Abstract
During gas hydrate formation process, a phase transition of liquid water exists naturally, implying that temperature has an important influence on hydrate formation. In this study, methane hydrate was formed within the same media. The experimental system was kept at 1.45, 6.49, and 12.91 °C respectively, and then different pressurization modes were applied in steps. We proposed a new indicator, namely the slope of the gas flow rates against time (dνg/dt), to represent the intrinsic driving force for hydrate formation. The driving force was calculated as a fixed value at the different stages of formation, including initial nucleation/growth, secondary nucleation/growth, and decay. The amounts of gas consumed at each stage were also calculated. The results show that the driving force during each stage follows an inverse relation with temperature, whereas the amount of consumed gas is proportional to temperature. This opposite trend indicates that the influences of temperature on the specific formation processes and final amounts of gas contained in hydrate should be considered separately. Our results also suggest that the specific ambient temperature under which hydrate is formed should be taken into consideration, when explaining the formation of different configurations and saturations of gas hydrates in natural reservoirs.
Highlights
During gas hydrate formation process, a phase transition of liquid water exists naturally, implying that temperature has an important influence on hydrate formation
Because hydrate was formed spontaneously under constant pressure and temperature conditions, changes in the measured time-dependent curves of temperature and gas flow rate indicate the different stages of hydrate formation
Methane hydrate was formed with the pressurization method, in which methane gas was pressurized to certain values with different modes and the methane gas was constantly supplied by an automatic gas pump
Summary
During gas hydrate formation process, a phase transition of liquid water exists naturally, implying that temperature has an important influence on hydrate formation. The results show that the driving force during each stage follows an inverse relation with temperature, whereas the amount of consumed gas is proportional to temperature This opposite trend indicates that the influences of temperature on the specific formation processes and final amounts of gas contained in hydrate should be considered separately. Our results suggest that the specific ambient temperature under which hydrate is formed should be taken into consideration, when explaining the formation of different configurations and saturations of gas hydrates in natural reservoirs. Three– phase equilibrium conditions over different temperatures and pressures for different types of hydrates have been successfully established[27] Based on these findings, sub-cooling or overpressure relative to the equilibrium conditions have been considered as the sole standard for determining the driving force for hydrate formation. Using molecular dynamics (MD) simulations, it was confirmed that guest www.nature.com/scientificreports/
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