Experimental Research on the Performance of a Wetting Agent Based on Compound Acidification in Low-Porosity and Hard-to-Wet Coal Seams

[Image: see text] To improve the wetting performance of the composite acid solution in the deep coal seam, in this paper, the surface tension and contact angle characteristics of the compound acid wetting agent are studied, then the composition of the wetting agent is developed and evaluated based on nuclear magnetic resonance. The research indicates that surfactants can reduce the surface tension of water, and the surface tension tends to decrease with the increase in the surfactant concentration. The critical micelle concentration of the anionic surfactant sodium dodecyl sulfate (SDS) solution is only 0.025%, and the corresponding critical surface tension is 30.63 mN/m. The wetting agent material based on the composite acid solution includes the acid HCl, HF, the anionic surfactant SDS, and the inorganic salt NaCl, the composition of which is 8%, 8%, 0.025%, and 0.6 mol/L, respectively. The total wetting rate of the composite acid-containing HCl + HF + SDS + NaCl is the largest, reaching 64.30%, which has good wettability inside the coal and can be a comprehensive intrusion into the internal structure of coal pores.