Modeling the anisotropic elastic property of the Eagle Ford Shale with complex micro-scale fabric

Abstract

The purpose of this work is to model the anisotropic elastic properties of the upper Eagle Ford Shale by accounting for the micro-scale fabric. The micro-scale fabric significantly influences the elastic properties and anisotropy of the rock. In the shale, the complex micro-scale fabric comes from the platy clay minerals, non-spherically shaped kerogen, and their preferred orientation patterns. The method presented in this work include three steps: anisotropic DEM modeling to construct an effective VTI medium; an orientation correction to account for the orientation patterns of clay minerals; and a pressure correction to account for the different pressure-dependent behaviors between Pand Swaves. This work shows that the stiffness decreases with clay volume, kerogen volume and porosity. The anisotropy increases with porosity and kerogen volume, but the influence of clay volume on anisotropy is more complex. Specifically, the anisotropy increases with clay volume at relatively low clay concentrations; however, the anisotropy is nearly constant, or even slightly decreases, as clay content continues to increase. This result suggests that the preferred orientations of clay clusters are preserved at relatively low clay concentrations at the core scale, but they vanish at high clay concentration at the same scale in the Upper Eagle Ford Shale.