Phase state of hydrocarbon agglomerations in subsoil of Western Arctic seabed
The main prospects for discoveries of new free gas and oil fields and increments of hydrocarbon reserves relate to the sedimentary basins of Northern Eurasia (Russian lands and Arctic and Far-Eastern waters). The biggest megabasins at Western Arctic region are the basin of Barents Sea and the Southern-Kara region of Western Siberia, as well as the northern offshore part of Timan-Pechora province. In total, there are 35 offshore fields in Western Arctic including the offshore-onshore ones. Their aggregated gas reserves of А+В1+С1+С2 categories exceed 10,3∙1012 m3.Estimations of oil and gas presence in Barents and Southern-Kara regions of Western-Siberian megaprovince,and forecast of the phase state of hydrocarbon deposits and their distribution in a sedimentary basin either in section, or in area are based on analysis of types of the organic matter and its katagenetic maturation in a source rock interval, as well as on peculiarities of tectonic structure and evolution of the basin, which determine modus operandi of vertical and lateral migration, accumulation and preservation of hydrocarbons.Taking into account generation ability of the organic matter in a studied Jurassic-Triassic part of the sedimentary apron, and existence of the discovered gas and gas-condensate fields within the margins of Southern-Barents depression and Shtockman-Luddlovskaya saddle, the presence of oil agglomerations is probable in the traps at the western border of Barents megadownfold. A zone where gas and gas-condensate fields have formed in Barents megadownfold is associated with the central parts of Southern and Northern Barents depressions and the downfold of Saint Anna. The new major discoveries of heavy sapropelic immature oil are possible only in Pechora Sea, and at Prirazlomnoye and Dolginskoye fields.According to the Gazprom VNIIGAZ LLC, the calculated amounts of gas resources in Kara Sea together with its gulfs equal 21∙1012 m3, oil resources equal (2,1…2,6)∙109 t / (0,8…1,0)∙109 t (geological/recoverable). Regarding the phase state of offshore hydrocarbons there will be mostly gas-condensate fields, less often gas fields (with deposits only in the Aptian-Cenomanian part of the section), even less often - gas-condensate-oil fields, and very rarely oil-gas-condensate fields. At that, existence of purely oil deposits and fields seems genetically impossible. The probable locations for oil agglomerations in the form of sub-gas oil rims having various sizes and thicknesses are the external areas of the Southern-Kara offshore region.