低熟烃源岩有机质在微生物作用下的地球化学特征

Geochemical Characteristics of Organic Matter in Low-mature Source Rocks with Microorganisms

对采自柴达木盆地涩北1井的2块钙质泥岩样品的饱和烃、芳烃和非烃馏分进行了系统的分析。检测出微生物特征生标MPI和角鲨烷化合物,在非烃馏分中检测出不饱和脂肪酸、异构脂肪酸和反异构脂肪酸。样品所处的地温为30℃左右,古环境细菌发育。同时检测出的8,14-断藿烷和烷基酮系列是微生物对沉积有机质改造的产物。在微生物作用下,低熟源岩有机质发生大分子向小分子转化,强烈的去甲基过程,藿烷C31/32αβ22S/(22S+22R)值和甾烷C29ββ/(ββ+αα)值等参数出现异常。微生物对低熟源岩的生物降解作用,有利于烃源岩生成气态烃,且对其降解具有饱和烃>芳烃>非烃的特征。

Based on two pieces of calcilutite from the Sebei Well 1 in Qaidam basin, a systematic analysis of saturation hydrocarbon and aromatic hydrocarbon and nonhydrocarbon is employed to study the complex hydrocarbon charging histories. By GC/MSD, we found the aqualane and MPI （2,6,10,15,19-pentanethyl-eicosane） of the microbial characteristic biomarkers and the unsaturated fatty acid and iso-fatty acid and trans-iso-fatty acid. In addition, the ground temperature of samples is about 30℃, which is good for microorganisms thriving. Hence there were some microorganisms in the palaeosedimentary environment of the samples. Microorganisms transformed sedimentary organic matters, so they produced the 8,14-secohopane and alkaneones by the degradation of bacterium-germs. With the participation of microbes, the lowmature source rocks would change greatly and the macro-molecules were partly transformed to the micromolecules and the demethylation was strong and the ratio of C31/32αβ22S/（22S＋22R）of hopanes and C29ββ/ （ββ-αα） of steranes occurred abnormally. The result shows that the microbial degradation was helpful to generating gaseous hydrocarbon. And the sequences of degradation of low-mature source rocks is saturation hydrocarbon〉aromatic hydrocarbon〉 nonhydrocarbon.