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烷烃气碳同位素系列类型有3种:随烷烃气分子碳数递增,δ13 C值依次递增称为正碳同位素系列,是有机成因原生烷烃气的一个特征;随烷烃气分子碳数递增,δ13 C值依次递减称为负碳同位素系列;不按以上2种规律而出现不规则增减则称为碳同位素倒转。负碳同位素系列又分为原生型和次生型2种。原生型负碳同位素系列是无机成因的;次生型负碳同位素系列是正碳同位素系列经次生改造来的,出现在过成熟的页岩气和煤成气中。关于次生型负碳同位素系列成因的观点繁多,包括:二次裂解、扩散、过渡金属和水介质在250~300℃范围内发生氧化还原作用导致乙烷和丙烷瑞利分馏等。详细研究对比后发现不论页岩气或者煤成气,次生型负碳同位素系列仅出现在过成熟页岩或源岩区,在成熟和高成熟页岩或者源岩区未见次生型负碳同位素系列,由此得出过成熟或者高温(>200℃)是次生型负碳同位素系列的主要控制因素,在此主控因素下可由二次裂解、扩散或者乙烷和丙烷瑞利分馏的一种或几种方式促使次生型负碳同位素系列的形成。
There are three types of alkane gas carbon isotopes: With the increase of molecular carbon number of alkane gas, δ13C values are successively called positive carbon isotope series, which is a characteristic of organic origin alkane gas. With the increase of molecular carbon of alkane gas, δ13C Decreased values are called negative carbon isotope series; not according to the above two kinds of rules appear irregular increase or decrease is called carbon isotope inversion. Negative carbon isotope series is divided into two types of primary and secondary. The primary negative carbon isotope series is of inorganic origin; the secondary negative carbon isotope series is a series of positive carbon isotopes that were secondarily remodeled in over-mature shale gas and coal-to-coal gas. There are many opinions on the origin of the secondary negative carbon isotope series, including secondary cracking, diffusion, oxidation and reduction of transition metals and aqueous media at 250-300 ° C, leading to fractionation of ethane and propane Rayleigh. After a detailed study and comparison, it was found that secondary shale negative carbon isotope series occur only in over-mature shale or source rock areas, regardless of shale gas or coal gas, and no secondary negative in mature and highly mature shale or source rock areas Carbon isotope series, which concluded that overripening or high temperature (> 200 ℃) is the main control factor of the secondary negative carbon isotope series, in which the main factors can be secondary cracking, diffusion or ethane and propane Rayleigh fractionation In one or several ways to promote the formation of secondary negative carbon isotope series.