Gas storage in shale primarily includes three forms: free gas in the fractures or macropores, adsorbed gas upon the kerogen surface, and absorbed gas in the kerogen matrix. However, current techniques cannot distinguish the adsorbed and absorbed gas, which restrict the understanding of gas storage and transport mechanisms through shale kerogen. On the basis of the grand canonical Monte Carlo (GCMC) simulations, we propose a technique to determine the independent adsorption and absorption isotherms of methane within slit-shaped shale kerogen under supercritical conditions. We observe that if the pore pressure is higher than ~3.5 MPa, the absorption amount is much smaller than that of adsorbed gas; however, at lower pressures, the absorption capacity is superior to that of the adsorption. Meanwhile, the ratio between adsorption and absorption quantities continuously increases with pressure. We probe the underlying mechanisms and study the effect of slit aperture, temperature, as well as moisture on gas adsorption and absorption capacity. Enlarging the slit aperture increases the adsorbed gas contents but shows only a negligible effect on the absorption capacity. Heating facilitates the escapement of gas molecules, thus leading to the inhibition of both adsorption and absorption capacities. Water molecules occupying the adsorption site on the slit surface impedes methane adsorption, but the absorption capacity within the kerogen matrix remains unchanged. This work elucidates the gas adsorption and absorption behavior in shale kerogen and sheds light on the storage and transport of hydrocarbons in nanoporous materials.

页岩中的储气主要包括三种形式：裂缝或大孔中的游离气体，干酪根表面上的吸附气体和干酪根基质中的吸附气体。但是，当前的技术无法区分吸附和吸收的气体，这限制了对通过页岩干酪根的储气和输运机理的理解。在大经典蒙特卡洛（GCMC）模拟的基础上，我们提出了一种确定超临界条件下缝状页岩干酪根中甲烷的独立吸附和吸收等温线的技术。我们观察到，如果孔隙压力高于〜3.5 MPa，则吸收量远小于吸附气体的吸收量。但是，在较低的压力下，吸收能力优于吸附能力。与此同时，吸附量和吸收量之比随压力连续增加。我们探究了潜在的机理，并研究了狭缝孔径，温度以及水分对气体吸附和吸收能力的影响。增大缝隙孔径会增加吸附气体的含量，但对吸收能力的影响仅可忽略不计。加热促进气体分子的逸出，从而导致吸附和吸收能力的抑制。占据狭缝表面上吸附位点的水分子阻碍了甲烷的吸附，但是干酪根基质内的吸收能力保持不变。这项工作阐明了页岩干酪根中的气体吸附和吸收行为，并为纳米多孔材料中碳氢化合物的储存和运输提供了启示。