Numerical Homogenization of Anisotropic Static Elastic Properties of Soft Mudrocks

Soft mudrocks have low permeability and are mostly treated as sealing geological formations. Clay-rich soft mudrocks are also classified as the transversely isotropic (TI) material due to the intrinsic preferred fabric orientation. The TI elastic properties of soft mudrocks are highly dependent on the containing mineralogical compositions and clay fractions. Thus numerical modeling is necessary to estimate the behavior of soft mudrocks. In this study, a two-dimensional homogenization model is employed to assess the elastic moduli of soft mudrocks. Clay-water composites are treated as the hosting matrix, and non-clay minerals are placed in the REV as the inclusions. The inclusions are placed randomly in different sizes. In order to consider the partial flexibility between the non-clay minerals and clay-water composites, an imperfect boundary is defined between the inclusions and matrix using the eXtended Finite Element Method (XFEM). The periodic boundary condition is imposed on the REV, and the homogenized anisotropic elastic moduli of rocks with different clay fractions are estimated. The numerical results were validated using published experimental data on the static TI elastic properties of soft Colorado shale samples. The results show the predictable decreasing trends in elastic modulus of soft mudrocks with increasing of the clay fraction.