This paper presents the results of an investigation of the design of production tubing string setting depths in gas wells to optimize gas recovery in wells that produce free liquids in conjunction with the gas. Particularly important in this work has been the evaluation of the conditions for which the well outflow velocity is less than that which would be required to continuously transport and unload liquids from the well. Sub-critical velocities are often encountered in low productivity gas wells that produce liquids, whether the wellbore liquids are produced directly from the formation and/or condensed from the gas in the wellbore. The produced liquids considered in the analysis can be water and/or liquid hydrocarbons.

This paper presents an optimization technique for determining the most efficient production tubing string setting depth design that will keep the wellbore continuously unloaded of produced liquids, yet result in the maximum gas recovery possible under those conditions. The optimization can be performed for a single completion operation during the productive life of the well, or for a series of periodic well interventions during the productive life of the well for which the tubing string setting depths are selected.

The wellbore liquid-loading mechanism in a sub-critical velocity production system has been considered in the analysis using a mechanistic wellbore outflow model. A commingled reservoir inflow performance model was utilized in the analysis to evaluate the fluid inflow of multilayer gas reservoirs that may produce liquids in conjunction with the gas.

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