CARBON ISOTOPIC FRACTIONATION EFFECT CAUSED BY MATURITY DURING THE GENERATION OF COAL-PYROLYSIS HYROCARBONS

The carbon isotopic fractionation effect of 3 types of coal under different pyrolysis temperatures has been studied through the hydrocarbon generation-expulsion pyrolysis simulation experiment in a semiClosed system.The results indicate that the carbon isotopic fractionation effect caused by the maturity differences changes with the different organic types of the coal.The fractionation effect of the pyrolysis hydrocarbons from the humous coal is significant,whereas the carbon isotope of the coal itself changes little with maturity.The possibility of the secondary cracking of the pyrolysis hydrocarbons increases greatly under a higher maturity level,resulting in the significant increase of the carbon isotopic compositions of the individual n-alkanes,especially the residual hydrocarbons.The isotopic distribution curves of the individual n-alkanes from the same source rock under different temperatures are very similar,indicating that,alike the value,the curve shape of the isotope may also provide a very important basis for oil-source correlation.