Estimating Anisotropic Brittleness of Shale Based On a New Rock Physics Model

It is widely known that shale often shows high anisotropic property. Ignoring shale anisotropy can induce errors in brittleness estimation. However, in oil industry, the common way to evaluate the brittleness of shale is based on using isotropic parameter (i.e. Young’s moduli and Poisson’s ratios), since it can be easily calculated based on measured elastic wave velocity from geophysical data. Anisotropic shale rock physics modeling offer us a new way to estimate the brittleness of shale from anisotropic aspect. Our studies firstly introduce a new rock physic model for shale. Based on our anisotropic shale model. The relationship between physical properties (like pore geometry, TOC, shale lamination and dip angle of shale formation) and elastic parameters (like anisotropic YM and PR) are established. Our modeling results coincide with the real data points of shale. The prediction shows the vertical/horizontal YM always below 1 while the vertical/horizontal PR can be either over or below 1. We find different extent of shale lamination may be the reason to explain the random distribution of Vani. And the brittleness of shale can vary significantly while drilling due to the strong anisotropy of shale formation.