PHASE BOUNDARY EQUILIBRIUM CONDITIONS FOR CH4, C2H6 AND C3H8 IN MARINE QUARTZ-BASED POROUS SAND: THERMODYNAMIC EVOLUTION OF THE SYSTEM AND DEVIATION FROM THE IDEAL TREND

Natural gas hydrate reservoirs often consist of a mixture of various gaseous species: small-chain hydrocarbons, as methane, ethane, propane and butane, and other species, as carbon dioxide, nitrogen, oxygen, hydrogen sulfide and others. Every species shows different forming conditions. Moreover, those conditions may change as a function of the mixture composition and the properties of the surrounding environment. The present study deals the production of hydrates with small-chain hydrocarbons, within a silica-based porous marine sediment. Hydrates were formed and melted, the experimental phase boundary equilibrium conditions were then compared with the ideal ones, obtained from literature. Such a comparison allowed to characterize how the sediment acted during the process. In presence of methane and ethane, It was found capable to promote the process, while It acted as inhibitor for propane hydrates. The difference observed between the various species, were finally explained in terms of typology of hydrate structure formed and molecular diameter of the guest species.