Effect of a newly synthesized anionic Gemini surfactant composite fracturing system on the wettability of coking coal

To improve the wetting effect of the fracturing fluid on coal, a sulfonate Gemini surfactant (Gemini-3OH) was synthesized from nonyl phenol through a double ether and sulfonation reaction. It was mixed with an appropriate amount of cationic cellulose (JR400) to form a fracturing fluid composite system (Gemini-3OH/JR400). The optimum concentration ratio of the composite system was determined using a surface tension test. The mechanism of action of water, Gemini-3OH and Gemini-3OH/JR400 composite system on the coal surface was analyzed by means of FTIR, XPS, industrial analysis, and SEM, along with microscopic observations, contact angle measurements, and molecular dynamics simulations. The results showed that Gemini-3OH/JR400 had a lower critical micelle concentration and surface tension, and had the greatest impact on the coal structure and functional group content. The contact angles of Gemini-3OH/JR400 at the moment of contact with coal and at 60 s were 33.12° and 19.76°, respectively. Finally, molecular dynamics simulations further verified that Gemini-3OH/JR400 had a better wetting effect on coal. This study provides a new concept for wetting coal bodies by water injection and fracturing in coal seams, and hence, can help in the prevention and control of mining accidents and disasters.