ИСТИНА

Gas hydrates in permafrost can occur in under-permafrost and intra-permafrost horizons. The intra-permafrost hydrates repeatedly recorded during deep drilling operations in cold regions. Different indirect indicators show that hydrates can locate in shallow permafrost (up to depth 200 m) under non-equilibrium conditions in a metastable state due to self-preservation effect. The relict hydrates may be responsible for methane emission and gas explosion hazard in shallow permafrost during drilling and production in gas fields of northern West Siberia. The metastable hydrates are extremely sensitive to various influences (including anthropogenic impact) and create serious geologic risks to oil and gas exploration and development and need special study. The physical (thermal and filtration) properties of frozen sediments with self-preserved gas hydrates should be investigated. The experimental results show that gas permeability and thermal conductivity of frozen hydrate-bearing sediments may change by several times during the self-preservation effect, and correlates with pore ice and hydrate ratio.