A depleted gas condensate reservoir in the Appalachian Basin has been under investigation for possible conversion to a gas storage reservoir. When depleted gas condensate reservoirs are used for gas storage, the injected gas will pressurize the reservoir and will evaporate the retrograde condensate that is remaining in the reservoir upon completion of the primary production. This will result in significant compositional alteration of the withdrawn gas from the storage. The produced gas during withdrawal cycle must be processed to remove condensible hydrocarbons prior to pipeline transportation to prevent liquid drop out by retrograde condensation in the pipeline. The composition of produced gas will depend on the degree of mixing between the injected and the residue fluids.

To investigate the impact of the formation on the mixing, a compositional reservoir simulator was utilized in this study. The primary production history of the reservoir was first modeled with simulator using available data and the results of the data analysis. The phase behavior studies with Peng-Robinson equation of state (PR-EOS) provided a reliable estimate for reservoir fluid composition. Upon successfully history matching the primary production, the reservoir model was utilized to predict the composition of the withdrawn gas from the storage. Pipeline gas was injected into the reservoir and the reservoir was pressurized to its original pressure. Both vertical and horizontal wells were considered for injection to evaluate the extent of mixing among residue gas, residue condensate, and the injected gas. Subsequently, a withdrawal cycle was simulated to predict the liquid yields and gas heating contents based on the design of the surface facilities. The results of simulation study were then used to finalize the design storage field and surface facilities. The preliminary data collected after pressurizing the reservoir confirms the simulation results.

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