Study on wettability and influencing factors of different macroscopiccomponents in low rank coal

With the deepening of the exploration and development of low rank coalbed methane in China, problems such as low gas content, low reservoir pressure and high water content have become increasingly prominent. In order to study the difference in wettability of different macro-coal components in low-rank coal and its influencing factors, this paper takes the No.4 coal mine of Dafosi Coal Mine in Huanghua coalfield as the research object, and collects the whole-layer coal sample, mirror coal sample and dark coal sample, and measures the contact. The differences in wettability were analyzed by angle comparison and the effects of industrial composition, chemical structure and pore characteristics on wettability were discussed in detail. The contact angle of No.4 coal in Dafosi Coal Mine is 45.8° to 60.4°, both of which are less than 90°, showing strong hydrophilicity. The contact angle of mirror coal is larger than that of dark coal, and the wettability of dark coal is better. The properties are related to the direction of the bedding.The order of wettability from high to low is: vertical bedding direction, oblique bedding direction, parallel bedding direction. Surfactant 6501 can effectively enhance the wettability of coal. Its modification effect on mirror coal is greater than that of dark coal, and the modification effect on parallel bedding direction is greater than that in vertical bedding direction. Both the material composition and pore structure of coal have a significant effect on its wettability. Inorganic minerals (ash) are hydrophilic: the higher the ash content is, the better the wettability of coal will be. And the volatiles are usually hydrophobic, the higher the volatiles are, the worse the wettability of coal will be. Compared with durain, vitrinite has lower ash content and higher volatile content, resulting in its worse wettability. The higher content of H element is, the poorer wettability will be, and the effect of C and O elements on wettability depends on the type of oxygen containing functional groups. Durain contains more polar oxygen containing functional groups such as hydroxyl and carboxyl, favorable for wettability, whereas vitrain contains more nonpolar oxygen ether and ester bond. Compared with dark coal, the pores of mirror coal are mainly semi-closed pores, with poor connectivity, poor sorting, small pore size, large specific surface area and rough surface, which makes the wettability worse.