XU Song, TANG Xiaoming, et. al.
Semismic Shear Wave Anisotropy in Cracked Rocks and an Application to Hydraulic Fracturing
Geophysical Research Letters, ISSN: 0094-8276
https://doi.org/10.1029/2018GL077931
Abstract: Subsurface rocks often contain cracks/fractures with various orientations: aligned, conjugated, and randomly oriented, giving rise to different types of seismic anisotropy. We develop an effective approach for the elastic wave-scattering theory to accurately calculate anisotropic properties in the presence of single and/or multiple fracture sets. Two specific models, the equivalent aligned crack system and the equivalent orthogonal crack system, are considered for the calculations. The equivalent aligned crack system generates significant anisotropy, while the equivalent orthogonal crack system exhibits weak anisotropy due to the interaction of cracks with different orientations. The theory is applied to interpret acoustic anisotropy measurements acquired in hydraulically fractured formations, where theoretical predictions and measurements are in good agreement.
Plain Language Summary Cracks/fractures in rocks and their alignment directions can strongly affect the elastic wave velocities and anisotropy. The effective elastic-wave scattering theory of this study can accurately compute the anisotropy elastic properties in the presence of single and/or multiple fracture sets. Particularly useful is the ability to handle multiple crack sets, which allows for analyzing the effect of conjugated fractures encountered in real rocks. The results can be used to provide an effective method for interpreting elastic-wave anisotropy data from seismic (e.g., borehole acoustic) measurements.
