Thermal Pyrolysis of Hydrocarbon Generation for Marine Hydrocarbon Sources in Marine Sequence of South China and Stable Carbon Isotopes of Gas Products

The hydrous pyrolysis experiments for potential hydrocarbon sources in the marine sequence of south China were subjected in the high pressure and geological condition simulation vessels.The results indicate that the productivity of hydrocarbon gas generation for hydrocarbon sources is various,the highest productivity for crude oil(light oil and condensate),the secondary productivity for the dispersed soluble organic matter(solid bitumen and heavy oil),and the poor productivity for kerogen.The yield of hydrocarbon gas products for hydrocarbon sources is positively related with total organic carbon,soluble organic matter and organic matter type,but negatively with thermal maturity.The carbon isotopes of hydrocarbon sources inhibit the tendency of methane carbon isotopes.The carbon isotopic composition of methane derived from the hydrocarbon source with the lighter carbon isotope is lighter than that of methane from the hydrocarbon sources having the heavier carbon isotope.With thermal maturity increase,δ13C value of methane increases but is less than that of its hydrocarbon sources.The δ13C values of ethane and propane in the pyrolysate products also increase with pyrolysis temperature increase,gradually approaching of the carbon isotope of their sources at the peak stage of hydrocarbon generation.At high-over mature stages,the δ13C values of ethane and propane are often more than that of their sources.Thus the carbon isotope of heavy hydrocarbon gases would be ineffective as gas genetic indicators.The contents and isotope compositions of carbon dioxide are different between kerogens and dispersed soluble organic matter.The carbon isotope fractionation between carbon dioxide and methane derived from soluble organic matter is greater than that from kerogen.During the process of hydrocarbon generating for hydrocarbon sources,the carbon isotope compositions of kerogen and liquid hydrocarbons are mainly controlled by precursor type,tracing their sources.Therefore,the carbon isotope compositions of kerogen and liquid hydrocarbons can be used to perform oil-source correlation and tracing hydrocarbon sources.