Modeling the effects of pore aspect ratio, porosity, and seismic anisotropy on wave velocity dispersion and attenuation patterns in oil- and brine-saturated carbonates using a dynamic self-consistent anisotropic approach

Abstract

In this work, numerical modeling was performed using a dynamic self-consistent (SC) anisotropic micromechanics approach. This study examines how porosity, pore aspect ratio, and seismic anisotropy affect the velocity dispersion and attenuation patterns of P-waves and polarized S-waves (SH and SV) traveling through oil- and brine-saturated carbonate rocks (3D body) at seismic, sonic, and ultrasonic frequencies. Here, the carbonate rock was idealized as a mineral carbonate matrix embedded with aligned ellipsoidal fluid inclusions of aspect ratio \(\gamma\). These ellipsoidal inclusions represent the porosity \(\phi\), which is saturated with fluid. The studied rock was assumed to have a vertical axis of symmetry that is perpendicular to the plane of alignment and therefore will show vertical transverse isotropy (VTI). Wave velocities were modeled considering a variety of porosities (\(\phi =\)5, 10, 15, and 20%), aspect ratios (ranging from \(\gamma = 0.2\) to \(\gamma = 5\)), and angles of incidence (\(\theta = 0^\circ ,\) \(30^\circ ,\)\(45^\circ\), \(60^\circ\), and \(90^\circ\)), where \(\theta\) is the angle between the symmetry axis and the direction of wave propagation through the rock. Overall, results showed that the largest changes in P- and SH-wave velocities are due to variations in \(\phi\) (up to 15%), followed by changes in \(\theta\) (up to 6%), and then by changes in \(\gamma\) (up to 4.3%). By contrast, for SV-wave velocities the order changes in the last two parameters. Finally, the variations in P- and S-wave velocity dispersion and their maximum attenuation are greater for oblate ellipsoids \(\left(\gamma <1\right)\) than for prolate ellipsoids\(\left(\gamma >1\right)\), regardless of porosity, angle of incidence, and aspect ratio.