Pore Volume Characteristics of Clay-Rich Shale: Critical Insight into the Role of Clay Types, Aluminum and Silicon Concentration

Shale resources contain a significant quantity of clay minerals and organic matter. These material components influence the evolution of intra- and inter-granular pore features. This study investigates the role of clay’s elemental concentration, purity and types on its pore attributes. Four samples; illite, chlorite, montmorillonite, and kaolinite-rich clay samples were studied. Clay elemental composition, purity, pore shape, and structural parameters were determined. X-ray fluorescence and diffraction techniques were used to compute the elemental and mineralogical compositions of clay samples, respectively. Rock surfaces were mapped using the energy dispersive x-ray spectroscopy and scanning electron microscopy to confirm the distribution of elements and clay homogeneity, respectively in the four phyllosilicate materials. Total organic content analysis confirms the quantity of organic matter. N₂ adsorption/desorption experiment at 77 K and over a relative pressure range up to 0.995 was executed with a surface area and porosity analyzer, to extract information regarding the pore shape, and determine the pore volume and specific surface area. The interrelation of the purity and computed pore structure properties was established. Mineralogy and elemental analyses showed that the studied samples with clay purities of 60–98% have a combined 80–96 wt.% of Aluminum (Al), Silicon (Si), and Iron (Fe). The adsorption–desorption curve at p/ p^o< 0.04 and carbon content analysis indicate that clays accommodate negligible micropores. The type III and IV isotherms combined with H1, H2, and H3 hysteresis loop implied that clay had connected complex pores with plate-like, uniform cylindrical, and inkbottle shapes. Capillary condensation and evaporation curves revealed more mesopores and macropores of 2-50 nm and > 50 nm, respectively. The pore distribution plateaued around an average of 100 nm, which confirmed the suitability of the Barrett-Joyner-Halenda technique to characterize clay mesopores. Kaolinite has the highest capacity (74.43 cm ³/g) to host N₂ gas at a standard temperature and pressure followed by montmorillonite (65.08 cm ³/g), chlorite (21.01 cm ³/g) and illite (16.59 cm ³/g) in that order. The capacity of the pores to store fluid and their average size follow a similar pattern and increase with aluminum and clay contents. A specific surface area of the non-micropores is directly related to silicon concentration. The study provides an insight regarding the potential of kaolinite (with the highest aluminum concentration of 39.5 wt.%) as a good catalytic material required to speed up the esterification reaction. In addition, it can serve as a waste repository and a material for the treatment of phosphorus-containing contaminants in polluted areas. This research confirms that montmorillonite with the largest specific surface area in non-micropores and silicon content of 63.9 wt.% promotes reactivity and cation exchange interaction. However, this high basal spacing attribute of the material means that swelling will occur in the presence of water.