Numerical simulation on fracture propagation of methane in-situ explosion fracturing in shale gas reservoirs

Key words:  shale gas reservoirs  explosive fracturing  continuum-discontinuum element method  numerical simulation  natural fracture  fracture propagation

Abstract:

Fracturing viamethane explosion is proposed as a novel reservoir reconstruction method, in which in-situ resolved methane gas is used as explosion source for fracturing of shale gas reservoirs. In this study, based on the continuum-discontinuum element method (CDEM), a numerical simulation model of methane explosion fracturing was established by combining the Landau explosion source model and the linear elastic tensile-shear composite fracture constitutive model. The numerical simulations of the methane explosion fracturing in vertical wells for shale gas reservoirs were carried out. The effects of peak pressure, pressurization rate, initial minimum principal stress, initial stress difference and natural fractures on explosion fracture propagation were analyzed.The results show that methane explosion fracturing can generate complex fractures around the wellbore, and with the increase of peak pressure and pressurization rate, as well as the decrease of initial minimum principal stress, the propagation range of the explosion cracks can be increased, in which the peak pressure is the most significant factor. The fracture range in the direction of the maximum principal stress is larger due to the influence of stress difference, and larger stress difference can lead to a more obvious deviation of fracture range. The existence of natural fractures (NFs) can enhance the effect of explosion fracturing. A greater NFs density, a longer fracture length, and a smaller angle between the dip angle of NFs and the σh direction can increase the range and area of the explosion fractures.