In this study, coal and shale samples were collected from the gas-rich Barakar Formations and investigated using various analytical and imaging methods, to quantify their pore attributes. The results indicate that coal contains an abundance of nanopores that occur in clusters, along with evidence of microfractures in its structure, as observed through scanning electron microscopy (SEM). The accessible micropore surface area (SA) of coal samples is around 2.5 times higher than that of shale samples, while the total mesopore SA in coal is around half that of shales. However, the average pore width of coal samples is approximately 0.82 times that of shale samples. These findings suggest that a higher percentage of organic carbon in coal contributes to an abundance of organic pores, which results in greater porosity in coal samples when compared to shale. The total SA determined by gas adsorption for the entire spectrum of pore sizes in coal is around two times that of shale. Interestingly, despite the difference in the pore SA and the pore volume, the pore surface roughness in the studied coals is almost equal to or slightly higher than that of shales. The study observations show that the total organic carbon and mineral composition in coal and shale play little influence on the degree of pore connectivity. The degree of pore connectivity for the coal samples varies from 0.4–0.93, whereas for shale samples it ranges from 0.50–0.82. This study provides analytical insights into the pore structure of coal and shale collected from the same reservoir by considering factors such as depth, mineralogical content, and surface roughness. During CO2 injection, coal and shale reservoirs may experience swelling induced stress changes, potentially impacting their mechanical stability. Thus, this study provides insight into estimating the gas-storage capacities of both coal and shale reservoirs and aims to optimise the gas adsorption and maintain structural integrity. This approach ensures the long-term feasibility of implementing Enhanced Coalbed Methane (ECBM) recovery and shale gas recovery in other gas basins.

Lithologically diverse shales were collected from two different proliferous basins, namely, the Korba (SM) and Raniganj Basin (BK) in India, and were experimented with at an isothermal condition using CO₂ and N₂ as probe gases in the low-pressure gas adsorption method, demonstrating the disparity between shale pore attributes and surface roughness. The Korba Basin is one of the potential sites for gas storage and production in India and needs to be explored in terms of pore statistics. Literature reviews demonstrate that pore characteristics in shale changes with depth, organic matter, and mineral composition, which can elucidate the gas storage potential for anthropogenic CO₂ storage. Gas adsorption capacity and surface roughness are directly associated with the difference in organic and mineral compositions, which certainly affects the phase distribution of flow regimes in shale reservoirs. The result determines that micropore and mesopore attributes are in good correlation with the TOC and clay minerals, respectively. SM shale shows 30-37% higher micropore attributes and 17-19% lower mesopore attributes than those of BK shales. Furthermore, the siderite content shows a variance in the pore size distribution in BK shales. The fractal dimension (D_s) is evaluated based on the N₂ adsorption isotherm curve using the Frenkel-Halsey-Hill model. SM shales show a strong correlation with both micropores and mesopores at low relative pressure regimes, while BK shales depict their dominance with mesopores at the high relative pressure regime. Therefore, this research provides a preliminary attempt to determine the influence of changes in the depth, surface roughness, and organic and mineral compositions on shales. However, a complete extrapolation of other reservoir factors, viz., seam thickness, shale-water interaction, and permeability variation at reservoir conditions, is vital to unlocking the technical and environmental feasibility of CO₂ storage and gas production in these basins.

A combination of high-resolution imaging, low-pressure gas adsorption, and small-angle X-ray and neutron scattering quantifies changes in the pore characteristics of pulverized shale samples under oxic and anoxic environments up to 300 ℃. Clay-rich early-mature shales have a fair potential to generate hydrocarbons, the total organic carbon content of which lies within a range of 2.9 % to 7.4 %. High-resolution imaging indicates restructuring and coalescence of Type III kerogen-hosted pores due to oxic heating, which causes up to 580 % and 300 % increase in the surface area and pore volume of mesopores respectively. Similarly, up to 300 % and 1200 % increase in micropore surface area and pore volume is observed post oxic heating. However, during anoxic heating, bitumen mobilizes, leads to pore-blockage, and reduces the surface area and pore volume up to 45 % and 12 % respectively without any significant mass loss up to 350 °C. Between 400 and 550 °C, considerable loss in mass occurred due to breaking of organic matter, facilitated by the presence of siderite that caused up to 30 % loss in mass. The test conditions display starkly opposite effects in pores that have a width of < 100 nm when compared to the larger macropore domain, which has a pore width in the range of 100 to 700 nm as inferred from their small-angle X-ray (SAXS) and neutron (SANS) scattering behaviour, respectively. Despite the formation of new mesopores or the creation of new networks of pores with rougher surfaces, the fractal behavior of accessible mesopores in combusted shales minimally increase mesopore surface roughness. The pyrolyzed shales exhibit decreased mesopore surface roughness at higher temperatures, which indicates smoothening of pores due to pore blocking. Increase in pore volume and surface area due to oxic-heat treatment enhances the feasibility of long-term CO₂ storage in shales.