Surface microtopography and micromechanics of various rank coals

For a long time, coalbed gas has brought about various problems to the safety of coal mine production. In addition, the mining of gas and coalbed methane (CBM) has attracted much attention. The occurrence and migration of CBM are believed to be closely related to the micro-surface properties of coal. To further explore the characteristics of CBM occurrence and migration, in this study, the micro-surface topography, adhesion, and elastic modulus of five metamorphic coals were measured by atomic force microscopy (AFM). The results show that the microtopography of coal fluctuates around 40 nm, reaching a maximum of 66.5 nm and the roughness of the surface decreases with the increase of metamorphism. The elastic modulus of coal micro-surface varies from 95.40 to 9626.41 MPa, while the adhesion varies from 15.08 to 436.22 nN, and they both exhibit a trend of M shape with the increase of metamorphism. Furthermore, a high correlation exists between adhesion and microtopography fluctuation. In most cases, the adhesion is larger in the concavity area and smaller in the convexity area. The research results may provide a new method for revealing the occurrence and migration of CBM and ensure efficient and safe CBM exploitation.