Laboratory measurements of brittleness anisotropy in synthetic shale with different cementation

Abstract

Hydraulic fracturing is required for economic production of hydrocarbons from low-permeability reservoirs such as gas shales. Brittleness is now recognized as one of the most important parameters to evaluate the effect of hydraulic fracturing. Shales are usually anisotropic, and as a result, the brittleness of shale is also anisotropic, which changes with the angle between the propagating direction and the axis of symmetry. In this study, we investigate the effect of cementation on the brittleness of a set of synthetic shale samples. We mixed fine particles (≥3000mesh), brittle mineral, clay, carbonate, organic carbon and cement powder together in different amounts and then cold-pressed the mixture to obtain solid synthetic samples. Laboratory measurements of density, P-wave and S-wave velocities in 0°,45°and 90° directions were performed on the samples to calculate elastic stiffness tensor C. By using transition matrixes T & T', we transformed stress σ and strain ε, between global and local coordinates, and finally obtained the information on brittleness anisotropy of shales.