Spectral decomposition and multi-frequency joint AVO inversion based on the neural network

The conventional AVO (Amplitude variation with offset) inversion method based on the amplitude attribute of pre-stack gathers calculates the elastic parameters of underground media through the variation of amplitude with offset. However, when the underground medium is a thin interlayer, the tuning effect will occur, which is the aliasing phenomenon of amplitude at the reflection interface. The tuning effect makes the conventional AVO inversion method based on amplitude attributes unable to solve the problem of thin interlayer recognition. In addition, the same reflection interface will have different AVO characteristics at different frequencies, whereas the frequency factor is not included in conventional AVO inversion methods. Two-stage neural network approaches based on deep learning are combined to improve the resolution of thin interlayers and to accurately invert the elastic parameters. For the first-stage neural network, a fully connected network is used to solve the inversion spectral decomposition problem. It can eliminate the thin interlayer tuning effect, effectively improve the resolution, and obtain reflection coefficients at different frequencies. For the second-stage neural network, a multi-channel convolutional neural network is used to establish the mapping relationship between multi-frequency reflection coefficients and elastic parameters, so as to the multi-frequency joint inversion of elastic parameters could be realized. The above procedure is applied to synthetic data (with and without noise) to show the anti-noise ability of the two-stage deep learning method. Compared with the method of directly predicting elastic parameters using seismic data and the conventional AVO inversion method, the two-stage deep learning method can describe the elastic parameters of thin interbeds more accurately. The same procedure is applied to the field data, and the inversion results indicate that they can well match with the well-logging data. Hence it is promising for practical applications. © 2023 Society of Exploration Geophysicists.