Q Inversion and Comparison of Influential Factors among Three Methods: CFS, SR, and AA

The goals of this study were to examine factors influencing Q inversion and to provide references for practical application.Three different methods for inverting Q values with VSP data were explored,including centroid frequency shift(CFS),spectral ratio(SR),and amplitude attenuation(AA).Comparison between the CFS and the other two methods was conducted on frequency band widths and low attenuation,wavefield components,interface interference,and thin layers.Results from several sets of VSP modeling data indicated that the CFS method is more stable and accurate for dealing with thin and high Q layers.Frequency band width,especially the presence of high frequencies,influences the inversion effect of all three methods.The wider the band,the better the results.Q inversion from downgoing wavefield was very similar to that of the upgoing wavefield.The CFS method had fewer outliers or skip values from the full wavefield than the other two methods.Moreover,the applications to Q inversion for the set of field VSP data demonstrated that the Q curves from the CFS method coincided with the geological interpretations better than the Q curves of the other methods.Meanwhile,inverse Q filtering shifted the frequency component from 25 Hz to 35 Hz.The results demonstrated that the Q curve is more sensitive to geological horizons than velocity.

A Modified Multiple Matching Method Based on Equipoise Pseudomulti-Channel Filter and Huber Nor

This study is aimed at improving multiple adaptive subtraction.We propose a modified pseudomulti-channel matching method based on the Huber norm,to adjust the matching differences on frequency and phase between the predicted multi-ples and original data.The second-order derivative of the predicted multiples is utilized to replace the derivative of its Hilbert transform.Due to the additional frequency term,this method can enhance the high-frequency component.We introduce 180◦phase rotation of the multiple channels,which can decrease phase differences.The Huber norm interpolates between smooth L2 norm treatment of small residuals and robust L1 norm treatment of large residuals.This method can eliminate the restriction of large value conditions from the L2 norm and weaken the condition of orthogonality from the L1 norm.The applications of the Pluto and Delft models shows that compared with pseudomulti-channel matching filter,the main frequency is increased from 36 Hz to 38 Hz,and the primary reflection wave is more concentrated.The practical application of field data verifies the effectiveness of the proposed method.