Numerical and analytical modeling of the gas-well liquid-loading process

Liquid loading is a serious problem in areas where gas fields are maturing. This paper presents an analysis of the production behavior of liquid-loaded wells over time. This clearly shows that these wells can operate at two different rates-a stable rate, at which full production is taking place, and at a lower metastable rate, at which liquid-loading effects play a role. A model has been constructed that enhances the understanding of the process of water buildup and drainage in gas wells. It assumes a single gas- and water-coproduction point and a single water reinjection point. As expected, a water column is built up in the well as soon as production takes place below the critical rate. As observed in the field, for good inflow performance, a metastable flow rate can be observed. At this state, the water-reinjection and water-coproduction rate are equal to one another, and the water-column height stabilizes. A sensitivity analysis has been carried out to determine how well parameters influence the metastable flow rate, the time required to reach this metastable rate, the corresponding water-column height, and the shut-in time required to drain this water column. The results of the analysis indicate that significant metastable flow rates occur in wells that have good inflow performance a low water/gas ratio, and a large distance between injection and production point. Furthermore, a steady-state analytical solution has been derived for the metastable rate and stabilized water-column height confirming the numerical-analysis results.