Orthorhombic AVAZ inversion in the Laplace-Fourier domain

Abstract

A homogeneous isotropic background rock permeated by two sets of invariant horizontal and vertical aligned fractures is equivalent to a long-wavelength effective orthorhombic medium. Amplitude variation with angle and azimuth inversion (AVAZ) inversion has emerged as a fundamental and important tool for estimating elastic and anisotropic parameters. However, the low-frequency information of real seismic data is often missing or highly contaminated by noises, making it a great challenge to derive a broadband inversion result that conforms to geology. Here, we proposed a two-step orthorhombic AVAZ inversion to estimate model parameters (P-wave velocity, S-wave velocity, density, horizontal and vertical fracture densities) from azimuthal seismic data, which includes (1) Laplace-Fourier domain inversion for estimating the low-frequency components of model parameters, and (2) frequency-domain inversion for estimating the complete inversion results of model parameters. We demonstrate our approach by showing inversion examples of both the synthetic data and real seismic data acquired over a fractured shale gas reservoir in the southern Sichuan Basin. Note: This paper was accepted into the Technical Program but was not presented at IMAGE 2022 in Houston, Texas.