柴达木盆地第四系脂肪酸分布特征与生气潜力的关系

Relationship between distribution of fatty acids and gas-generating potential in Quaternary in Qaidam basin

康晏 王万春 张道伟 任军虎

Kang Yan Wang Wanchun Zhang Daowei Ren Junhu

通过研究柴达木盆地涩北地区第四系540～1 490 m纵向剖面上泥岩可溶有机质中的脂肪酸(甲酯)类化合物,发现在层段1 200～1 381 m内正构脂肪酸的偶奇优势指数有非常剧烈的变化,这是由有机质输入和细菌作用为主导的多种因素造成的;在层段796～810.8,1 188.24～1 210,1 291.54～1 300.74 m内脂肪酸的几种生标指数如脂肪酸含量、偶奇优势指数以及组成分散性指数的值都为谷值,这是由于在这几个层段内有机质输入类型以水生生物型为主,因而易被细菌降解,说明以内源有机质输入类型为主的源岩生气潜力较高;在1 188.24～1 210 m层段内发现了丰富的不饱和酸和异构酸,说明在这个层段内地化环境以及气源岩类型较适宜细菌的生存发育。这种特殊的脂肪酸分布可能指示了优质气源岩类型。

Fatty acids(methyl ester)of dissoluble organic matter in Quaternary mudstone samples obtained from 540-1 490 m interval in Sebei area of Qaidam basin are analyzed through GC-MS.Even-odd predominance index of normal fatty acids varies greatly in 1 200-1 381 m interval.It is caused by various factors,of which the input of organic materials and bacterial action are dominant.In intervals of 796-810.8 m,1 188.24-1 210 m and 1 291.54-1 300.74 m,several biomarker indexes of fatty acids,such as content of fatty acids,even-odd predominance index and component dispersancy index,are at their valleys,as the major organic matters input in these intervals are of aquatic organism type,which are easy to be degraded by bacteria.All these indicate that source rocks dominated by indigenously sourced organic matter type have relatively high gas generating potential.Abundance of unsaturated acid and isomeric acid are discovered in 1 188.24-1 210 m interval,indicating that the geochemical environment and type of gas source rock in this interval are suitable for living and growth of bacteria.This specific fatty acid distribution might indicate high quality gas source rocks.

10.11743/ogg20050614