Dynamic and static moduli

Static and dynamic bulk moduli (K s and K d ) are measured as continuous functions of pressure from zero to 2‐3 kilobars for two sandstones, a tuff, limestone, granite, and oil shale. Results for the sandstones and granite are in good agreement with previously reported data with K s /K d varying from about 0.5 at atmospheric pressure to close to unity at pressures 2 kilobars and above. For rocks behaving elastically under static loading, the K s /K d ratio is inversely related to the microcrack density. For the limestone, time dependent deformation associated with pore collapse results in K s /K d ratios approaching 0.1 at high pressure. Upon unloading, while initially high ( ∼ 1.0) at high pressures, K s /K d becomes lower than values obtained during loading at low pressures ( < 1 kilobar) due to opening of microcracks generated during pore collapse. For the oil shale, in which few microcracks exist, K s /K d remains relatively constant with pressure at a value of about 0.7.