Effects of acid fracturing fluid on dynamic fracture behavior and energy dissipation characteristics of anthracite coal
To investigate the effect of acidic fracturing fluid on the fracture behavior and energy dissipation of anthracite under impact load,a split Hopkinson pressure bar(SHPB)impact loading system was used to conduct model-Ⅰ dynamic fracture toughness tests on notched semi-circular bending(NSCB)anthracite samples treated with acidic fracturing fluid and water-based fracturing fluid under varying impact pressures.The dynamic crack propagation process of coal samples was recorded by high-speed camera device.Combined with Image J analysis software and PCAS image recognition system,the macroscopic crack propagation trajectory and probability entropy of micro pores in coal samples were quantitatively analyzed.By comparing the incident energy,absorbed energy,fracture energy and residual kinetic energy of anthracite samples under different impact pressures and various fracturing fluids,the energy dissipation law of dynamic fracture process of acid corroded coal samples under impact loads was obtained.The results show that the dynamic fracture toughness of coal samples in natural state is the largest,and the fracture toughness of coal samples treated with acid fracturing fluid is lower than that of water-based fracturing fluid when the impact pressure is higher than 0.35 MPa.The prefabricated cracks in acidic fracturing fluid-treated coal samples are more likely to initiate under higher loading air pressure conditions.The difference between the fracture energy required by acid fracturing fluid group and that of water-based fracturing fluid group increases with the increase of loading pressure.The higher the loading air pressure,the less fracture energy required for the acid fracturing fluid treated coal samples compared to the water-based fracturing fluid group.The pore probability entropy value of coal sample fracture surface increases with the increase of impact pressure,and the fracture surface morphology of coal sample transforms from compact and neat to loose and porous due to the action of acid fracturing fluid.The dual mechanism of weakening and enhancing the fracture behavior of anthracite coal by fracturing fluid under different loading rates was explored,and a microscopic fracture mechanics model considering the loading rate was established based on the dual nature of fracturing fluid and the theory of linear elastic fracture mechanics.The research results provide experimental support for the investigation of crack initiation and propagation mechanism of acid fracturing for anthracite coal,and provide theoretical guidance for the design of acid fracturing in coal seam and the control method of complex fracture network.
rock mechanicsanthracitefracture toughnessacid fracturing fluidcrack propagationenergy dissipation
NETL
NSTL
万方数据
