal have been postulated to be the underlying mechanism for liquid loading. Both mechanisms are predominantly premised on diagnosing the problem at the wellhead flow conditions. This study explores the deliquefication issue in a gas well by fluid and heat flow modeling of the entire wellbore for a variety of flow situations in gas and gas/condensate reservoirs. We observed that when a well experiences annular two-phase flow throughout the wellbore, no liquid loading occurs. The transition from annular to churn or slug flow initiates the liquid-film-flow or droplet-flow reversal, thereby triggering liquid loading. Most often the flow condition at the well bottom controls the onset of liquid loading. Using three published datasets, we showed that the understanding of liquid loading improved when the entire wellbore flow modeling was used. Forward modeling suggested that the tubing inside diameter (ID) and the well productivity index (PI) are the most important independent variables in determining the critical liquid loading rate and the onset of liquid loading.