Abstract

Dispersion analysis of flexural waves in dipole sonic log can reveal the anisotropy, shear velocity, and presence of fractures within the formations adjacent to the borehole. In this study, we implement the Phase Shift method to compute the dispersion of dipole sonic log over the Bakken and its adjacent formations. We found significant differences in the shear velocities of the shale members (the Upper and Lower Bakken) versus the non-shale members (the Lodgepole, Middle Bakken, and Three Forks). We therefore, conclude that dispersion characteristics can be used for lithology identification. We also found that the existing method to analyze dispersion images based on the assumption of HTI medium with a single set of fractures is insufficient for characterizing the anisotropy of more complex fractured media