海陆过渡相页岩孔隙结构特征及分形维数研究

页岩孔隙结构的研究是页岩储集性及含气性评价的重要方面。运用低温氮气等温吸附实验对龙潭组页岩储层的孔隙特征进行了测定,通过孔隙分形维数的计算结合岩石矿物组分、有机质含量及热成熟度测试探讨了龙潭组页岩孔隙结构特征及影响因素。分析结果表明:龙潭组页岩孔隙结构复杂,孔隙类型包括一端封闭型的不透气孔、开放型平行板状狭缝及墨水瓶状孔,平均孔径分布在5.38~13.3 nm,平均为7.78 nm,孔径分布呈双峰型分布的特征;孔隙分形特征明显,分形维数在2.49~2.62,平均为2.54;分形维数受有机质特征、矿物成分及孔隙结构特征共同影响,具体表现为分形维数随TOC(有机碳含量)、R_O、黏土矿物含量及比表面积的增加而增大,随长石含量及样品的平均孔径的增加而减小,与石英及其他矿物成分无明显的相关性。

Study of pore structure characteristics and its fractal dimensions of transitional shales

The study of pore structure of shales is considered as a significant part in the evaluation of reservoir properties and gas content of gas shales. In this study, low temperature nitrogen adsorption experiment was conducted to determine the pore characteristics of shales in Longtan Formation, in addition, a further study of pore structure and its controlling factors were investigated through the calculation of fractal dimensions of the pore combined with tests such as mineral composition, organic matter content and thermal maturity. The results show that the Longtan shales have a relatively complicated pore structure, which consist mainly of airtight pores closed at an end, open parallel plate silts and ink-bottle pores. Pore diameters vary from 5.38~13.3nm and 7.78nm on the average which show a bimodal patterns in terms of pore size distributions. The Longtan shales show significant fractal characteristics, of which the fractal dimensions range from 2.49~2.62, and 2.54 on the average. There is closely correlation between the fractal dimensions and organic matters, mineral compositions and pore structure, as is proved by the fact that fractal dimensions increase with TOC content, RO, total clay content and specific surface areas, while decrease with feldspar content and average pore diameter and no correlation is found between them and quartz, neither do other minerals.