Assessing the mechanical microstructure of shale by nanoindentation : the link between mineral composition and mechanical properties

摘要

Shale is a multi-phase, multi-scale sedimentary rock that makes up 75% of the earth's sedimentary basins and is especially critical in petroleum engineering applications. At macroscopic scales, shales possess a diverse set of possible compositions, resulting in a diverse set of mechanical properties. This thesis assesses microstructure and material invariant properties of shale as the link between engineering performance and composition. A comprehensive experimental microporomechanics approach, employing advanced experimental and analytical nanoindentation techniques, provides the basis for assessment of microstructure and material invariant properties. Nanoindentation experiments and analysis tools are designed to probe and infer the elastic and strength properties of the porous clay composite in shale. The results of this investigation show that properties of the porous clay composite scale with the clay packing density in the material, but otherwise do not depend on mineral composition. These scaling relationships are representative of a granular composite of spherical particles, and lead to identification of intrinsically anisotropic material invariant elastic properties and intrinsically isotropic material invariant hardness properties. The material invariant hardness represents a combination of cohesive and frictional behavior that is seen to scale with the average clay packing density in the sample. Nanoindentation results also provide evidence of packing density distributions that are analogous to pore size distributions.