Modeling of Compaction Trends of Anisotropic Elastic Properties of Shales

摘要

Modeling of anisotropic elastic moduli of shales is a long-standing problem in rock physics. Every year, industry and academia conduct hundreds of measurements of elastic and geomechanical properties of shales complemented with detailed mineralogical analysis, electron microscopy, and microtomographic images. However, a predictive theoretical model, which would be able to predict elastic properties of shale based on its detailed characterization, is still lacking. This is due to the complex multicomponent nature of shales which leads to multiparametric character of the modeling. It is extremely challenging to separate and investigate effects of these multiple parameters individually on natural shale samples. In this work, we analyze a unique data set of elastic properties measured on two artificial shales compacted with carefully controlled mineralogy, microstructure, and porosity. We developed a new modeling approach that consists of four steps that take into account effects of (1) the orientation of clay particles, (2) porosity, (3) silt fraction, and (4) the stiffness of contacts between clay particles. Three of these four steps require only measurable parameters and, only at the final step, the effect of unknown parameters (namely, contact properties of clay platelets) are accounted for. Further, the obtained contact properties are shown to be in a good agreement with the contact properties estimated for natural shale samples. Finally, we demonstrate the effect of each of these identified parameters on elastic coefficients and Thomsen's anisotropic parameters.