Hydrocarbon Generation Mechanism and Evolution Characteristics of Biomarkers on Low-Evolutionary Source Rocks of the Salt Lacustrine Facies

Investigation of the thermal simulation of low-evolutionary source rocks bitumen A of the salt lacustrine facies in Qaidam Basin indicated that the range of temperature on the hydrocarbon generating fastigium in the thermal function are 200～270℃,and the source rocks are characterized by high relative abundance of the nonhydrocarbon and asphaltene.The mature velocity of the biomarkers are different from the immature to low-mature to high-mature oil,and it's sequence is alkanehopanesterane.The polar compound in the nonhydrocarbon and asphaltene,which have some atom other than carbon,have some reactions after 300℃ in thermal simulation,for instance,dehydroxylation,decarboxylation,decarbonyl and the chain cleavage.The ratio of sterane C29ββ/(ββ+αα) is very high in low-evolutionary stage,indicating that there are some bacterium-germs in this area.In low temperature range of low-evolutionary source rocks in Qaidam Basin have generated a significant volume of hydrocarbon,consequently the activation energy of source rocks would become down because the depositional organic matter have been rebuilt by the bacterium-germs.