四川盆地南缘骑龙村剖面五峰-龙马溪组黑色页岩孔隙大小特征的重新厘定

Redefinition of pore size characteristics in Wufeng Formation-Longmaxi Formation black shale of Qilongcun section in southern Sichuan Basin,China

以四川盆地南缘习水骑龙村剖面的上奥陶统—下志留统五峰-龙马溪组页岩气储层为例,探讨黑色页岩的孔隙大小特征与气体赋存的相关性。运用氮气吸附法对储层的微观孔隙进行定量测定,通过扫描电镜对页岩孔隙的微观特征进行定性分析,再结合页岩有机碳含量、Si/Al比值,对页岩的孔隙结构特征进行表征:(1)在排除SiO2质量分数>70%的页岩样品(孔隙主要以>1μm的宏孔为主)基础上,SiO2质量分数≤70%的页岩样品的孔隙中3～10nm的微孔,占孔隙总体积的50%～83%(平均值为71%),占比表面积的范围为86%～97%(平均值为94%);(2)甲烷吸附量、Si/Al和有机碳含量分别与3～10nm微孔的孔隙体积、比表面积成明显的正相关。综合表明四川盆地南缘五峰-龙马溪组页岩中孔隙<10nm的微孔才是主要气体存储空间。

Based on a study of the shale gas reservoir of the Wufeng Formation-Longmaxi Formation of Upper Ordovician-Lower Silurian in the Qilongcun section, Xishui County on the south margin of Sichuan Basin, this paper analyzes the relationship between the pore size of the black shale and the occurrence of gas. The micropore characteristics are described by several methods, including quantitative analysis using nitrogen adsorption method, the qualitative analysis being scanned by scanning electron microscopy, and the ratio analysis of total organic carbon （TOC） and Si/A1. The characteristics of the pore structure of the shale are as follow. （1） The sizes of the main micropores of the samples with SiO2≤70% are in a range of 3--10 nm, taking up 50%-83% （The average is 71%） of the total volume of pores and 86--97% （The average is 94%.） of the specific surface area. （2） The obvious positive correlation between the methane adsorption capacities, the ratio of Si/ A1, TOC and the pore volume and specific surface area of the micropores （The pore diameter is 〈10 nm. ） is shown. These results imply that the micropores （The pore diameter is 〈10 nm. ） are the main spaces of reservoiring gas in the Wufeng Formation-Longmaxi Formation of Upper Ordovician- Lower Silurian on the south margin of Sichuan Basin.