Research On Inversion And Application Of Shear-wave Radial Profile Of Formation Around Well

Shear-wave slowness around the well is of great importance in evaluating the stability of the borehole and judging the fluid invasion and selecting the perforation position.Dipole shear wave logging which has low excitation frequency and deep detection depth is an effective method to determine the radial profile of shear wave slowness around the well.There are two methods to invert the profile of dipole S-wave.One is the inversion algorithm which combines the perturbation method and BG theory.Another method is the high-frequency constrained inversion method based on parameter.Two methods are based on the influence of the change of radial slowness outside the well on the dispersion characteristics of the dipole shear wave,but both methods do not consider the influence about the instrument,so they are not accurate enough in the application of actual data processing.This paper refer to a theory of equivalent instrument,studies the inversion method of S-wave slowness profile without the influence of the instrument.The different acoustic logging instrument is equivalent to an elastic rod with only two parameters.Using these two parameters to modify the dispersion equation of dipole shear wave to simulate the influence of the instrument on the dispersion curve.The modified dispersion equation is substituted into the objective function of the two inversion methods.Studying the influence of instruments on inversion results to improve the accuracy of inversion,processing the actual logging data,and the results verify the validity of this theory.