| The subject of texture mediated rock rheology and failure is quite new to the science of geologic materials. The resolution of this problem is fundamental to the analysis of various rock deformation problems encountered in the petroleum, mining and materials industries. Finding links between rock failure properties, texture and composition is necessary for the understanding of subsidence histories and the development of fault systems in sedimentary basins; improving geophysical methods for measuring rock strength; and rigorously analyzing problems associated with wellbore stability, sand production and hydraulic fracture containment.; The first part of this research involves the development of new empirical formulae, which relate the failure properties of clastic and carbonate rocks to their texture and composition. The failure criterion used in this study is based on the Drucker-Prager model, which accounts for the effect of all principal stresses. The model's material parameters are fitted as functions of porosity, grain size and composition. Results show that increasing porosity reduces rock strength and enhances rock ductile behavior. The rock compressive strength appears to be less sensitive to grain size than porosity and composition for both carbonates and clastics.; The second part of this work is concerned with the development of a unified rheological model for rock deformation. The model avoids the need to solve detailed mechanical aspects of a stressed medium by using macroscopic theories such as plasticity or viscoplasticity. Instead it is based on the assertion that strong coupling exists between the state of stress, texture, rock failure and mechanical properties. As the rock system deforms, its texture, including porosity, and grain size, shape and packing changes. This results in a change in the failure and mechanical properties of the material, which causes a change in the state of stress, which in return leads to a further change in texture. By simultaneously solving the fully coupled system of equations governing rock texture, state of stress and failure properties, we can calculate the distribution in space and evolution in time of rock deformation.; The third part of this research provides a theoretical model for vug collapse in a porous medium. The model is based on mean field theory that maps onto the matrix-inclusion problem of Eshelby (1957), combined with Drucker-Prager failure criterion (1951). The model is used to estimate the conditions of failure of the medium surrounding the vug of an arbitrary rock subject to an arbitrary type of loading. |
