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Pore characteristics heavily influence the gas storage mechanisms in gas shales. For a deep understanding of the pore structure characteristics, the fractal analysis was performed through low-pressure nitrogen (N 2 ) adsorption experiments on 5 shale samples collected from Gondwana and Assam basins of India. The characteristics of low-pressure N 2 adsorption isotherms revealed the mesoporous nature of the shale samples. It can be observed that N 2 adsorption was dominated by van der Waals forces until the relative pressure (P/P o ) reached ≈0.45, and later, it was dominated by surface tension thereby dividing the adsorption curve into 2 regions at P/P o ≈ 0.45. Fractal dimensions (D) were estimated using the Frenkel−Hasley−Hill (FHH) method in the abovementioned 2 regions separately. The fractal dimensions were further correlated with the shale constituents and different pore characteristic parameters. Results indicate that fractal dimensions are positively correlated with the BET specific surface area (BET-SSA) and quartz content. However, fractal dimensions negatively correlated with the TOC, CO 2 micropore volume, and average pore diameter. Comparison of the fractal dimensions with the shale pore characteristics suggested that the selected shale samples are highly nonhomogeneous and are dominant with complex micropores and mesopores.

Shale gas exploration has gained tremendous attention worldwide, because of the successful development and progress in exploitation technology in the North American and Chinese basins. Since organic-rich shales are good sources of gas, and thick layers of such shales are present worldwide, significant potential exists for countries with such reservoirs. For efficient exploitation of shale gas reserves, a thorough understanding of the methane storage mechanism is required. Several physico-chemical–mechanical factors, along with heterogeneity in shales influence the storage mechanism, and add to the complexities of the unconventional hydrocarbon reservoir. Thus, a systematic investigation is essential to explore the nature of shale, and to assess the factors influencing their gas storage capacities. Among other factors, organic matter content is considered to be a crucial factor for gas storage and transport. This paper attempts to critically review the pore attributes of the organic matter present in shale by a thorough assessment of scientific articles. We comprehensively describe the factors that affect the behaviour of shale that lead to the differences in pore characteristics. This paper highlights shale as an adsorbent; explains the different gas adsorption isotherm types, adsorption thermodynamics, and molecular simulation of methane sorption behavior in kerogen. Additional factors that influence the organic pore characteristics (total organic content, kerogen type, and thermal maturity) have been critically reviewed and discussed. Finally, the article highlights the dependence of these factors along with moisture and temperature, on shale’s methane sorption capacity. The article points out the research gaps in the field, while discussing experimental protocols of gas adsorption analysis. Future suggestions for understanding the methane sorption capacity in shales are also provided.

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