Prestack Seismic Inversion With Inverse Operator Estimation

Prestack seismic inversion is widely utilized in exploration geophysics because of its abundant information,especially for reservoir prediction and fluid identification.During the process,there are 3 important factors that influence the inversion results:inversion algorithm,forward model,reflection equation.This paper puts forward the corresponding improvement methods for the above three aspects.Model test verifies the feasibility of the methods,the actual data application indicates that the method improves the accuracy of fluid identification.As for the inversion algorithm.The traditional inversion algorithms are mainly optimization,while the AVO inversion based on inverse operator estimation is to inverse directly.The key is to find the subspaces which exist inverse mapping instead of searching for the solution directly as optimization algorithms do.Then inverse operator estimation in trust region that guarantees the stability and efficiency as well is applied for solving AVO inversion problem,in which optimization and inverse directly are integrated.Seismic signal can be considered as the convolution of reflection and wavelet,the wavelet amplitude remains unchanged.This paper proposes a modified convolution model in which transmission loss will be integrated into convolution by the performance of the wavelet amplitude attenuation,modified convolution shows more realistic characterizations of the seismic signal forming process.For the reflection equation,different reflection equations need to be used for different geological backgrounds.First in this paper,a nonlinear inversion method is proposed for the strong difference interface.High-order Zoeppritz approximation is utilized to establish the inversion objective function in which variation of V_P/V_S with time is taken into consideration.Then a new fluid factor K_R for solid-liquid decoupling is constructed for the complex pore reservoir.Equivalent fluid bulk modulus K_R is more sensitive to different types of fluid within the pores of rock than conventional fluid factor.Pre-stack seismic inversion can effectively get equivalent fluid bulk modulus.The Zoeppritz approximate and elastic impedance equations are derived.Direct inversion is realized based on elastic impedance equation of equivalent fluid bulk modulus.At last,a two term approximation for density inversion is proposed for density inversion.