oa Relationships among Porosity, Permeability and Seismic Velocity of Shales

This study focuses on relationships among porosity, permeability and seismic velocity of shales. A total of thirty well characterized, brine-saturated (35000 ppm NaCl) synthetic shale of varying textural and mineralogical compositions were compacted mechanically both in triaxial and oedometer cells under controlled pore pressure and proper drained conditions. Results show that kaolinite dominated shales compact more but have higher permeability and seismic velocity compared to smectite dominated shales at same stress/depth. Permeability differs a maximum five orders of magnitude at the same porosity for different shales. For velocity-permeability relationship between kaolinite- and smectite-dominated shales, a maximum four orders of magnitude are observed. Velocity/porosity can therefore not be good proxy to estimate reliable permeability in shales. Comparison of experimental and published data show a good agreement and illustrated that a better understanding of mineralogical and textural relationships can be significantly improved to establish relationships among porosity, permeability and seismic velocity of shales. In addition to the existing database, the new experimental data (this study) can improve the calibration of fluid flow modeling, seismic and well-log interpretation and evolution of shale rock properties. The experimental results may also be of importance for structural design, slope stability analysis and waste disposal efforts.