(515i) Transient Hydrate Formation/Dissociation of Methane Hydrates in Porous Media At Hydrate Stable Conditions

Natural gas hydrates are crystalline compounds formed from mixtures of water and methane or other gases at sufficiently high pressures and low temperatures. They are considered a potential unconventional energy resource. It is estimated that the liberation and subsequent production of just 15% of the trapped gas in hydrates would provide the world with energy for 200 years at the current level of energy consumption. Understanding the fundamental behavior of hydrate formation and dissociation in porous media is necessary in order to avoid the potential hazards during production from the hydrate reservoirs in the marine sediments and permafrost regions. In this study, methane hydrate formation and dissociation in porous media was observed. Experiments were carried out at 8.0 MPa, 274.15 K and different water saturation levels (50 and 100%). Two types of porous media (silica sand and activated carbon) were employed. In silica sand bed, hydrate crystals were observed to form in the inter-particle pore space and a stable and clear hydrate front movement across the crystallizer was observed. On the other hand, nucleation of hydrate crystals on the surface of the activated carbon grain and then dissociation in the hydrate stable region was observed in activated carbon bed. This occurrence of hydrate formation and dissociation processes within the hydrate stability region is defined as transient hydrate formation/dissociation. Based on our results, we postulated that particle size, pore space and water saturation level might play a role in transient hydrate formation/dissociation. When a smaller sized activated carbon grains were used, a clear and stable hydrate front was observed. Our results suggests that pore space and its interconnectivity plays an important role in hydrate formation in porous media.