岩相对于湖相页岩孔隙结构特征及孔隙演化的控制机理

Effects of lithofacies on pore structure characteristics and evolution of lacustrine shales： A case study of the Jurassic Da’anzhai Member， central Sichuan Basin

康家豪 王兴志 曾德铭 黄梓桑 朱逸青 李博 谢圣阳 张芮

Jiahao KANG Xingzhi WANG Deming ZENG Zisang HUANG Yiqing ZHU Bo LI Shengyang XIE Rui ZHANG

湖相页岩各岩相的矿物网络格架通常具有差异性，对页岩原生孔隙与次生孔隙的形成和演化具有重要影响。以四川盆地中部侏罗系大安寨段页岩为研究对象，用取心井LA1井、RA1井和G10井页岩样品，进行全岩X射线衍射（XRD）分析、总有机碳含量（）测定、扫描电镜（SEM）观察和氮气吸附实验，研究了页岩岩石学特征与孔隙结构特征及其演化机制。研究结果表明：①大安寨段页岩划分为低碳介壳灰质粉砂质页岩岩相（OLLS）、中碳介壳灰质粉砂质页岩岩相（OMLS）、中碳介壳灰质黏土质页岩岩相（OMLC）、中碳粉砂质黏土质页岩岩相（OMSC）、高碳粉砂质黏土质页岩岩相（ORSC）、低碳黏土质页岩岩相（OLAS）以及中碳黏土质页岩岩相（OMAS）7种岩相。②页岩的储集空间主要以黏土矿物晶间孔为主，其中OLLS岩相脆性颗粒粒间孔较为发育，孔隙体积和比表面积相对较低。OMAS和OLAS岩相黏土矿物晶间孔最为发育，孔隙体积和比表面积最高。③碎屑矿物与黏土矿物的组成显著影响黏土矿物晶间孔孔径及有机质和黏土矿物的孔隙体积。碎屑矿物含量 < 25 %时，黏土矿物含量较高且孔隙体积较大，页岩总孔隙体积相应较大；碎屑矿物含量 ≥ 25 %时，有机质孔隙体积较大，但由于变化范围较大，页岩总孔隙体积受有机质和无机矿物共同影响。④矿物-孔隙网络结构演化表明，有机质与矿物组分控制了成岩事件的发生及其强度，导致现今各岩相孔隙结构和孔隙网络结构演化特征具有差异性。

Lacustrine shales typically exhibit distinct mineral-pore network frameworks for diverse lithofacies， significantly influencing the formation and evolution of primary and secondary pores in the shales. Based on data from whole-rock analysis by X-ray diffraction （XRD） mineralogy， total organic carbon （） content analysis， scanning electron microscopy （SEM）， and N adsorption experiments， we examine shale samples from the Jurassic Da’anzhai Member in cored wells LA1， RA1， and G10 in the central Sichuan Basin. To be specific， we investigate the petrological characteristics of these shale samples， as well as the characteristics and evolutionary mechanisms of their pore structures. The results indicate that the shales in the Da’anzhai Member can be categorized into seven lithofacies types： organic-lean limestone silty shale （OLLS）， organic-moderate limestone silty shale （OMLS）， organic-moderate limestone clay shale （OMLC）， organic-moderate silty clay shale （OMSC）， organic-rich silty clay shale （ORSC）， organic-lean argillaceous shale （OLAS） and organic-moderate argillaceous shale （OMAS）. Reserving spaces in these shales are dominated by intercrystalline pores in clay minerals. The OLLS exhibits well-developed intergranular pores among brittle grains， characterized by relatively low pore volume and specific surface area. In contrast， the OMAS and OLAS contain the most developed intercrystalline pores in clay minerals， featuring the highest pore volume and specific surface area. The clay-mineral intercrystalline pore diameters and the pore volumes of organic matter and clay minerals are significantly influenced by the compositions of detrital and clay minerals. Shales with a detrital mineral content of less than 25 % manifest a relatively high total pore volume due to the elevated pore volume of high-content clay minerals. For shales with a detrital mineral content of 25 % and above， the content varies greatly despite the high pore volume of organic matter. As a result， the total pore volume of these shales is jointly affected by organic matter and inorganic minerals. The evolution of the mineral-pore network frameworks indicates that organic matter and mineral components govern the occurrence and intensity of diagenetic events， leading to diverse evolutionary characteristics of the pore structures and pore network frameworks across various lithofacies at present.

10.11743/ogg20250211