Gas Well Performance at Subcritical Rates

摘要

Gas wells producing late in their life are normally subject toliquid loading problems. As rates fall below the critical ratenecessary for unloading, a static liquid column will oftendevelop in the well. This can result from condensed water outof the gas phase or formation water being produced into a wellhaving insufficient gas velocity to clear the liquid from thewellbore. The presence of this liquid column impairs the wellperformance by imparting additional back pressure on thereservoir. The water saturation around the wellbore canincrease causing a reduction in the near well effective gaspermeability which further compounds the problem of keepingthe well unloaded. Traditional methods of evaluating wellperformance do not properly capture this phenomena;therefore, the existence of additional back pressure on thereservoir can go undetected. Wells continue to produce, but ata reduced rate because of the liquid column. Numerousanalysis techniques are available to model static liquidcolumns in wellbores. A review of these methods and anevaluation of these techniques is presented. Comparisons withfield data are made to ascertain the accuracy of the methodsand to select an appropriate method to model wellperformance. Incorporation of this method into a well designallows for the optimization of well productivity.