页岩储层孔隙类型控制因素研究——以川东焦石坝地区龙马溪组为例

为了明确页岩不同岩相类型中孔隙类型的构成和垂向分布特征，选取川东龙马溪组7个页岩样品，进行氩离子抛光扫描电镜成像，对其孔隙类型进行定量分析。考虑到页岩的非均质性，每个样品选取5个区域，每个区域由100张放大倍数为14 000倍的SEM照片拼接组成（10 μm×10 μm），对每张SEM照片进行2000计点法统计各类型孔隙的面孔率，最后归纳得出每个样品中不同类型孔隙的平均百分含量。研究区可观察到3大类孔隙:粒间孔、粒内孔和有机质孔，不同岩相类型中各类型孔隙占比不同，龙马溪组自上而下页岩岩相类型变化趋势为黏土质页岩—粉砂质页岩—硅质页岩，随着黏土矿物含量逐渐减少，有机质含量和石英含量逐渐增加，其主要孔隙类型由粒内孔转变为有机质孔。脆性矿物含量对以粒缘孔为主的粒间孔数量起着控制作用；黏土矿物含量控制以片间孔为主的粒内孔发育程度；有机碳和自生石英含量决定着有机质孔的数量。龙马溪组下段的硅质页岩是页岩气最有利储层。 

Controlling factors of pore types in shale reservoirs:A case study from the Longmaxi Formation in Jiaoshiba area,eastern Sichuan Basin

Ar-ion beam scanning electron microscope (SEM) imaging and the quantitative analysis of pore types were performed on 7 shale samples from the Longmaxi Formation in the eastern Sichuan Basin to define the vertical distribution characteristics of pore types in various lithofacies of shale. Five regions were selected in each sample to accommodate the heterogeneity of the shales, and each region (100 μm×100 μm) was analyzed using 100 SEM photographs which were magnified 14 000×. A 2000 point-count method was employed to count the plane porosity of various pores on each SEM photograph, and then the average percentage of various pores in each sample was obtained. The results showed that interparticle (interP) pores, intraparticle (intraP) pores and organic matter (OM) pores could be observed in the study area, and the contents of various pore types were different in various lithofacies. The lithofacies of Longmaxi Formation changed from argillaceous shale, silty shale to siliceous shale from top to bottom. The main pore type changed from intraP pores to OM pores with the increase of TOC content and the decrease of clay content. The content of brittle minerals controlled the quantity of interP pores, clay content controlled the development degree of intraP pores, while TOC and authigenic quartz contents determined the quantity of OM pores. Siliceous shale in the lower segment of Longmaxi Formation is the most favorable reservoir for shale gas.