基于氮气吸附实验的页岩孔隙结构表征

页岩储层微观孔隙结构研究对页岩含气性评价具有重要意义。为此，采用低温氮气吸附法，对宁夏六盘山盆地下白垩统乃家河组页岩样品的微观孔隙结构进行了实验研究，计算了页岩的比表面积、孔径分布、孔体积和平均孔径等孔隙结构参数，并探讨了页岩孔隙发育的控制因素及孔隙结构对页岩气存储的意义。实验结果表明：①页岩平均孔径为3.6~4.3 nm，主体孔隙为中孔，也含有一定量的微孔和大孔，孔隙形状以平行板状和墨水瓶孔为主，同时具有无定形孔特征；②页岩比表面积和孔体积远大于常规储层岩石，孔径小于50 nm的微孔和中孔提供了主要的比表面积和孔体积，构成了页岩中气体吸附存储的主要空间；③页岩微孔、中孔的发育与有机质有关，有机碳含量与微孔、中孔的比表面积、孔体积呈正相关性，页岩大孔的发育与黏土矿物含量有关，黏土矿物含量增加，大孔的比表面积和孔体积都增大。

Characterization of pore structures in shales through nitrogen adsorption experiment

The study of micro pore structures is of great significance to the assessment of the gas bearing property of shale reservoirs. In view of this, by use of the low temperature nitrogen gas adsorption method, an experimental study was performed of the micro pore structure of shale samples from the lower Cretaceous Naijiahe Formation, Liupanshan Basin, Ningxia. In this case study, the specific surface area, pore size distribution, pore volume, average pore diameter, etc. were all calculated; a discussion was then made on how the controlling factors of shale pore development and the pore structure take effect to the storage and preservation of gas in shales. The following findings were obtained. a. The average pore diameter of shales ranges from 3.6 to 4.3 nm; there are mostly mesopores while some micro and macro pores also exist; there are two main pore types in shales, including slit like and inkbottle like pores, and some of the pores are amorphous. b. The specific area and pore volume of shales are far greater than those of conventional reservoir rocks; the micro and meso pores with the pore diameter smaller than 50 nm provide the dominating specific area and pore volume, which constitute the major space for gas adsorption and storage in shales. c. The organic matter in shales is an important control on micro and meso pores, shown by positive correlations between the total organic carbon (TOC) content and the specific area and pore volume of micro and meso pores; macropores are associated with clay minerals, i. e., the more the content of clay minerals, the greater the specific area and pore volume of macropores.