Relating Static and Dynamic Mechanical Anisotropies of Shale
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Experimental studies of shale cores of different orientations have been performed to compare the angular dependence of dynamic moduli acquired at ultrasonic frequencies with static moduli (Young’s moduli and Poisson ratios) obtained during initial loading and during subsequent unload – reload cycles. The data show that the dynamic moduli by far exceed their static counterparts. Dispersion explains part of this behavior: Dynamic moduli measured at seismic (10 Hz) frequency are significantly smaller than ultrasonic moduli, but reasonably similar to stiffnesses obtained from finite stress cycles. The difference between moduli obtained during initial loading and during stress cycles is largely caused by non-elastic behavior.