Mechanisms of shale gas adsorption: Insights from a comparative study on a thermodynamic investigation of microfossil-rich shale and non-microfossil shale

Effect of Pre-Adsorbed Water on Methane Adsorption Capacity in Shale-Gas Systems

“…It is obvious that Langmuir volume is negatively correlated with temperature, to put it differently, the maximum methane adsorption capacity of shale reduces with temperature. This negative relationship is highly consistent with the conclusions of previous studies (Ji et al, 2015;Tian et al, 2016;Chen et al, 2017b;Li et al, 2017) and is largely owning to the exothermic process of methane adsorption on shale (Chen et al, 2019b;Hu et al, 2021).…”

“…Previous studies have found that methane molecules are adsorbed to a large extent on the pore surface of organic matter and clay minerals rather than other minerals (Merkel et al, 2015;Yang et al, 2015;Ju et al, 2019;Zhu et al, 2020), and the contribution of organic matter almost doubles that of clay minerals (Yang et al, 2015). Furthermore, due to strong hydrophilicity of clay minerals, their adsorption capacity for water molecules exceeds that of organic matter (Zolfaghari et al, 2017;Chen J. et al, 2021). Based on discussions above, distinctive adsorption mode of methane molecules in shale were constructed in Figure 5 for organic matter and clay minerals in both low and high water saturations.…”

“…It is important to note that the amount of methane adsorbed in the experiments is the surface excess adsorption amount, not the absolute or actual adsorption amount. Therefore, conversion from excess adsorption to absolute adsorption is required for the evaluation of shale gas adsorption capacity (Rexer et al, 2013(Rexer et al, , 2014Yang et al, 2017;Zhou et al, 2018;Chen L. et al, 2021). To simplify the calculations, the liquid density of methane at boiling temperature and ambient pressure (0.421 g/cm 3 ) was used as the adsorbed phase density for the methane excess adsorption correction.…”

“…In addition, since organic matter tends to absorb more methane molecules than water molecules (Tian et al, 2020;Sun et al, 2021), its methane molecules concentration at low water saturation is higher than its water molecules concentration at high water saturation. Likewise, as clay minerals are more prone to adsorb water molecules (Zolfaghari et al, 2017;Wang T. et al, 2019;Chen J. et al, 2021), its water molecules concentration at high water saturation is higher than its methane molecules concentration at low water saturation.…”

“…Tian et al (2020) investigated the influence of pore water on the gas storage of organic-rich shale and pointed out that the adsorption space of methane onto clay mineral sufaces in microand mesopores is occupied by water, which results in a decrease of adsorbed gas, and the occurrence of adsorbed gas is dominated by organic matter adsorption. In addition, some scholars have also investigated the influence of water on methane adsorption through molecular simulation and found that water has an important effect on methane adsorption (Huang et al, 2018;Li et al, 2019;Chen G. et al, 2021).…”