Abstract：In order to study the effect of different solvents in the combined fracturing fluid on the surface property and pore sturcture of high rank coal, coal samples from Changzhi were extracted or dissolved in different orders by combined solvents, including organic solvent (THF) and inorganic acid (HCl) , organic solvent (CS₂) and strong oxidant (ClO₂) . By means of contact angel and low temperature liquid nitrogen adsorption experiments, the characteristics of surface property and porosity changes during the process of solvent disposition were comparatively studied. The results showed that the yields of solvent extraction (dissolution) in the sequence of organic solvent and inorganic solvent disposition was higher than that of inorganic solvent and organic solvent, and the extraction yield of organic solvent was much higher than that of inorganic solvent. With the coal-water contact angel decreasing, the surface tension and hydrophily for the HCl treated coal increased. all the individual changes to organic solvents and ClO₂treated coal were reversal. After the disposition of different solvents, the BET specific surface area and BJH specific pore volume of coals increased significantly, and the increase of organic solvent and inorganic solvent disposition of coals was larger than that of inorganic solvent and organic solvent. All of the solvents used in the experiment had pore-expanding effect, especially for the pores with smaller diameter. By comparison, the reconstruction effect on the pores with two kinds of solvents disposition was better than that with one kind of solvent disposition for coals. For the combined solvents, CS₂and ClO₂had the most significant reconstruction effect on pores, while the result of THF and HCl was not obvious. Therefore, the solvents of CS₂and ClO₂as pre-fluid or carrying fluid of fracturing fluid would have better reconstruction effect on coal reservoir.

Keyword：combined solvent;fracturing fluid;high rank coal;surface property;pore structure;