Contribution and Coupling Effect of Adsorption on Clay Minerals and Organic Matter in the Early Diagenetic Stage of Coal Measures

In this study, the pore characteristics and the factors of maximum methane adsorption capacity (MAC) of mudstone in the early diagenetic stage (EDS) and the contribution rate of clay mineral (CM) adsorption were analyzed. In addition, the adsorption coupling effect of CM and organic matter (OM) was discussed. Studies have shown that pores of coal measure mudstone in the early diagenesis stage are mainly small pores with slanted platelike staggered and overlapped pores, with more pore opening directions. The main controlling factors of the maximum MAC of mudstone are OM and CM, and the direct expression is the pore surface area. In the EDS, the contribution rate of CM in mudstone is lower, while the contribution rate of OM to the MAC of mudstone is higher. There is an adsorption coupling effect of CM composition and OM. OM in mudstone is scattered, and the CMs have a supporting effect, which leads to OM in mudstone having a large contact area with the open space and has many effective pores. OM in coal is concentrated, and the surface area of OM per unit volume is small (compared with OM in mudstone). The compaction and deformation characteristics of CMs have a plugging/sealing effect on the pores of OM in the coal, which makes the effective pores of OM per unit volume in coal lower than those in mudstone.

Automated summary

This study analyzed the pore characteristics and factors affecting the maximum methane adsorption capacity (MAC) of mudstone in the early diagenetic stage, as well as the contribution of clay mineral (CM) adsorption. The main controlling factors of MAC were found to be OM and CM, with a significant adsorption coupling effect between them. Additionally, the contribution rate of CM in mudstone was lower, while OM had a higher contribution rate to MAC. This study highlights the importance of considering both OM and CM when studying methane adsorption in mudstone during early diagenesis.