Experimental study on effects of tetrahydrofuran soaking on pore structure and gas adsorption and desorption characteristics of coal

The extraction effect of organic fracturing fluids when used to soak coal can change the pore structure in coal while influencing the adsorption and desorption characteristics of coal. Tetrahydrofuran (THF) was selected as a typical organic fracturing fluid to analyze quantitatively the pore parameters in the full aperture section of coal combining approaches including CO2 adsorption, low-temperature nitrogen adsorption (LNA), and high-pressure mercury intrusion porosimetry (MIP). Results show that the reconstruction effects of THF soaking on pore structure include the following four aspects: (a) generating new pores; (b) connecting originally disconnected pores; (c) turning closed pores into opened or semi-opened ones; and (d) blocking pores. The improved hysteresis index (IHI) for desorption of coal samples is 0.14629 0.54799, while it always decreases after THF soaking (by 38% 62%). The results provide theoretical support for revealing the mechanism by which the organic fracturing fluid enhances the CBM migration.