Methane hydrate formation in excess water simulating marine locations and the impact of thermal stimulation on energy recovery

In this work, we investigated the gas and water production profiles from methane hydrates formed in an excess water environment that mimic marine locations. Instead of pressurization by the addition of gas, water was injected into the sediment to create the high pressure environment of the reservoir, thereby creating a hydrate bearing sediment of high water saturation similar to those in marine locations. A framework is introduced to determine fractions of methane converted into hydrates during hydrate formation stage taking into account the effect of density changes, solubility and the in-situ pressure and temperature conditions. As opposed to 100% conversion assumed in the previous excess water works, our quantification shows that on average, the fractional conversion of methane is around 81.5% at comparable or larger experimental time scales (76–408h). Upon the formation of quantitatively similar hydrate bearing sediments, the dissociation of methane hydrate was done under a constant pressure of 4.5MPa subjecting to different thermal stimulation extents from 278.7K to 285.2K. It was found that low temperature driving force would result in an extremely low dissociation rate, and a minimum temperature of 280.7K (corresponding to 2.1K temperature driving force) is required to achieve a 90% dissociation within 10h. In addition, through a simplified estimation of energy efficiency ratio (EER) and analysis of water production profile, we demonstrated the importance of water management in developing methods to effectively recover energy from hydrate bearing sediments.