Investigation on excess gas method for synthesis of methane gas hydrates

The methodologies generally adopted for synthesis of methane hydrates (e.g., the dissolved gas method, excess gas method and the ice seeding method) signifies the importance of appropriate thermodynamic conditions for the dissolution characteristics of methane in water and its subsequent crystallization to form hydrates. The 'dissolved gas method' and 'excess gas method', which mimics the natural formation and existence of methane hydrates beneath ocean bed, can be employed for controlled synthesis of hydrates by regulating the pressure and temperature. However, explicit research has not yet been conducted to understand the rate of temperature decrease in methane dissolution characteristics, prior to gas hydrate formation. At a definite pressure-temperature condition, the dissolution characteristics are largely dependent on the 'interaction time', or 'contact time', available for methane gas to dissolute in water. Therefore, an investigation was conducted to (i) ascertain the rate of hydrate formation, (ii) quantify the volume of gas hydrates formed, corresponding to different combinations of pressure and temperature, and (iii) to understand the impact of memory effect, in a closed cell. This study demonstrates that though the stability of gas hydrates is principally dependent on the pressure and temperature combinations, sufficient interaction time should be provided for their stable occurrence. Moreover, it was also proven that the relevance of memory effect was predominant after the fifth run of hydrate formation-dissociation cycle.