Azimuthal AVO over a simulated fractured medium: A physical modeling experiment

Abstract

A seismic physical model experiment has been conducted to acquire multi-offset multi-azimuth P-wave 3D seismic data, and to verify the suitability of physically-modeled data for AVAZ (amplitude variation with azimuth) analysis. Our model consisted of an azimuthally anisotropic layer, phenolic layer simulating a vertically fractured medium, overlain by two isotropic layers with the top most layer being water. The amplitudes reflected from the top of the fractured layer have been picked from the primary reflection; acquisition was designed to avoid the overlapping of the primary and ghost events. The picked reflection amplitudes required corrections to make them suitable for an AVAZ study. In addition to amplitude corrections used for seismic field data, a directivity correction specific to the physical model transducers was needed. The corrected amplitudes from different azimuths showed a clear azimuthal variation caused by the fractured layer, and agreed with amplitudes predicted theoretically.

Fracture clustering effect on amplitude variation with offset and azimuth analyses

“…We assume that fractures are vertical and parallel to each other in the simulations because subsurface natural fracture planes tend to be vertical and parallel to the maximum horizontal stress direction (Zoback, 2010). Previous numerical and experimental studies (Tadepalli et al, 1995;Fatkhan et al, 2001;Alhussain et al, 2007;Chichinina et al, 2009;Mahmoudian et al, 2012;Far et al, 2014) on models with regularly spaced fractures have demonstrated that the EMM and DFM models are equivalent when fracture spacing is sufficiently small compared with the wavelength (e.g., < λ∕10), which is the foundation for the use of EMM in fracture characterization. However, fractures are unlikely to be uniformly distributed in the earth.…”

Characterizing the degree of amplitude‐variation‐with‐offset nonlinearity in seismic physical modelling reflection data

“…Its maximum amplitudes were picked using a method for avoiding ghost interference described by Mahmoudian et al. ().…”

“…We follow a processing flow designed to correct the amplitudes picked below several elastic and/or acoustic interfaces (Mahmoudian et al. ). Geometrical spreading .…”

“…We nevertheless adopted the more complicated processing flow because it has been rigorously validated (Mahmoudian et al. ). Emergence angle . The traced P‐P raypath is also used to determine the emergence angle at the receiver location, and by doing so, the recording is converted to the total motion.…”

“…The Consortium for Research in Elastic Wave Exploration Seismology (CREWES) physical modeling facility at the University of Calgary (e.g., Wong et al 2009;Cooper, Lawton, and Margrave 2010), was used to generate data sets from which AVO and amplitude-variation-with-azimuth (AVAZ) responses of anisotropic targets can be examined (Mahmoudian, Wong, and Margrave 2012). To facilitate the analysis, a pre-processing procedure was developed to transform recorded amplitudes into approximations of reflection coefficients.…”