Underground Natural Gas Storage in a Low Quality Gas Reservoir - Produced Gas Quality Control by Rate Optimization

Abstract

Due to increasing demand for natural gas, storage plan development in order to cope with seasonal gas fluctuations and ensure constant gas supply during a year, has recently become highly indispensable. However, developing underground gas storage (UGS) facility is so costly which may sometimes discourage the investment.One of the main cost items while fulfilling a UGS project can be attributed to cushion gas; this is part of gas inventory which remainspermanently in the storage field in order to maintain pressure and provide adequate deliverability rate during production cycles.For this reason, UGS in low quality gas reservoirs has been recentlyproposed. In such a case, native reservoir gas would be used as cushion and it will greatly improve economic feasibility of UGS plan. Nevertheless, the possible mixing between natural gas and reservoir low quality gas may jeopardizethe quality of production stream. This paper simulates natural gas storage in a real low quality gas reservoir comprising 85% nitrogen. The purpose of modelling is to offer an optimized storage plan (by using the best injection/production scenario) whichguarantees the quality of withdrawal gas for at least 5 successive production cycles, whilst producing with the maximum possible deliverability rate.