Microstructural Changes of Pulsating Hydraulic Fracturing Coal Seam and Its Engineering Practice

To study the microstructure changes of the pulsating hydraulic fracturing coal seam, this paper conducts a laboratory test of pulsating hydraulic fracturing from the coal samples of Yangliu, Guqiao and Dingji coal mines. And the development rules of pore characteristics of original samples and samples under hydraulic fracturing were analyzed through mercury injection experiment and CO₂ gas adsorption testing. The results show that the pore connectivity in macro-pore phase is significantly better than that in the mesopore stage. And the porosity, micro-pore ratio, total pore volume and total surface area increase with the increase of coal rank. The mesopore ratio decreases as the coal rank increases, and macro-pore ratio has the trend of “decrease-increase” with the increasing of coal rank. After the pulsating hydraulic fracturing, the porosity increases significantly, however, water has no effect on the pore connectivity. Pulsating hydraulic fracturing reduces the total pore surface area, micropore volume and micropore ratio of the coal sample, while the mesopore ratio, macro-pore ratio and the total pore volume increase.