EXPERIMENTAL EVIDENCE OF THE GENERATION OF OIL-GAS IN PERMOCARBONIFEROUS COAL-BEARING STRATA OF NORTHERN ORDOS BASIN

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.