Enhanced Explosion Characteristics of Methane/Air Induced by Barium Nitrate under a Large Horizontal Pipeline

High explosion pressure is desired for fracturing shale to extract shale gas. In this work, the role of barium nitrate (Ba-(NO₃)₂) in enhancing the explosion characteristics of CH₄-O₂-N₂ mixtures by a 500 L horizontal pipeline has been explored. First, the key factors that influence explosion characteristics, including particle size and loading amount, have been studied. It is found that there exist two optimum formulations under which the explosion overpressure can be enhanced significantly. They are particle diameters of 65.3 and 29.2 μm corresponding to loading amounts of 100 and 75 g, respectively. Furthermore, the effects of different equivalence ratios under the two optimum formulations and the underlying improved mechanisms of Ba-(NO₃)₂ have been probed. The results demonstrate that the loading approach of spraying Ba-(NO₃)₂ into methane not only enhances the explosion overpressure and average pressure rise rate but also greatly shortens the pressure rise time. Besides, the pure experimental gas reaches its maximum overpressure when the equivalence ratio of methane is 1, whereas the maximum overpressure after adding Ba-(NO₃)₂ is attained at a methane equivalence ratio of 1.25. Given a methane concentration of 13% and an equivalence ratio of 1.25, a maximum explosion overpressure of 22.52 MPa with an average pressure rise rate of 2.104 GPa/s has been achieved. These findings provide methodological and data support for the development of explosive fracturing technology in horizontal and vertical wells.