盐湖相低演化烃源岩的生烃机理及生物标志物演化特征——沥青“A”热模拟

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

柴达木盆地盐湖相低演化烃源岩沥青"A"的热模拟研究表明:在热作用下其排烃高峰在热模拟温度较低区间220～270℃,且以非烃和沥青质相对丰度最高为特征。沥青"A"在由未熟—低熟—成熟的演化过程中,各系列生物标志物的成熟速率不同,表现为正构烷烃>藿烷>甾烷。非烃和沥青质中含杂原子的极性化合物在热模拟温度300℃后开始大量发生脱羟基、脱羧基、脱羰基及链断裂反应。沉积有机质在低演化阶段甾烷C29-ββ/(ββ+αα)值异常高表明该地区细菌微生物发育。柴达木盆地低演化烃源岩在较低温度区间大量排烃,是细菌微生物对沉积有机质改造后其活化能大大降低所致。

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 asphahene. 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 C29 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.