Coupled loading simulation for combined pulse fracturing and the sensitivity analysis of different propellant ratios

In the present study, based on the physical process of combined pulse fracturing, we proposed a model for the coupling of the whole process of multi-pulse conflagration fracturing using different combinations of the multi-level pulse propellant conflagration loading model, the pressurized liquid column movement model, the perforation discharge model, the fracture initiation and the fracture dynamic extension model. Furthermore, we analyzed the wellbore pressure changes and the fractures propagation under single and combined propellants at different ratios. The calculated results demonstrated that fast deflagration fracturing could be initiated using combinations of the first-phase propellants with different burning rates and the multi-directional wellbore pressure was reached at once; a longer burning time of the propellant might be held to maintain the high pressure for the full extension of the fracture, using the second-and the third-phase propellants; when the amount of the first-phase propellants and the total amount of the propellants were determined, the deflagration loading rate and the multi-directional fracture initiation pressure tended to decrease slightly as the lowest burning rate of the third-phrase propellant's proportion rose up, though not obviously; the eventual extension lengths of the fracture in different directions were, however, very sensitive to the proportion of the second-and third-phase propellants. These results improved our understanding of the coupling mechanism of the combined pulse fracturing, and might be used to optimize the mass ratio of propellants.