Synthetic waveforms of the acoustic field in cased boreholes and their time-frequency distribution

Synthetic acoustic pressure waveforms of the acoustic field excited by a point source in cased boreholes are calculated. All three kinds of lithology in field and various cement bonding cases for the two interfaces outside the steel casing are considered. The center frequency of acoustic source used in calculation is the same with the logging tools used in field. The time-frequency analysis based on Wigner-Ville distribution is used to synthetic waveforms. The obvious varied regularities of the casing arrivals and the pseudo-Rayleigh waves can be observed in waveforms and time-frequency distribution when the bonding conditions of the two interfaces change. The time-frequency distribution changes along with the changing of the thickness of cement layer when the cement and formation is not bonded. These characteristics and the characteristic of formation body waves can be used as an important basis for the evaluation of cement bonding quality outside the steel casing. The formation body waves in the formation with medium velocity have the biggest energy among the all three kinds of lithology, it's advantageous to the evaluation of cement bonded quality.