渝东南地区龙马溪组高演化页岩微纳米孔隙非均质性及主控因素
Micro/Nano Pore Heterogeneity and Main Controlling Factors of the High-Maturity Longmaxi Formation Shale in Southeastern Chongqing

摘要： 对页岩气赋存的主要场所页岩孔隙的研究是解决页岩气赋存和保存机理的关键，但目前缺少有效的手段去定量刻画高演化页岩微纳米孔隙的非均质性特征。通过低压N2吸附/解吸、高压压汞、场发射扫描电镜(FE-SEM)等实验，运用分形维数对渝东南地区龙马溪组高演化页岩微纳米孔隙非均质性进行了定量分析。结果表明：高演化页岩的微纳米级孔隙非均质性极强。中孔(2.0~50.0 nm)中2.0~4.5 nm 的孔隙分形维数平均2.853 4，4.5~50.0 nm 的孔隙分形维数平均2.7367，这种极强非均质性主要受有机质控制。总有机碳(TOC)含量大于1.7 %时，有机质孔在中孔中占主导地位，粘土矿物含量的增加会在一定程度上增加中孔的非均质性。宏孔(＞50.0 nm)分形维数平均2.8441，非均质性较强，主要受石英和碳酸盐等脆性矿物控制，随着碳酸盐矿物含量的增大，非均质程度增加，有机质对页岩宏孔的非均质性影响不明显。
Abstract: Studying shale pores is the key to understand the mechanism of shale gas occurrence and accumulation. But there is little effective means to quantitatively depict micro/nano pore heterogeneity characteristics of high-maturity shales. This article quantitatively analyzed micro/nano pore heterogeneity and main controlling factors of the high-maturity Longmaxi Formation Shale in southeastern Chongqing through the low pressure N2 adsorption/desorption, high-pressure mercury injection (MIP), and field emission scanning electron microscopy (FE-SEM) experiment together with the use of the fractal dimension. The results show that micro/nano pores develop very well in high-maturity shale. Mesopores are mainly slit-shaped clay interparticle pores and ink-bottle-shaped organic pores. Fractal dimensions of pores between 2.0 nm and 4.5 nm in diameter have an average value of 2.853,4, while fractal dimensions of pores between 4.5 nm and 50.0 nm in diameter have an average value of 2.736,7. The strong heterogeneity is mainly controlled by organic matters. When total organic carbon (TOC) content is less than 0.9%, the pores provided by minerals play dominant role, while the TOC content is larger than 1.7%, organic pores play dominant role. In addition, the increase of clay mineral content will increase the mesopores heterogeneity in a certain extent. Macropores are mainly composed of slit-shaped interparticle pores and a small amount of ink-bottle-shaped organic pores. Fractal dimensions of macropores have an average value of 2.844,1, which show strong heterogeneity, indicating the pore structure is complex. The heterogeneity of macropores is mainly controlled by quartz and carbonate minerals. With the increase of carbonate minerals content, the degree of heterogeneity increases. As organic pores size is relatively small, they have no obvious influence on shale macropore heterogeneity