SH wavefield simulation of dipole acoustic reflection survey for multi-fracture system

ABSTRACT Numerical simulation of borehole acoustic reflection imaging of far-borehole fractures requires consideration of the borehole size and the fine structure of the fractures. The 3D discretization for fine structure modeling results in a huge number of grid nodes and extremely long computational time, which severely limits the efficiency of forward modeling of far-borehole reflection wave fields in fractured reservoirs. To address this problem, an analytical method was proposed for quickly calculating snapshots of acoustic reflection imaging wave fields on both sides of a fracture using the far-field asymptotic solution of dipole radiation shear wave displacement. This method combines the angular spectrum method with the slip interface theory. The waveforms obtained are consistent with those obtained by 3D finite-difference time-domain elastic wave simulations. For the same fracture model, the computational efficiency of the analytical method is two orders of magnitude faster than that of the finite-difference numerical method. Using this method, the effect of shear stiffness changes on the real-time propagation of dipole SH wave fields in a double-fracture system was analyzed. These findings can be used to characterize and interpret multi-fracture systems in single-well reflection imaging using field data. The results show that shear stiffness changes caused by near-fracture filling materials are a prerequisite for the effective identification of far-fractures in multi-fracture systems. The analysis results provide a theoretical basis for time domain simulation and imaging analysis of dipole acoustic reflection imaging wave fields in multi-fracture systems.