渝东南渝页1井下志留统龙马溪组页岩孔隙特征及其主控因素

Pore characteristics and controlling factors in the organic-rich shale of the Lower Silurian Longmaxi Formation revealed by samples from a well in southeastern Chongqing

富有机质黑色页岩的孔隙结构控制了页岩气的赋存状态和储气量。中国南方地区下志留统是页岩气发育的最重要层位之一。为研究页岩的孔隙特征及其主控因素,对以下志留统龙马溪组页岩气为勘探目标的渝页1井的岩心进行系统的采样,并进行了比表面和孔径、有机质成熟度(Ro)、显微组分、总有机碳(TOC)含量、全岩X射线衍射和粘土矿物含量等一系列分析测试。结果显示,黑色页岩的孔径主要分布于2～5nm,即以中孔隙为主;中孔体积占总体积的70%左右,微孔体积和宏孔体积分别占10%和20%左右。页岩孔隙结构(微孔体积、中孔体积和宏孔体积)和组成(碎屑矿物成分、粘土矿物成分、TOC和Ro)的相关关系分析表明:粘土矿物对微孔体积和中孔体积都具有控制作用,并且对中孔体积的控制作用更加显著;陆源碎屑含量的增加有利于宏孔体积的增加;有机质成熟度较高时和高成熟度有机碳含量都与宏孔隙体积呈正相关,这可能与高成熟有机质中nm级显微裂缝的发育导致宏孔体积增加有关。

Pores in organic rich black shales are important hosts of gas in the rocks. Pore structures control the occurrence and distribution of shale gas. The Lower Silurian shales in south China have great potentials for shale gas. We have carried out a series of important measurements including mineral surface area, pore vol- ume, pore diameters, total organic carbon （TOC）, vitrinite reflectivity （Ro） and components of organic mat- ter, and the abundance of detrital mineral grains and clay minerals to better understand the controls of pore volumes. The results show that the most important types of pores are mesopores with diameters varying between 2 nm and 5 nm; Mesopore volume accounts for 700/oo of the total volume, and micropore volume and macropore volume account for about 10~/00 and 200/oo, respectively. The relationships between the pore volumes and important measured parameters such as the abundance of detrital minerals, clay minerals, TOC and Ro indicate that the abundance of clay minerals has significant control on micropore and mesopore volumes, and a dominant control on mesopore volumes. The abundance of the detrital minerals has a positive effect on macro- pore volumes. The occurrence of nm scale microfractures in the organic matter with high maturity may be responsible for higher macropore volumes in the samples with Ro〉2.0% and higher organic matter maturity.