Evolution Characteristics of the Microstructure with Different Fracturing Fluids: An Experimental Study of Guizhou Bituminous Coal

[Image: see text] Fracturing fluid is a key factor affecting the hydraulic fracture morphology and coal microstructure, which plays a key role in the hydraulic fracturing effect. To compare the effect of clean water, clean fracturing fluid, and acid fracturing fluid on the pore structure of coal, this paper used high-pressure mercury injection (MIP), low-temperature N(2) adsorption (LT-N(2)A), and scanning electron microscopy (SEM) to determine the pore structure of Guizhou bituminous coal before and after the action of fracturing fluid. The results show that clean water can cause mineral expansion and reduce pore volume by about 6% and clean fracturing fluid and acid fracturing fluid can increase pore volume by 3 and 12%, respectively, due to different degrees of acidity. The MIP data show that the pore structure of coal samples is more complex after the action of different fracturing fluids, and acidic fracturing fluids can increase the fractal dimension of the pore by about 7%. The LT-N(2)A data showed that the fractal dimension of micropores and transition pores decreased after the action of different fracturing fluids. In general, acid fracturing fluid has the best effect on the coal microstructure, followed by clean fracturing fluid, and the least effect on clean water.