川北元坝地区大安寨段页岩微观孔隙空间定量表征

为了分析元坝地区大安寨段湖相页岩的天然气赋存特点,通过扫描电镜、氮气吸附、高压压汞等实验方法,研究了该区大安寨段页岩的孔隙类型与孔径分布,并探讨了页岩的孔隙结构对页岩气赋存状态的影响。结果表明:页岩中发育无机质孔隙(76.92%)、有机质孔隙(9.17%)与微裂缝(13.91%),其中无机质孔隙主要为蒙脱石伊利石化过程中形成的黏土矿物孔隙,有机质孔隙欠发育的原因与有机质类型以Ⅲ型为主且总有机碳含量低有关;页岩的全孔径分布中,微孔、中孔与宏孔分别贡献6.76%、76.92%与16.30%的孔体积。可见,元坝地区大安寨段页岩以无机孔为主,主要发育中-宏孔,与储层高温高压共同控制了该区页岩气的赋存方式以游离气为主。

Quantitative characterization of microscopic pore structure of shale in Da'anzhai member in Yuanba area, Northern Sichuan Basin

In order to analyze the characteristics of natural gas occurrence of the lacustrine shale in Da''anzhai member in Yuanba area. Using scanning electron microscope (SEM), nitrogen adsorption, high-pressure mercury injection and other analytical techniques, the pore types and pore size distribution of lacustrine shale in Da''anzhai member of Yuanba area were studied, and the effects of the pore structure of shale on the occurrence state of shale gas were discussed. Inorganic pores (76.92%), organic pores (9.17%), and microfractures (13.91%) are developed in the shale. Among them, the inorganic pores are mainly clay mineral pores formed during the smearing of montmorillonite. The organic pores are underdeveloped. The reason is related to the fact that the type of organic matter is mainly type III and the TOC content is low. In the whole-aperture pore size distribution of shale pores, the micropore, mesopore and macropore contributed 6.76%, 76.92% and 16.30% of pore volume espectively. It can be seen that the shale in the Da''anzhai member of the Yuanba area is dominated by inorganic pores, mainly meso-macropores, together with the high temperature and high pressure of the reservoir controlled the occurrence of shale gas in this area is mainly free gas.