A new method of extracting shear slowness from borehole mode waves

Asymmetrical sources were introduced into modern well logging tools for measuring shear slowness of soft formation. However, the mode waves exciting in borehole are all dispersive waves. It is impossible to right extract the shear slowness using traditional slowness time coherence (STC) method. A new shear slowness extracting method is proposed based on phase spectrum coherence in this paper. The method in verified by both the synthesized flexural waves and field data. The results show that the proposed method is stable and reliable.