Phase velocity approach for Suspension P–S Logging data analysis

Abstract

Due to the short receiver interval, results of Suspension P–S Logging are sensitive to the picking of first arrivals, which is currently carried out by manual picking in the time domain. However, manual picking can be ambiguous and depends heavily on the data quality and analysts' experiences. Furthermore, no information regarding the effective frequency is obtained from first arrival times. A data reduction method based on phase velocity analysis of borehole acoustic waves is proposed herein. The aim is to provide an automatic procedure for more objective velocity analysis. The procedure utilizes the two-channel dispersion curve analysis, but becomes semi-empirical because an additional assumption is made to simplify the calculation and avoid the phase un-wrapping problem associated with the lack of low-frequency information. Some field data were used to evaluate the empirical parameter for calculating the shear wave velocity. Results show that the velocity difference between the proposed method and the conventional method based on manually-picked first arrivals is mostly within 15%. The proposed method can be automated and provide the effective frequency of the obtained shear wave velocity.