Brittleness and Fracture Detection Using Data-driven Optimal AVAZ Inversion

Amplitude Variation with Angle and Azimuth (AVAZ) inversion is an effective tool for estimating brittleness and fracture properties of shale gas reservoirs. However, traditional AVAZ inversion often relies on a linearized AVAZ approximation, which may not be suitable for cases involving strong contrasts in rock properties or long-offset data. Additionally, the large number of model parameters present significant challenges for multi-parameter simultaneous inversion. To address these issues, we propose a novel data-driven optimal AVAZ inversion method to estimate the brittleness indicator and fracture density in horizontal transversely isotropic (HTI) media. Initially, we use the exact anisotropic Zoeppritz equation and convolution model to generate reference AVAZ gathers based on well-log data. The singular value decomposition (SVD) technique is then applied to obtain optimal basis functions and coefficients, which directly link band-limited elastic and fracture reflectivities to the observed AVAZ data. Finally, we employ post-stack inversion to invert these band-limited reflectivities for elastic and fracture parameters individually. The effectiveness of our method is demonstrated using a synthetic example and field data. Our results reveal that it provides more accurate estimates of brittleness and fracture density than traditional AVAZ inversion, offering significant improvements in seismic characterization of rock brittleness and natural fractures.