Carbon Isotope Fractional Distillation Of Natural Gas And Its Application In Xujiaweizi Area

Petroleum has complex compositions in which abundant great molecules can be regarded asfingerprint fossil to indicate source rock character and its maturity. Natural gas is different frompetroleum, it is a kind of mixture in which light hydrocarbons are dominant, so it is very difficultto acquire a lot of important information about cause of formation through its compositions only,such as travel path, generation and congregating history. As a result, it becomes very importantto identify character of natural gas through stable isotope.Different functional groups in generating gas parent material have distinct isotopecomposition and ?Ea between ¹²C-¹²C and ¹³C-¹²C. The models which describe nature gascarbon isotope distillation become more and more perfect from early static models to modelsbased on Rayleigh expression and kinetic models. Static models can not dynamically describenature gas evolvement course and can not forecast all kinds of complicated variety in the processof natural gas generation;and models based on Rayleigh expression incarnate carbon isotopedistillation using a constant distillation gene;but kinetic models realize isotope kinetic dominooffect is a function of temperature and time. Isotope kinetic models are based on experiment tosimulate isotope value evolvement rule of natural gas in generation process. They can resolvesome problems which can not be realized through static models. For example, they can connectisotope value evolvement rule with thermal history and bury history of basin to study gasreservoir formation history.But models of Cramer1 and Cramer2 have bugs: they consider different generating gasfunctional groups corresponding with parallel reactions have same carbon isotope constitute, thisis not reasonable. In Cramer1 model, it is boldly supposed that ?Ea between ¹²C-¹²C and ¹³C-¹²Cof different functional groups is equal which breaches quantum chemistry theory. Cramer3model casts off these flaws, it calculates isotope kinetic effect using actual generation quantity of¹²CH4 and ¹³CH4. Cramer3 model can simulate isotope value evolvement curve completely, it isthe most perfect.In this paper, we combine the burial history and thermal history of Xujiaweizi area, usingthe cramer3 fractionation model to study gas accumulative pattern and gas reservoir formationperiod, such follow conclusions can be obtained: The gas reservoir formation period ofYingcheng formation gas reservoir of Xushen1 well ranges form 100 to 73Ma, and it is anaccumulative gas reservoir.Key words: natural gas, stable carbon isotope, fractionation model, kinetics model, Xujiaweizi...