页岩微观孔隙特征及源-储关系r——以川东南地区五峰组-龙马溪组为例

摘要

页岩既是页岩气的烃源岩,又是页岩气的储层. 运用氩离子抛光扫描电镜技术对川东南地区五峰组-龙马溪组页岩的有机质、无机矿物、孔隙等微观特征进行描述,将有机质、孔隙作为一个"源-储"系统来分析其空间分布状态与时间演化关系. 研究表明,有机质孔比无机质孔对赋存页岩气更重要;迁移有机质比原地有机质更发育有机质孔. 无机矿物孔隙赋存大量的迁移有机质,在页岩气形成过程中发挥重要作用. 五峰组-龙马溪组中含有较多的硅质等刚性颗粒矿物,可以形成坚固的粒间孔隙体系,在成油期孔隙度高、孔隙大且连通性好,可以保存大量的迁移有机质. 刚性颗粒粒间孔隙中赋存迁移有机质,迁移有机质在其中演化成为固态有机质,其中的有机质孔中赋存天然气,构成最佳的源-储匹配关系,最有利于形成和富集页岩气. 页岩中的粘土矿物晶间孔在早期的成岩阶段大多已丧失,少量的在胶结物晶粒支撑与内部流体压力双重保护之下仍赋存有机质和有机质孔. 黄铁矿集合体形成粒间和内部晶间孔隙,部分孔隙可以赋存有机质和较小的有机质孔,但总量有限.%Shale serves as both hydrocarbon source rock and reservoir of shale gas .The microscopic features of the Wufeng and Longmaxi Fms shale in Southeast Sichuan Basin such as organic matters , inorganic minerals and pores are described with the technology of Argon ion milling and scanning electron microscop .The organic matters and the pores are regarded as a source-reservoir system to analyze the relationship between their spatial distribution and temporal evolu-tion.The research shows that organic pores are more important than inorganic mineral pores in respect of hosting shale gas,and migrated organic matters develop more pores than in-situ organic matters.Inorganic mineral pores play an impor-tant role in the formation of shale gas by hosting abundant migrated organic matters .With plentiful rigid mineral grains such as quartz ,the Wufeng and Longmaxi Fms shales had a hard intergranular pore system of inorganic minerals with high porosity,big pores and good connectivity in hydrocarbon generation stage ,which can preserve abundant migrated liquid organic matter(oil).The migrated organic matters were stored in intergranular pores among rigid grains and then evolved into solid organic matter with organic pores by exsolution of gaseous hydrocarbons ,and the gas filled the organic pores . This is the most favorable source-reservoir matching relation for the generation and enrichment of shale gas .Most of the intraplatelet pores in clay mineral aggregates had been lost in the early diagenetic stage ,while a small amount of organic matters with organic pores were preserved under the support of cements and fluid pressure between the platelets .Pyrite aggregates form intergranular and intercrystal pores , part of which can preserve organic matter and organic pores withsmaller size ,but their total amount is limited .