川西坳陷须四段砂岩碳酸盐胶结物形成机制——来自微量元素的证据  

Formation mechanism of carbonate cements in sandstone of the Xujiahe Member 4 in western Sichuan Depression:evidence from trace elements

作　　者：李文茂 张天操 钟玉梅 杨永剑 南红丽[1] LI Wenmao;ZHANG Tiancao;ZHONG Yumei;YANG Yongjian;NAN Hongli

机构地区：[1]中国石油化工股份有限公司西南分公司勘探开发研究院

出　　处：《海相油气地质》2022年第2期175-184,共10页Marine Origin Petroleum Geology

基　　金：国家科技重大专项课题“川西致密碎屑岩储层致密化与成藏关系研究”(编号:2016ZX05002-004)资助。

摘　　要：通过铸体薄片观察、阴极发光与电子探针实验分析等手段,对川西坳陷上三叠统须家河组四段长石岩屑砂岩、岩屑石英砂岩、岩屑砂岩的碳酸盐胶结物富集规律及元素含量变化进行了分析,发现不同类型砂岩均发育连晶方解石、晶粒结构方解石和白云石胶结物,但胶结物含量、阴极发光和微量元素组成等特征反映了胶结物离子来源具有差异性。连晶方解石阴极发光为亮黄色,Fe^(2+)、Mn^(2+)含量高,Sr^(2+)含量低,具有大气淡水成因的元素组成特点,证实了其受到大气淡水淋滤作用的影响。微晶、粉晶、细晶、中晶方解石具有橘红色到橘黄色的阴极发光特征,长石溶孔充填方解石的阴极发光具有暗明多个世代特征,反映其Fe/Mn值由高到低的变化规律。中晶方解石与充填孔隙的方解石具有高Fe^(2+)、Mn^(2+)含量和低Mg^(2+)含量的特征,认为这是由于长石及黏土矿物在埋藏成岩时期受到有机酸溶蚀的影响,成岩体系内高的Fe^(2+)、Mn^(2+)浓度,以及Fe^(2+)、Mn^(2+)在碳酸钙胶结物成岩过程中较高的分配系数决定了胶结物中元素的这种分布特征,因此晶粒碳酸盐胶结物离子应主要来源于埋藏期长石及黏土矿物的溶解。According to the characteristics of rock particle composition,the sandstone reservoir of the Xujiahe Member 4 of Upper Triassic in western Sichuan Depression can be divided into three categories:feldspar lithic sandstone,lithic quartz sandstone and lithic sandstone,of which the quality of feldspathic lithic sandstone reservoir is the best.By means of cast thin section observation,cathodoluminescence and electron microprobe analysis,it is considered that carbonate cement is an important factor affecting reservoir quality and continuous calcite and calcite cement with grain structure play a very important role in affecting reservoir quality.The enrichment law and trace element content change of carbonate cements are analyzed.It is found that different types of sandstone develop crystal stock calcite,crystalline calcite and dolomite cements,and the characteristics of cement content,cathodoluminescence and trace element composition reflect the differences of their sources.The cathodoluminescence of crystal stock calcite is bright yellow,with high Fe^(2+),Mn^(2+)contents,and low Sr^(2+) content.It has the characteristics of trace element composition caused by atmospheric fresh water,which confirms that it is affected by the leaching of atmospheric fresh water.Microcrystalline,very fine crystalline,fine crystalline and medium crystalline calcite has the cathodoluminescence of orange red to orange yellow,and the calcite filling in feldspar dissolved pore has the cathodoluminescence of dark and bright for multiple generations,reflecting the variation of Fe/Mn value from high to low.The middle crystalline calcite and calcite filling in feldspar dissolved pore are characterized by high Fe^(2+),Mn^(2+)contents and low Mg^(2+)content.It is considered that because feldspar and clay minerals are affected by organic acid dissolution during burial diagenesis,the resulting high Fe^(2+) and Mn^(2+) concentrations in diagenetic system,and the high distribution coefficient of Mn^(2+) and Fe^(2+) in the diagenetic process of carbonat

关 键 词：砂岩 碳酸盐胶结物 微量元素 须家河组 川西坳陷 

分 类 号：TE122.21[石油与天然气工程—油气勘探]