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In connection with the recent discovery of gas hydrates in Lake Baikal, numerous published materials, which could contain any information on the gas seepage from the bottom sediments, have been investigated. We revealed that in the 1930s, both direct and indirect data showing significant escapes of gases (presumably methane) in Lake Baikal were obtained. Analysis of these materials indicates that the dates of the ice steamthroughs opening are later and the intensity of gas escapes from the ice steamthroughs is lower at present as compared to the 1950s. The events of abundant death of pelagic fish golomyanka (Comephorus baicalensis Pall.) as well as specific forms of the ice cover caused by the methane escape, which used to happen in the lake, has not been recorded in Baikal since the 1950s. Thus, it seems that the intensity of gas escapes has significantly decreased for the last 50-60 years. This may be due to lowering of the number of catastrophic (M = 9-10) earthquakes in the Baikal region.

Natural gases emanating from the bottom of Baikal occur nearly ubiquitously along the shore, but their maximum concentration is observed at the front of the Selenga delta. In spring, the gas outputs are visible in the form of openings in the Baikal ice. Study was given to 54 openings. The gases are represented mainly by methane (75 vol.% on average), but highly nitrogenous types also occur (80 vol.% on average).
In addition to the explicit discharge of gases in the form of openings, the implicit discharge of gases exists throughout the Ust'-Selenga depression (USD). The chemical types of gases show areal zoning: from nitrogen on the piedmont periphery of the depression to methane in the near-shore band of the modern delta.
Joint analysis of geological, geophysical, and geochemical information proves that the USD sediment is a powerful source of generation of hydrocarbon gases and the similarity of its geologic structure with the South Caspian depression suggests the presence of "mud" volcanoes in Baikal.
A total of Cenozoic depressions of Baikal joint with its sedimentary bed is a potentially gas-bearing basin. Hydrocarbons are generated chiefly at the Baikal bottom, whereas the Selenga delta and other depressions are zones of their transit and accumulation. A regional cap for the natural reservoirs beneath the Baikal bottom may be a gas hydrate layer. Oil fields are hardly possible there, because all the studied gases are extremely dry and the bitumen contents in the USD sediments and grounds are very low. The reported facts and arguments permit the Baikal geology to be considered anew.

Geological, microbiological, and isotopic investigations showed that the bacterial communities form in surface sediments near a hydrothermal source in Frolikha Bay, northern Baikal. The base of these communities is colorless sulfur bacterium Thioploca. The bottom sediments in the region are characterized by intensive processes of sulfate reduction and methane genesis. Organic matter is used mostly for synthesis of methane. Carbon isotope composition in sediments and fauna (to -68.3 ) suggests that the metabolism of the community of bottom sediments of Frolikha Bay is based on biogenic methane utilized by methanotrophic bacteria. The intensity of methane oxidation reaches high values: 1180.4 L CH ₄/kgday.

Based on the concepts of occurrence of submarine gas hydrates as accumulations and on the general regularities of changes in their densities, global assessment of gas amount in gas hydrates of the World ocean is given. It is shown that the shape and the size of gas hydrate accumulations are controlled either by a concentrated flow of gas-containing fluids through the zone of gas hydrate stability and by parameters of their scattering halo or by a dissipated flow of gas-saturated water depending on fluid guides and lithologic peculiarities of the deposits. Geologo-geochemical and geophysical data on 10 best studied accumulations of gas hydrates were analyzed. The average specific (per unit area) content of gas in studied gas hydrate accumulation has been obtained, ca. 6.5108 m³/km². The specific gas content in gas hydrates within all potential gas-hydrate-bearing water areas is ca. 5106 m3/km2. According to data of performed mapping, the total area of these water areas is about 35.7 mln km², i.e., ca. 10% of the area of the World ocean. The total amount of gas, mainly methane, in the world's submarine gas hydrate accumulations is estimated at ca. 21014 m³.

Results of geological investigation of gas hydrate accumulation within the underwater sedimentary Blake Outer Ridge are presented. The study was based on both published and new data that we obtained by processing 164 and 172 ODP leg observations. The geological control over the distribution of gas hydrates is not quite clear despite the detailed seismic surveys and drilling within the study area. The geologic, tectonic, and hydro-geologic conditions in the Blake Outer Ridge area have been analyzed. A radically new technical approach was used: The gas hydrate accumulation was examined as a separate object with its specific characteristics. It has been proved that the investigated gas hydrates formed under the conditions of dissipated percolation of gas-containing fluids, which controlled the shape and the size of the accumulation. Based on geochemical, geophysical, and sedimentological data, the regularities of gas hydrate distribution within the Blake Outer Ridge have been established. The accumulation is controlled by tectonic factors, is of filtration origin, and occurs mainly in coarse-grained sediments.

The magnitude and spatial distribution of potential Black Sea methane hydrate reservoirs has been estimated on the basis of 6

There are massive quantities of gas hydrates in permafrost regions and deep-sea sediments. The current estimates show that the amount of energy in these gas hydrates is twice total fossil fuel reserves, indicating a huge source of energy, which can be exploited in the right economical conditions. Furthermore, these gas hydrates are a safety hazard to drilling operation, as they could become unstable under typical wellborn conditions and produce large quantities of gas. The decomposition of natural gas hydrates in porous media could also be responsible for subsea landslides and global weather changes. Recent studies show that they might provide an opportunity for CO₂ sequestering.
Hydrate phase boundary in porous media is known to be a function of many factors, such as pore size, fluid saturation, in situ stresses, and sediment mineralogy. Deviations, as great as 100 m, have been observed between the measured and predicted thickness of hydrate stability zones in marine sediments. Laboratory efforts in measuring gas hydrate stability zone in porous media have concentrated on the effect of pore size and fluid saturation. However, there are considerable deviations and inconsistencies in the reported data.
This paper presents an experimental setup, test procedures, and some of the results obtained on porous glass beads with 306 and 158 pore sizes with using methane and CO₂. The test procedure is based on stepwise heating as compared to continuous heating used by many laboratories. The results proved that stepwise heating technique could provide reliable and consistent data on measuring hydrate phase boundary in porous media, without compromising on the time and cost of experiments. The data showed that there could be a significant difference between the hydrate free zone of gas hydrates in porous media and that of bulk conditions. These results are important in estimating the hydrate stability zones in porous media, as indicated by BSR in seismic surveys.

We have experimentally studied the peculiarities of water-gas hydrate and water-ice phase transitions under gas pressure in dispersed methane-saturated grounds on cyclic cooling-heating. Data on the conditions of hydrate and ice formation in the ground pores have been obtained. It is shown that on cooling of dispersed rocks, only part of the pore water passes into hydrates; the rest (intimately bound with the particle surface) transforms into ice on further cooling. Hydrate formation in the studied grounds, compared with the system pure water-gas, occurs at higher pressures and lower temperatures. It is demonstrated that the ground dispersion and cooling-heating cycles affect the PT-conditions of formation and decomposition of gas hydrates. Petrography of frozen artificially hydrate-saturated rocks is studied.

Over 200 sites of exhalation (95-98% methane) have been discovered through the past 15 years in the northwestern Black Sea. Fields of exhalation are most often attributed to large fault zones. Many sites are associated with carbonates.

Most typical examples of gas saturation images in acoustic fields are presented based on data obtained using a MAK-1M acoustic complex (designed at 'Yuzhmorgeologiya' Science Center) during research trips in the Black Sea and north-western Pacific.