A Study on Effects of Initial Injection Period, Dispersion, and Diffusion Phenomena on Mixing of Base and Working gas during Natural Gas Storage in a Nitrogen Reservoir

Due to the growing consumption of natural gas in the world, underground natural gas storage (UGS), as a way to cope with the imbalance of gas supply and demand especially during cold seasons, seems to be really indispensable. The largest part of investment in a UGS plan development is allocated to providing cushion gas; this gas is required to maintain reservoir pressure during withdrawal cycles and insure adequate deliverability rate. Since economic evaluation of gas storage projects is of great significance, recently implementing UGS in low quality gas reservoirs such as nitrogen reservoirs has become highlighted. In such a case, reservoir low quality gas will be used as cushion and not only it leads to a higher production rate but also it considerably reduces the cost of preparing and injecting cushion gas into the reservoir. However, there may be a problem related to mixing between reservoir low quality gas and natural injecting gas; this phenomenon shall be effectively controlled by choosing the suitable production strategy. This study investigates underground natural gas storage in an abandoned gas reservoir which mainly consists of nitrogen (%85 Nitrogen). The effect of initial injection period and therefore total injection volume around the well, as well as the factors affecting the extent of mixing between reservoir’s low quality gas and injected natural gas in molecular scale such as diffusion and dispersion will be investigated.