Seismic Fracture Characterization by QVOA Analysis Using Simulated Seismic Data by Physical Modeling

Abstract

Vertical fractures cause azimuthal anisotropy in the wave-energy attenuation. To predict the fractures’ azimuth from seismic data, we develop a method of analysis of azimuthal variations in the attenuation. It is so-called QVOA analysis that means “Q Versus Offset and Azimuth”. Fractures’ network can be represented as an anisotropy model of a transversally isotropic medium with a horizontal axis of symmetry (HTI). As a sought-for parameter, we consider the fractures’ azimuth (φ₀), which identifies the fracture strike. We develop our QVOA method to estimate the φ₀-azimuth of fractures from seismic data simulated by physical modeling. The Q-data on the attenuation are estimated along three seismic lines with 3 azimuths of the source-receiver line, φ = $0^\circ$, φ = $45^\circ$, and φ = $90^\circ$. To estimate the fracture-strike φ₀-azimuth, we use the least squares method (LSM), namely, we minimize the functional of the difference between the theoretical function Q⁻¹(θ, φ–φ₀) and the real attenuation estimated from seismic data. We estimate the azimuth of the fracture strike (φ₀) using our new Canonical equation of the Q⁻¹(θ, φ–φ₀)- function. The Canonical formula results in the smallest and the most stable absolute ∆φ₀-angle error of $0.26^\circ$ (compared to the older versions of QVOA-method). The maximal attenuation is obtained at the φ = $0^\circ$the orthogonal direction to the fracture strike; and the minimal attenuation is at the φ₀ = $90^\circ$, which is the fracture-strike azimuth. Thus, the experiment fully confirms the theory.