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

Key words: 
• lowevolutionary source rocks

Abstract: 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 alkane>hopane>sterane. 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 C29ββ/(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.