| The petrographic and physical characterizations of Boise sandstone are presented and the results of special triaxial testing along predetermined stress or strain paths are summarized.;For simulating oil wells under constant outer pressure and increasing inner pressure, a numerical solution to an axisymmetric problem with plane strain has been obtained. The analysis developed in this case is also valid for other compressible, strain-hardening reservoir rocks with alternative nonlinear yield functions.;A simplified model, which links the maximum shear stress, mean stress and plastic volume strain with a linear relation, is applied to seek an analytical solution to the same problem as in the numerical case. This solution facilitates locating the elastic-plastic interface and judging the maximum allowable internal hydraulic pressure for a well in reservoir strata.;With the relations among stress, strain and porosity revealed by experimental data, a plasticity model is constructed and named CAL Rock model to provide a practical constitutive law for solving boundary value problems. This model is of the critical state type and the critical state line, for triaxial states, consists of an initial brittle failure section, a Tresca constant shear stress section and a Mohr-Coulomb frictional section. Parabolic yield surfaces are given for both isotropic and kinematic hardening cases. |
