A new acoustic remote sensing method utilizing borehole low-frequency dipole shear wave

Acoustic remote sensing technology utilizes a borehole acoustic wave to radiate and receive elastic waves to and from a near-borehole geological structure or abnormity body.This paper aims to break through current limitations of single-well reflection imaging logging,proposes a new acoustic remote acoustic sensing method,i.e.,the cut-off frequency phenomenon of the borehole flexural wave is used to emit acoustic wave of a borehole dipole source exciting below the cut-off frequency.Through the comparison and analysis of the radiation field inside and outside the borehole excited by a borehole dipole source above and below the cut-off frequency,we has pinpointed the far-field radiation characteristics and advantages of dipole shear wave below cut-off frequency excitation.Combined with numerical simulation,the paper analyzes further the reflected wave field above and below the cut-off frequency.These analysis results show that this method can avoid the saturation effect in the quantitative data because of the airy phase great amplitude,and it is more advantageous compared to the traditional measurement mode.Reflection wave amplitude is strong for near-offset and decreases when receiver offset increases and we do not need long offset tools for the imaging application.