Possibilities of Gas-Hydrates Formation in the Western Arctic Shelf of Russia

Submarine gas hydrates are ice-like solid structures form from pore water and natural gases [Brooks, J.M., Barnard L.A., Wiesenburg D.A., M.C. Kennucutt II, and Kvenvolden K.A., 1983. Molecular and isotopic compositions of hydrocarbons at site 533, Deep-Sea Drilling Project, Leg 76 // In Init. Repts. DSDP, 76, edited by Sheridan R.E., Gradstein F.M and the leg 76 Science Party, pp. 377-389 (U.S. Govt. Printing Office), Washington.], under special conditions of relatively low temperature and high pressure. In nature methane hydrates occur in seafloor sediments of various regions of the World Ocean [Kvenvolden K.A., Ginsburg G.D. and Soloviev V.A., 1993, Worldwide distribution of subaquatic gas hydrates. Geo-Marine Letters, 13: 32-40; Ginsburg G.D. and Soloviev V.A., 1994, Submarine gas hydrates (in Russian), VNIIOkeanologiya, St.Petersburg, 199 p.] as well as in permafrost environment [Soloviev, V. A., Ginsburg G.D., Telepnev E.V., Michalyuk Yu.N. Kriogeotermiya i gidraty rirodnogo raza v nedrach Severnogo Ledovitogo OKeana, L.: PGO "Sevmorgeologiya", 1987, 150 s.]. The main object of th is stu dy is submarine gas hydrates of Arctic region. The main goal of this work is determination of the possibilities of the gas hydrate formation on the Western Arctic Shelf of Russia. Nevertheless a short overview of the gas hydrate manifestations in the World Ocean is given in separate chapter for reference. The geological structure of the Barents - Kara Shelves and the distribution of the hydrocarbons are described. The work also presents the analysis of the theoretical conditions of gas hydrate formation from the pure methane and a mixture with impurities. This study h a s defined possible gas hydrate distribution for the regional mapping where the seafloor methane hydrates would be stable. After the prediction using Software package (by Sloan) the mapping was carried out in a Geographical Information System (GIS) environment. The bottom temperature of the study area (Barents-Kara Shelves) is a key data for the prediction. The equilibrium pressure and suitable depth (Table 1) as a result of the prediction was defined (2500-4400 kPa) at an average salinity of 34,38%o. The average geothermal gradient of both the Barents and Kara Seas is around 2,8 °C/100 m [Zakharov E.V., Kulibakina I.B., 1997. Geothermal regime of the subsurbace - one of the main factors governing an extent of prospects of oil and gasbearing basins // Oil and gas geology. [Online] From URL: http://geolib.ru/OilGasGeo/1997/12/Stat/stat04.html#table] which was taken for the calculation of the gas hydrate stability zone (GHSZ) thickness. The area of the possible gas hydrate distribution in the Western Arctic Shelf of Russia according to re su lts of this computation achieves 2,3*10h11 m2 or 230905 km2. The biggest a rea of the possible gas hydrate manifestation of 122629 sqare km (more than an half of all area) situ ated between the Barents and Kara Seas on the St. Anna Trough (Svyataya Anna Trough) which located to south-east of Franz Josef Land, under the 620 m water depth. The thicknesses of the gas hydrate stability zone were estimated for each area as well. It varies from 71 m below the seafloor at the high bottom temperatures (+2 - +4°C) in the Western Barents Sea near Medvezhiy Island to 306 m below the seafloor at the coldest bottom temperature (-1,75 °C) in the southeastern coast of Novaya Zemlya Islands in the Kara Sea (Matochkin Shar). Also a total volume of the feasible gas hydrates was calculated in (5-8)*10h11 m3 or (5-8)*10h5 km3 at hydrate occupancy of the Sediments of 0,9-1,5% and hydrate occupancy of pore space in the sediments of 3-5% considering an average porosity (30%) of the sediments