摘要
鄂尔多斯盆地是我国大型聚煤盆地之一。侏罗、三叠、石炭二叠三大煤系在盆地内分布广泛,这些煤系地层有机质丰富,为油气的形成提供了雄厚的物质基础。本文以近年来的实验分析资料为依据,研究盆地北部石炭二叠系原油、天然气的组成及有机质的成分、类型和演化,讨论煤系地层油气形成的地球化学问题。
Abstract
In this paper, the problems of the generation of oil-gas in the Carboniferous-Permian coal-bearing strata of northern Ordos Basin are studied through the geochemical parameters of coal, mudstone, crude oil and natural gas, as well as the pyrolysis simulation test of coal. It is concluded that, (1) Terrestrial plant debris predominate in the abundant organic matter of the Carboniferous-Permian coal-bearing strata. The organic matter belongs to humuic type, containing much aromatic hydrocarbons and high pristane/phytane ratio offering low transformation efficiency and low potential for oil generation; (2) The natural gas and crude oil of Shihezi Formation are the products of the Carboniferous-Permian coal-bearing strata· In view of the carbon isotope fractionation occurred during the formation of gaseous molecules, the correlation between the isotopic and chemical compositions of reservoired gas and those of absorbed gas of coal bed is an effective method for identifying the source of thermogenic gas; (3) The formation of different combustible mineral products such as coal, petroleum and natural gas is in close connection with the composition of original organism possessing specialized chemical components. In coal series, the original organic matter is rich in lignin and cellulose, and the major pyrolytic products are gaseous hydrocarbons, while the potential of generating liguid hydrocarbons is limited. Therefore, the prospecting effort conducting in the Carboniferous-Permian coal-bearing strata of northern Ordos. Basin should be focussed on thermogenic gas.
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