The Effect of Saturation on Shear Wave Anisotropy in a Transversely Isotropic Medium

摘要

Experimental and theoretical studies were performed to investigate the effect of saturation on compressional and shear wave anisotropy in a transversely isotropic medium. Experiments were performed on samples of Austin Chalk, a carbonate rock with fabric-controlled layering. Samples were saturated with either water or silicone oil. Two theoretical approaches were used: a low frequency limit, LF, calculation based on Backus Averaging for layered media and a high frequency limit, HF, based on time averaging. Neither model provides a complete description of the data. The LF model predicts compressional wave velocity better than the HF model. However, for Sv wave and Sh wave, HF model exhibited a better fit to the data at incident angles smaller than 30 degrees, while the LF Model provides better fits for incident angles greater than 70 degrees. Modeling the sample as an effective medium (LF) captured most of the phenomenon observed in the experimental data such as a reduction in compressional wave anisotropy upon saturation and that the modulus measured by a shear wave propagated parallel to layers increased with increasing fluid viscosity. Both the HF time-averaging approach and the LF Backus averaging approach yielded similar general trends, but neither method captures the complexity of carbonate rock.