海相页岩纹层特征、成因机理及其页岩气意义

Characteristics,genetic mechanism of marine shale laminae and its significance of shale gas accumulation

基于前期研究及文献调研,结合薄片分析、扫描电镜、地球化学相关测试等方法,分析海相页岩纹层及纹层组的类型和发育特征,讨论其多源成因机制、储层非均质性的影响以及其与页岩气富集的关系。研究结果表明:基于纹层形态学和矿物学特征,以川南地区五峰组—龙马溪组海相页岩为例,纹层多发育4种产状(板状、条带状、波状和透镜状)、6种类型(硅质纹层、黏土纹层、富有机质纹层、碳酸盐岩纹层、黄铁矿纹层和斑脱岩纹层)、3种纹层组(硅质−黏土纹层组、硅质−富有机质纹层组和硅质−黏土纹层组);海相页岩纹层成因复杂,通常是在不同水深范围内受不同水动力条件作用而成,或在沉积过程中具有悬浮沉降、沉积物输入变化、生物生产力波动以及后期成岩作用等多种地质因素的叠加效应;纹层的多样性影响页岩的储集空间类型、孔隙结构和微裂缝展布,导致海相页岩储层具有强非均质性;五峰组—龙马溪组海相页岩中高有机碳质量分数、高孔隙度、高含气性层段往往发育富有机质纹层、生物硅质纹层以及二者的纹层组合,不同笔石带纹层和纹层组类型均具有特殊性,大量有机质呈纹层状分布,LM1—LM7生物笔石带页岩纹层及纹层组合类型从单一向多元化发展,为页岩气提供了更多的储集空间。

Based on the previous research and reference,the types and development characteristics of marine shale laminae and laminae association were analyzed.The multi-source genetic mechanism,the influence on reservoir heterogeneity and its relationship with shale gas enrichment were discussed by thin section analysis,scanning electron microscope and geochemical correlation test.The results show that based on morphological and mineralogical classification,taking the marine shale of Wufeng—Longmaxi Formation in southern Sichuan as an example,there are 4 types of occurrences(plane,banded,microwave and lenticular),six types of laminae(siliceous laminae,clay laminae,organic laminae,carbonate laminae,pyrite laminae and bentonite laminae),and three types of laminae association(siliceous-clay laminae,siliceous-organic laminae,clay-organic laminae).Marine shale laminated genesis is complex,which is often formed under different hydrodynamic conditions from different water depths,or the superposition effect of multiple geological factors such as suspension,changes in sediment input,fluctuations in biological productivity and late diagenesis in the sedimentary process.The diversity of laminae directly controls the reservoir space types,pore structure and microfracture distribution of shale,resulting in heterogeneity of shale reservoir.Organic-rich laminae,biological siliceous laminae and its association are often developed in the Wufeng—Longmaxi formation shale with high w(TOC),high porosity and high gas content.Different graptolite laminae and laminae association have particularity.A large amount of organic matter is distributed in laminae,the laminae and laminae association of LM1—LM7 bio-graptolite are developed from single to diversified,and the development of laminae provides more storage space for shale gas.