川西北地区泥盆系烃源岩地球化学特征分析

Geochemical characteristics analysis of Devonian source rocks in northwestern Sichuan basin

基于区域地质、烃源岩发育环境,并综合应用烃源岩有机地球化学、有机岩石学、微量元素等实验技术,探讨了川西北地区泥盆系烃源岩地球化学特征。分析结果表明:川西北地区发育泥盆系观雾山组(D2g)生屑灰岩、养马坝组(D2y)泥灰岩两套烃源岩,推测甘溪组为烃源岩可能发育层系;泥盆系烃源岩TOC平均值已达3.08%,且大于1.0%的样品占总数的76%,有机质丰度较高,总体上是一套有机质丰度高的海相烃源岩;桂溪地区和朝天地区泥盆系烃源岩干酪根类型分别为Ⅰ—Ⅱ1型和Ⅱ1型,有机质类型以腐泥型为主;野外露头剖面的泥盆系烃源岩处于成熟—高成熟阶段,因而埋深的泥盆系烃源岩则处于过成熟生气阶段;泥盆系烃源岩样品正构烷烃特征表明母质来源以低等水生生物为主,古盐度范围、低Pr/Ph值、硫芴占绝对优势等特征反映了还原性沉积环境。川西北地区泥盆系烃源岩地球化学特征分析结果表明了该地区油气来源的多样性,对该区下步油气勘探部署具有参考价值。

Considering the development setting of regional geology and source rocks and with comprehensive application of experimental techniques on source rock organic geochemistry,organic petrology,and microelement,etc.,the geochemical characteristics of Devonian source rocks in northwestern Sichuan have been analyzed.The analysis indicates that in northwestern Sichuan,two sets of source rocks have been developed,referring to the Devonian bioclastic limestone of the Guanwushan Formation（D2 g）and the marlstone of the Yangmaba Formation（D2 y）,and besides,the Ganxi Formation is possibly with developed source rocks as well;Devonian source rocks with the TOC averaging3.08%and greater than1.0%for 76%samples are rel-atively high in organic abundance,wholly regarded as a set of marine source rocks with high organic abundance;in the Guixi and Chaotian areas,the kerogen of Devonian source rocks are type I—II1 and II1,and organic matters are mainly sapropel;in view of the Devonian source rocks in outcrops being in the stage of maturity to high maturity,the Devonian source rocks buried deeply is indicated to be in the stage of over-maturity and gas generation;the features of n-alkanes for Devonian source rock samples suggest the source mainly comes from lower aquatic organisms and the features of ancient salinity range,low Pr/Ph value,absolute advantage of dibenzothiophene and others reflect the depositional setting of reducibility.The analysis of geochemical features for Devonian source rocks in northwestern Sichuan reveals diverse oil and gas sources,providing reference for the further oil and gas exploration deployment in the region.