北羌塘盆地东部上三叠统矿物成分特征分析及其地质意义

Analysis of mineral composition characteristics of the Upper Triassic in eastern part of the North Qiangtang Basin and its geological significance

本文以羌塘盆地雀莫错地区上三叠统地层为研究对象,利用红外光谱扫描获取岩心的矿物类型、含量、组合特征等信息,分析各主要矿物的空间变化规律,结合微观空间结构特征,研究该地层的沉积、储层及地质作用。结果表明:上三叠统矿物以碳酸盐和碎屑矿物为主,垂向上呈现规律性变化,其中碳酸盐矿物含量随深度增加逐渐增加,反之,石英、长石及黏土矿物等逐渐降低。黏土矿物以伊利石-蒙脱石为主,高岭石少见;绿泥石主要分布于上部巴贡组碎屑岩中;整体未见明显的白云石化现象。巴贡组以细颗粒沉积物为主,岩性致密,粒间孔、溶蚀孔少量发育,零星可见黏土矿物孔和微裂缝。波里拉组储集空间以微米级别孔隙为主,孔隙类型主要为晶间孔和黏土矿物孔。基于矿物和微观空间特征分析,研究区晚三叠世沉积环境由早期的深水沉积逐渐转换到浅水三角洲沉积,矿物成分从碳酸盐沉积转变为碎屑岩沉积,认为巴贡组地层早期为烃源岩主要发育期,黄铁矿等矿物存在指示还原环境,有利于烃类的生成和保存。

In this paper,the Upper Triassic in Quemocuo area,eastern Qiangtang Basin,is taken as the research object.The mineral type,content,combination characteristics and other information of the core were obtained by infrared spectrum scanning.The spatial variation of the main minerals was analyzed.The effects of sedimentation,reservoir and geological effects are studied.The results show that the mineral composition of the Upper Triassic is dominated by carbonate and clastic minerals.Vertically,it shows regular changes.Carbonate minerals gradually increase with depth,on the contrary,detrital minerals such as quartz,feldspar and clay miner⁃als gradually decrease from shallow to deep.Clay minerals are mainly illite-montmorillonite,kaolinite is rare;chlorite is mainly distributed in the clastic rocks of the upper Bagong Formation.Dolomization phenomenon mainly exists in Bolila Formation.Among them,a small amount of intergranular pores and dissolution pores are developed,and clay mineral pores and microcracks are sporadically visible.The Baobagong Formation is mainly composed of fine-grained sediments with dense lithology.Among them,a small amount of intergranular pores and dissolution pores are developed,and clay mineral pores and microcracks are sporadically visible.Based on the analysis of mineral composition and micro-spatial characteristics,the sedimentary environment of the Late Triassic in the study area gradually changed from the early deep-water deposition to the shallow-water delta deposition.The mineral composition changes from carbonate deposition to clastic rock deposition,and the color zone distribution is obvious.The analysis shows that the early stage of Bagong Formation is the main development period of hydrocarbon source rocks.The minerals(pyrite)indicating the reducing environment are generally developed,which is conducive to the generation and preservation of hydrocarbons.