抄録
In the present paper, application and limitation of integral method of seismic data for recovery of acoustic impedance is described.
After an approximate integral formula for acoustic impedance is derived, the limitations of its formula on the following items are investigated.
1. Effect of additive noise in seismograms.
2. Increase in error with time caused by noise in the estimated acoustic impedance.
3. Problem on recovery of acoustic impedance from band-limited seismic data.
4. Broadening of frequency contents of seismic data by wavelet processing.
5. Requirement for addition of low-frequency contents to acoustic impedance.
As a result, the following conclusions are obtained.
1. When the reflection coefficients are known and noise free, the natural logarithm of the acoustic impedance of each layer is approximated by addition of the twice of integral of the reflection coefficients to the logarithm of the acoustic impedance of the first layer.
2. The approximate integral method of amplitude in seismograms is sensitive to noise. The accuracy of recovery of acoustic impedance decreases against arrival time because the noise is accumulated.
3. When the reflection coefficients are band-limited, the acoustic impedance is not accurately reconstructed by the integral method. Especially, a lack of low-frequency contents affects seriously the accuracy of recovery of acoustic impedance.
4. The seismograms after wavelet processing contain few low-frequency contents. Consequently, the acoustic impedance is not accurately reconstructed by the integral method.
5. The accuracy of acoustic impedance log is improved by addition of low-frequency contents of acoustic impedance log obtained from velocity analysis to high-frequency contents from seismograms after wavelet processing.
