Phenomena related to the storage of natural gas in underground caverns

This contribution reports on a preliminary study of various phenomena, that may occur during storage of natural gas in underground salt caverns. In these caverns the following substances are present: natural gas from different origins at pressures up to 300 bar, residual blanket (diesel oil), water and sodium chloride. In the caverns temperatures as high as 353 K have to be expected. Retrograde condensation may occur at pressure release, not only in the caverns, but also in the various operating facilities. The first part of this study focuses on the various aspects that govern the phase behavior inside the cavern. By means of well-chosen model systems representative for natural gas and diesel oil (octadecane), the main features of phase behavior have been studied. Also liquid dropout calculations were performed. Because natural gas is stored in the caverns for only a limited period, it is plausible that inside the caverns concentration and temperature gradients will be present, resulting in a variety of time-dependent processes. In the underlying study attention was also given to these aspects. Processes like molecular diffusion and free convection applied for simplified conditions have been studied, resulting in an insight how the dew point and liquid dropout may change in time.