Microseimic forward modeling and full-waveform inversion of focal mechanisms for viscoelastic vertically transverse isotropic media

The microseismic moment tensor can describe the details of rock failure in reservoirs, which helps reveal geomechanical characteristics of hydraulic fracturing reservoirs. Moment tensor inversion of focal mechanism is important to development of unconventional oil and gas. Hydraulic fracturing is usually conducted in shale oil and gas reservoirs. The media near the source typically have anisotropic velocity and anisotropic attenuation. So it is necessary to study microseismic signal propagation in anisotropic attenuative media. Based on microseismic records, the moment tensor can be calculated through waveform inversion. While ignoring the velocity anisotropy and attenuation of the source area will lead to errors in the focal mechanism inversion. To solve this problem, we propose a full-waveform inversion method for focal mechanism considering anisotropic attenuation. The vectorized Graphics Processing Unit (GPU) parallel pseudospectral method is used to simulate synthetic seismic records in viscoelastic Vertically Transverse Isotropic (VTI) media. Through the full-waveform inversion to match the synthetic waveforms and received waveforms, the focal mechanism moment tensor can be obtained by the optimization algorithm. Numerical simulation tests verify the effectiveness of this method. We further analyze the influences of anisotropic velocity, anisotropic attenuation, noise and observation system on the microseismic focal mechanism inversion results. Research suggests that considering the attenuation anisotropy is important for reliable inversion of focal mechanism.