HR: 0800h
AN: C11A-1059    [Abstracts]
TI: The peculiarities of relict gas hydrate forms existence within permafrost layers
AU: * Chuvilin, E
EM: chuvilin@geol.msu.ru
AF: Chuvilin, Faculty of Geology, MSU, Vorobjevy Gory, Moscow, 199899 Russian Federation
AB: It's well known that permafrost zone of the Earth is favorable for formation and existence of such ice-like compounds as gas (mainly methane) hydrates. Currently methane hydrate accumulations have identified either by direct evidences (hydrate-containing core sample) or indirect evidences in various permafrost regions of the world (Arctic coast of Canada, Alaska, the North of Siberia etc.). The special interest excites the fact that gas hydrate-shows (indirect evidences) are documented for shallow depths (down to 200-300 m) above the gas hydrate stability zone (GHSZ). The north-west part of Yamal ( West Siberia) is one of such areas (Chuvilin et al.,1998, Yakushev and Chuvilin, 2000). Special research, which included analysis of monitoring wells in cryolithozone, as well research of permafrost cores recovered during drilling, can be assumed that at least a part of gas in similar intrapermafrost accumulations exist in the form of metastable (relict) gas hydrates. They were formed in the past and exist now to the self-preservation effect. Some models of gas hydrate formation in shallow depths in permafrost are possible. They can associate with sea transgression, regional ice cover formation, freezing of gas saturated talik zones, permafrost sediments formation etc. After pressure reduction, hydrate passed through the self-preservation stage remained metastable for a long time. However, according to the shallow depth and metastable condition self reserved gas hydrate have tendency to dissociate due to the global climate warming, as well as to different technogenic effects such drilling and mining. Possibilities of formation metastable gas hydrate in permafrost confirm the special experimental investigation of gas hydrate accumulation in freezing sediments (Chuvilin and Kozlova, 2004). The experimental data shows, that the cooling of gas hydrate saturated sediments to negative temperature induced ice formation. Enclosing hydrate ice would originate from the remaining bulk water and interfacial water located on the particles and aggregates surface. The primary hydrate preservation will occur by surrounding ice. Under thermodynamic non-equilibrium condition for hydrate existence (pressure reducing to atmosphere level) secondary preservation of pore hydrate would be occurred due to partially hydrate dissociation. This phenomenon was described earlier as self- preservation effect at negative temperature. The results of quantitative experimental study of frozen hydrate-saturated sediments metastability showed that self preservation effect of gas hydrate in pore space od sediments was determined by complex of hydrate containing sediments parameters and characteristics, some among them should be mentioned, such as: temperature conditions, macro- and micromorphological features, degree of hydrate and ice pore space filling, composition and properties of sediment matrix etc. Obtained experimental data make possible to substantiation of relic gas hydrate forms existence within permafrost layers. These investigations were supported by grants INTAS Nr03-51-4259 and RFBR Nr04-05-64757.
DE: 0702 Permafrost (0475)
DE: 0714 Clathrate
DE: 0738 Ice (1863)
DE: 0766 Thermodynamics (1011, 3611, 8411)
SC: Cryosphere [C]
MN: Fall Meeting 2005