Direct Exact Nonlinear Broadband Seismic Amplitude Variations With Offset Inversion for Young's Modulus

Young's modulus and the Poisson ratio are critical for shale reservoir identification, and oil and natural gas detection since they are elastic parameters that can reflect the fracturing properties of subsurface rocks. The broadband inversion approach can make full use of the seismic ultralow-frequency information by combining it with the inversion results in the complex frequency domain. This plays an important role in the stability and reliability of the inversion, improving its resolution. Nevertheless, at present, the amplitude variation with offset (AVO) inversions of these parameters is mostly in the form of linear approximations, and there are few inversion methods of exact nonlinear equations or broadband. Considering that the nonlinear equation of reflection coefficient compared with the linear approximation has higher precision and fewer assumption conditions, and the low-frequency information of the complex frequency-domain inversion can improve the reliability of the inversion results, we derive an exact reflection coefficient equation for Young's modulus, the Poisson ratio coefficient, and the density based on the exact Zoeppritz equation and apply it to the broadband complex domain nonlinear prestack inversion. Young's modulus and the Poisson ratio coefficients estimated by the new inversion method provide a theoretical basis for evaluating the reservoir brittleness and compressibility, as well as a new approach for shale gas reservoir prediction and sweet spot identification. We tested the accuracy and rationality of this method with both synthetic and field data examples.

Automated summary

Young's modulus and the Poisson ratio are important parameters for shale reservoir identification and oil and gas detection. The broadband inversion approach combines seismic ultralow-frequency information with inversion results in the complex frequency domain, improving the stability, reliability, and resolution of the inversion. However, current amplitude variation with offset (AVO) inversions mostly rely on linear approximations, and there are few exact nonlinear or broadband inversion methods. We propose a new exact reflection coefficient equation based on the Zoeppritz equation for the inversion of Young's modulus, Poisson ratio, and density in the broadband complex domain. This method provides a theoretical basis for evaluating reservoir brittleness and compressibility, as well as a new approach for shale gas reservoir prediction and sweet spot identification. The accuracy and rationality of this method are validated using synthetic and field data examples.