| Fluid transport and mechanical properties of fluid-saturated illite-rich shale from the Wilcox Formation have been investigated. Effective pressure laws have been determined for permeability and for deformation, and effects of fluid compositions determined using, 1M solutions of NaCl, KCl, and CaCl 2 as well as with distilled H2O. Permeabilities exhibit significant anisotropy at relatively low effective pressure Pe with fast transport parallel to bedding and slow transport perpendicular to bedding. With increasing Pe, permeabilities measured parallel to bedding decrease more rapidly than those measured perpendicular to bedding, reaching nearly isotropic values of ∼ 10--21 m2 at Pe > 10 MPa. Permeabilities are affected significantly by changes in fluid composition, consistent with exchange of divalent cations for monovalent cations at clay mineral surfaces. Permeabilities exhibit significant nonrecoverable behavior upon cyclic loading and changing composition of incoming pore fluids. Critical state theory describes the path dependence of permeability change with P e in the laboratory time scale. Diffuse double-layer theory of clay surfaces offers an explanation for changes in permeability with changes in fluid composition.; The failure strength of Wilcox shale increases with increasing effective pressure. Triaxial deformation experiments performed over six orders of magnitude in strain rate span time scales that represent drained and effectively undrained conditions. However, failure strengths exhibit consistent rate hardening, according to 3&d2;=AT,P eexpw s1-s3 . Despite time scales that do not allow pore fluid drainage, pore pressures at failure may not be large. Pore pressures of undrained Wilcox shale samples subjected to changing confining pressure follow confining pressure closely, with a Skempton parameter B ≅ 1. However, pore pressure generation due to differential stress is comparatively small, and volume reductions early in triaxial compression experiments are nearly compensated by late-stage dilatancy near failure. Failure strength of Wilcox shale is remarkably insensitive to fluid composition in contrast to observed effects of clay hydration on strength and effects of fluid composition on permeability. |
