CHARACTERISTICS OF ISOTOPE COMPOSITION OF GASIFORM HYDROCARBON AND IDENTIFICATION OF COAL-TYPE GAS

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     

气态烃同位素组成特征及煤型气判识

本文以烃类气体的碳、氢同位素组成为主,探讨了煤型气、油型气的判识。文中综合利用甲烷碳、氢同位素组成,把我国不同地区的天然气较好地分为几个区间,即生物气、瓦斯气、油型气和煤型气。在煤型气和油型气之间有一个混合气区,有较为复杂的形成条件,过成熟的油型气在分布上与煤型气重叠。根据对我国四川、鄂尔多斯油气区的研究,认为这些盆地的煤型气具有相对较轻的碳同位素组成,其δ~(13)C_1与R_0的数学表达式δ~(13)C_1‰=8.641,lgR_0—32.8。它代表一种连续沉降盆内形成的煤型气模式。本文还探讨了中原油田最近发现的深层气(大于4000m)的母质类型,有机相和成熟度。