A depleted gas condensate reservoir in the Appalachian Basin was considered for Gas Storage. Upon completion of the primary production, a retrograde condensate is present in the reservoir. When depleted gas condensate reservoirs are used for gas storage, gas injection will pressurize the reservoir and will re-vaporize the condensate. As a result, the produced gas during withdrawal cycle will contain heavy hydrocarbons which need to be removed by processing units so the gas does not form liquid phases by retrograde condensation in pipeline.

Peng-Robinson Equation of State (PR-EOS) was utilized to predict the liquid yield during storage cycle. The first step in applying PR-EOS was to simulate the primary depletion and check against the reported primary condensate yields. Upon successful history matching the primary production, the remaining retrograde and residue gas were mixed with pipeline gas to pressurize the reservoir to its original pressure. The fluids were assumed to be completely mixed. Since the volume percent liquid in the reservoir at the end of primary depletion is 5-10%, gravity drainage of the hydrocarbon liquid may be minimized. However, it is possible that the liquid phase can potentially be wetting the pore walls. This may interfere with the mixing and revaporization process. PR-EOS was then used to predict the liquid yield for several separator pressures. In addition, several cases without complete mixing were considered to study the impact of mixing on liquid yield. The results were then utilized for design of surface facilities.

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