低熟泥灰岩、钙质泥岩干酪根脂肪酸的分布特征及赋存形式

Distribution and occurrence of kerogen fatty acids in low mature marl and calcareous mudstone

孟仟祥 郑建京 房玄 孙敏卓

Meng Qianxiang Zheng Jianjing Fang Xuan Sun Minzhuo

柴达木盆地第三系低熟、低有机碳烃源岩干酪根中检测出直链一元酸、直链二元酸和芳香酸3个系列。其中以直链一元酸相对丰度最高,C十六酸为主峰(饱和脂肪酸),呈明显偶碳数优势特征。干酪根脂肪酸赋存量是强干酪根脂肪酸的3倍以上,且前者直链二元酸的相对丰度大大高于后者。以脂肪酸钙(镁)盐和脂肪酸形式富集在源岩碳酸盐晶体中的脂肪酸含量远远大于赋存在干酪根网络中的量。当碳酸盐晶体被高温(及复杂地质条件)分解时,这些脂肪酸盐和脂肪酸主要会被裂解为小分子烃———气态烃。柴达木盆地沉积有机质中的硫以五元、六元和八元环状稳定态存在,因其强烈的电负性,可能会对脂肪酸(盐)的富集及稳定存在作出贡献。

Three acid series,including straight chain monoacid,straight chain binary acid and aromatic acid,have been detected in the kerogen of low mature Tertiary source rocks with low organic carbon content in Qaidam basin.Relative abundance of straight chain monoacid is the highest among these three acid series,and C acid occurs as the main peak(saturated fatty acid),with obvious even carbon number predominance.The volume of kerogen fatty acid is over three times that of enhanced kerogen fatty acid,and the former has much larger relative abundance of straight chain binary acid than the latter.In addition,the volume of fatty acid that enrich in carbonate crystals of source rocks in the form of calcium(magnesium)fatty acid salt and fatty acid is far greater than that occur in kerogen network.When these carbonate crystals were decomposed at high temperature(and at complex geologic conditions),the fatty acid salt and fatty acid might be cracked into small molecular hydrocarbon,i.e.,gaseous hydrocarbon.The sulfur in deposited organic matters in the study area occur as pentabasic,hexabasic and octatomic ring stable states,and would make contribution to the enrichment and existence of fatty acid(salt)due to its strong electron negativity.

10.11743/ogg20050607