江陵凹陷古近系新沟嘴组下段原油芳烃馏分地球化学特征及油源对比

Geochemical Characteristics of Aromatic and Oil-source Correlation in Crude Oils from the Lower Member of the Paleogene Xingouzui Formation in Jiangling Depression

【目的】油气来源对比是油气勘探的基础,为扩大江陵凹陷油气资源勘探领域。【方法】基于前期饱和烃分析结果,利用色谱—质谱分析技术对江陵凹陷古近系新沟嘴组下段原油的芳烃馏分进行了分析研究,对原油来源进行了探讨。【结果】研究区原油可分为两大类:Ⅰ类原油取自万城断裂构造带和公安单斜带,其母源形成于一般还原环境并且水体具有一定盐度的半深湖相沉积环境,萘系列及三芳甾烷系列高碳数异构体比值体现其母质类型较好以及陆生高等植物输入较少的特点,该类原油整体处于成熟—高熟阶段,其中万城断裂构造带中的万13井和万12井和公安单斜带中的耀5井是高成熟原油,推测处于各自构造单元中最接近油藏充注点的位置;Ⅱ类原油取自荆州背斜带,成熟度低于Ⅰ类原油,母质类型以低等水生生物输入为主但相较于Ⅰ类原油接受了更多的陆生高等植物输入,形成于高盐度、强还原的深湖相沉积环境,且位于荆州背斜带中部及东南部的Ⅱ2类原油相较于荆州背斜带西北部的Ⅱ1类原油成熟度更低、陆生高等植物输入更多。【结论】万城断裂构造带的Ⅱ油组和Ⅲ油组为Ⅰ类原油的主要烃源岩,同时存在来自荆州背斜带Ⅰ油组的贡献,高的成熟度特征可能指示该类原油还存在除本文外的其他区域或层位的贡献;Ⅱ类原油主要来自荆州背斜带和万城断裂构造带的Ⅱ油组,同时存在荆州背斜带北部Ⅲ油组的贡献。

[Objective]Comparison of oil and gas sources is the foundation of oil and gas exploration,in order to ex-pand the field of oil and gas resources exploration in Jiangling Depression.[Methods]On the basis of the previous saturated hydrocarbon analysis results,the aromatic fraction of the crude oil from the lower member of Paleogene Xin-gouzui Formation in Jiangling Depression was analyzed by gas chromatography-mass spectroscopy(GC-MS),and the source of crude oil was discussed.[Results]The crude oil in the study area could be divided into two main types:TypeⅠ,located in the Wancheng fault structural belt and Gongan monocline belt,was formed in a semi-deep lacus-trine sedimentary environment with a certain salinity in a reducing environment.Naphthalene series compound and the ratio of the high molecular weight isomers of the triaromatic sterane series reflected the characteristics of better parent material types and less input from terrigenous higher plants.It was in mature-high maturity stage.Wan13 and Wan12 in the Wancheng fault belt and Yao5 in the Gongan monocline belt belonged to highly mature crude oil,which were presumed to be in the position closest to the reservoir charging point in their respective tectonic units.TypeⅡ,located in the Jingzhou anticline belt,had a lower maturity than TypeⅠ.Its parent materials were im-ported from lower aquatic organisms but received more input from higher terrestrial plants than typeⅠ.It was formed in a deep lacustrine sedimentary environment with high salinity and strong reduction.Compared with typeⅡ1,typeⅡ2 had lower maturity and more terrestrial higher plant inputs.[Conclusions]TypeⅠwas primarily derived from the X-Ⅱand X-Ⅲof Wancheng area,and the source rocks from X-Ⅰof the Jingzhou anticline belt also had certain contributions.The high maturity characteristics may indicate the contribution of other regions or formations.TypeⅡwas primarily derived from X-Ⅱof the Wancheng area and Jingzhou anticline belt,and it also had some contribution from X-Ⅲof the northern Jingzhou anticline belt.