Effects of wettability differences of different macroscopic composition of coal on methane adsorption and desorption

The wettability of coal reflects the interaction between coal and water,and is also an important factor affecting methane adsorption/desorption. The wettability differences of vitrain and durain of No.4 coal seam in the Dafosi coal field their influence on methane adsorption/desorption are analyzed,based on the data of wettability and methane adsorption/desorption test. The results show that the contact angle between coal and water is less than 90°,indicating the coal is hydrophilic,which of vitrain is 66.9°and durain is 61.2°. The wettability of durain is better than vitrain. The wettability sequence of coal samples treated by different active agent solutions is G502 samples (hydrophobicity),6501 samples,LAS samples and JFC samples,from poor to good. G502 promotes the wettability reversal of coal,resulting in the contact angle of vitrain and durain increased to 98.8° and 90.3°,respectively. And the other three active agents can improve the wettability of coal samplesresulting in the contact angle reduced to 32.5°. Compared with durain,vitrain has relatively more micropores,with a proportion of 80%,poor pore connectivity and wettability,strong methane adsorption capacity and lower methane desorption efficiency. The wettability of coal is negatively correlated with methane adsorption capacity,ranging from 5.63 to 26.98 cm3/g and the adsorption capacity from strong to weak is G502 sample,air dried sample,water balanced sample,6501 sample,JFC sample and LAS sample. The desorption capacity was positively correlated with the wettability,and the desorption capacity from low to high was G502 sample,6501 sample,JFC sample and LAS sample. The better the wettability of coal,the stronger the coal-water interface molecular interaction,and the coal matrix surface is easier to be occupied by a large number of water molecules,thus the coal methane adsorption capacity is weakened because of competitive adsorption of water and methane molecules,but that also promote methane desorption.