Microscale approximation of the elastic mechanical properties of randomly oriented rock cuttings

Abstract

This study examined a method for approximating the transversely isotropic (TI) elastic mechanical properties and bedding plane orientations of randomly oriented rock cuttings. Microindentation testing was conducted on multiple rock cuttings with unknown bedding orientations to obtain their experimental indentation moduli. The measured indentation moduli were assumed to be functions of both the bedding orientations and the intrinsic TI mechanical properties of the rock cuttings. This assumption holds due to the anisotropic stress history and preferred horizontal alignment of the rock fabric along the bedding direction, as well as the presence of plate-like clay particles with intrinsic TI mechanical properties. An anisotropic contact mechanics solution was then utilized to predict both the TI elastic mechanical properties and bedding plane orientations of the cuttings using a constrained inverse algorithm that minimizes the error between the predicted indentation modulus (a function of both the predicted elastic constants and the orientation of the cuttings) and the experimental indentation modulus. Several constraints were imposed on the inverse algorithm to mathematically bound the TI stiffness matrix and optimization results. A Monte Carlo simulation was also incorporated into the inverse algorithm to consider the effects of uncertainties in the experimental results. The results obtained from the proposed indentation–inverse algorithm approach show good agreement with the results obtained using non-invasive ultrasonic pulse velocity measurements on a 2.5 cm cube sample.