【作者】 李吉君；

【导师】 卢双舫；

【作者基本信息】 大庆石油学院 ， 矿产普查与勘探， 2005， 硕士

【摘要】 天然气是一种以轻烃为主的混合物,由于缺少大分子指纹化石,许多重要的成因信息难以单纯依靠组分获得。同位素效应的存在弥补了这一缺憾,同位素分馏是同位素效应的集中体现。影响天然气碳同位素值的主要因素为母质类型和成熟度。受“结构效应”的影响,相同成熟度条件下,由腐殖型有机质生成的煤型气碳同位素值比由腐泥型有机质生成的油型气的重。而对于某种确定成因的天然气,随成熟度的增加其δ13C 值一般是增大的。生气母质中不同成气官能团具有不同的碳同位素组成和12C-12C 与13C-12C 的活化能差。在描述天然气碳同位素分馏的众多模型中,从早期的静态模型到后来的以Rayleigh 方程为基础的分馏模型,再到现在的动力学模型是一个不断完善过程:静态模型无法动态地再现天然气的演化历程,无法预测天然气形成过程中的各种复杂变化;以Rayleigh 方程为基础的分馏模型把碳同位素的分馏体现在一个恒定的分馏因子上;动力学模型均认识到同位素动力学效应是温度和时间的函数。但是,Cramer1、Cramer2模型却都有缺陷,均认为所有平行反应对应的母质即不同成气官能团具有相同的碳同位素组成,这一假设看来并不合理,而且Cramer1 模型更大胆地假设不同成气官能团的12C-12C 与13C-12C 的键能差相同,这与量子化学理论相背。Cramer3 模型基本摆脱了这些不足,它从实际生成含12C及13C的甲烷量出发,来计算碳同位素动力学效应。建模基础的不同造成了拟合效果的不同:以Rayleigh 方程为基础的模型和Cramer1 模型仅仅能够近似地模拟出碳同位素值随着热解温度的升高而变重的部分,而对低温段和高温段存在的异常变化都模拟不出来;Cramer2 模型能对碳同位素的整体演化趋势进行较好的拟合,但存在波动;Cramer3 模型能完全模拟出碳同位素值的演化趋势,是最为完善的模型。应用静态模型,直接应用天然气的碳同位素值可以确定天然气成因类型及成熟度。而应用同位素动力学模型结合盆地的热史和埋藏史则可以对气藏的成藏史加以研究。更多还原

【Abstract】 Nature gas is a kind of mixture in which light hydrocarbons are dominant, it is very difficult to acquire some important origin information because macromolecule fingerprint fossil is absent. Presence of isotope effect fetches up this regret. Important factors affecting carbon isotope value of nature gas are parent material type and maturity. Under the effect of “structure effect”, carbon isotope value of coaliferous gas generated from humus is greater than that of petroliferous gas generated from sapropelic substance if they have same maturity. Popularly, carbon isotope value of nature gas from certain parent material becomes greater and greater as its maturity increases. Different functional groups in generating gas parent material have distinct isotope composition and ?Ea between 12C-12C and 13C-12C. The models describing nature gas carbon isotope distillation become more and more perfect from early static models to models based on Rayleigh expression and kinetic models. Static models can not dynamically describe nature gas evolvement course and can not forecast all kinds of complicated variety in the process of natural gas generation; and models based on Rayleigh expression incarnate carbon isotope distillation using a constant distillation gene; but kinetic models realize isotope kinetic domino offect is a function of temperature and time. But models of Cramer1 and Cramer2 have bugs: they consider different generating gas functional groups corresponding with parallel reactions have same carbon isotope constitute, this is not reasonable. In Cramer1 model it is boldly supposed that ?Ea between 12C-12C and 13C-12C of different functional groups is equal which breaches quantum chemistry theory. Cramer3 model casts off these flaws, it calculates isotope kinetic effect using actual genertated quantity of 12C1 and 13C1. Models’fitting effect is different as they are founded on distinct bases: models based on Rayleigh expression and Cramer1 model can only simulate the part in which carbon isotope value become great when temperature increases, for abnormal varieties in parties of low temperature and high temperature they fail. Cramer2 model can simulate carbon isotope value curve preferably, but fluctuate is unavoidable. Only Cramer3 model can simulate it completely, so it is the most perfect. Genesis type and maturity of nature gas can be confirmed using carbon isotope value by static models. Using kinetic models and combining basin’s thermal history and embedding history we can study gas reservoir form history.更多还原