Multiscale Pore Analysis of Unconventional Resources from the Barakar Formation using Fluid-Invasive,  Scattering and Imaging Methods.

This study investigates unconventional resources such as coal and shale belonging to the Barakar Formation. Various analytical methods such as fluid invasive low-pressure gas adsorption (LPGA) and mercury intrusion porosimetry (MIP), small angle x-ray scattering (SAXS) and imaging methods were employed to determine the pore attributes and pore characteristics of coal and shale. The results show that coal has an abundance of nanopores that occurs in clusters, having evidence of microfractures in its structure, as observed through scanning electron microscopy (SEM). It was found that the accessible micropore surface area (SA) of coal samples is approximately 2.5 – 3 times that of shale samples, while the accessible and inaccessible mesopore SA in coal is about half of that in shale. Nevertheless, the average pore width of the coal samples is around 0.8 – 0.9 times that of the shale samples. These results suggest that the coal has a higher percentage of organic carbon that contributes to the abundance of organic pores, that leads to higher porosity in coal samples compared to shale samples. The total SA, incorporating the entire spectrum of pore sizes, is about 2 times as large in coal as in shale. Interestingly, despite disparity in pore SA and pore volume, the pore surface roughness in coal is nearly equal to or slightly higher than that of shale. The study provides a detailed analysis of the pore structures of unconventional resources, such as coal and shale from the same reservoir, considering various parameters such as depth, mineralogical  content and surface roughness. During CO2 gas injection, the coal and shale formations may experience change in geomechanical responses, potentially compromising their mechanical stability. Furthermore, any loss to the caprock integrity could result in leakage and reservoir failure. Thus, this study is critical for estimating the secure CO2 storage capacity of coal and shale reservoirs. The findings aim to optimize gas adsorption while maintaining structural stability, ensuring the long-term feasibility of CO2 sequestration in other basins.