| 摘 要： | The natural gas which forms in the course of the formation of coal in the coal-series stra-ta is called the coal-type gas. It is an important genetic type of combustible gas. This papertakes the isotope composition of carbon and hydrogen as a key factor to make an approachto the identification of the coal-type gas and the oil-type gas. According to the isotope com-position of methane carbon and hydrogen, we have divided the natural gases in differentplaces into biogas, coal gas, oil-type gas and coal-type gas. There is a mixed gas area bet-ween the coal-type gas and the oil-type gas. The conditions for the formation of the areaare comparatively complex. The overmature oil-type gas overlies the coal-type gas in distri-bution. According to our studies on oil-gas areas in the Sichuan basin and Eerdos basin,we come to know that the coal-type gas in these basins has an isotope composition of highercarbon. Its mathematic expression of δ~(13)C_1-R_0 is δ~(13)C_1‰ = 8.641 lgR_0-32. 8, representing a mod-el o
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