上扬子地区上震旦统—下志留统黑色页岩微孔隙特征

摘要

微孔隙(或微裂缝)作为页岩气的储集空间,对于页岩气的研究具有重要的作用.作者挑选了上震旦统一下志留统黑色页岩发育的上扬子地区10条剖面(上奥陶统一下志留统五峰一龙马溪组6条、下寒武统水井沱组2条、上震旦统陡山沱组2条),共20个样品进行场发射扫描电镜的精细扫描分析,初步识别出上震旦统—下志留统黑色页岩中的6种微孔隙(或裂缝)类型及其形成机制:格架孔主要是由碳酸盐岩和硅酸盐岩的颗粒和片状矿物堆砌、叠置而成；溶蚀孔主要与方解石、白云石和长石伴生,受到成岩晚期及埋藏过程中流体的溶蚀而成；生物体腔孔与生物的种类和数量紧密相关,主要由硅藻内部排列规则的孔集合而成；有机质孔的孔隙度与有机质类型和成熟度相关；白云石化孔主要是与方解石的白云石化作用密切相关,但极其少见.裂缝主要分为3种:(1)黏土矿物的脱水作用形成的微裂缝；(2)大片状的矿物与颗粒之间的微裂缝；(3)晶粒之间和颗粒内受到外力作用形成的微裂缝.%As the storage space of shale gas, micropores (including nanometer pores) are very important for the study of shale gas. Twenty classical Lower Paleozoic black shale samples are systematically scanned by the field emission scanning electron microscopy in this present paper. They are selected from 10 profiles in the upper Yangtze area, including 6 Upper Ordovician-Lower Silurian Longmaxi profiles, 2 Lower Cambrian Shuijingtuo profiles and 2 Upper Sinian Doushantuo profiles. Based on the study, six micropore types and their formation mechanism are identified as follows. The first micropore type is frame pore formed by the stacking of the particles and flaky minerals of carbonate rock and silicate rock. The second micropore type is dissolution pore formed by the dissolution of calcite, dolomite and feldspar during the late diagenesis and buried process. The third micropore type is organism cavity. It is related with the quantity and type of fossil. In this paper, the organism cavities are mainly in the diatom. The fourth micropore type is organopore, whose porosity is related with organic type and maturity. The fifth micropore type is dolomitization pore, which is extremely scarce and formed by the calcite dolomitization. The sixth micropore is microcrack. It can be divided into three kinds: (1) the tiny cracks formed by the dehydration of clay minerals, (2) tiny cracks between flaky minerals and particles, and (3) tiny cracks between grains and formed by external forces.