Seismic Wave Field Forward Modeling And Migration For The Fractured Reservoir

The dissertation focuses on seismic wavefield forward modeling and migration for the fractured reservoir. The paper integrates and researches the wavefield extrapolation operator for lateral variation of velocity, analysis of the wavefield characteristic, forward modeling and depth migration of prestack and poststack seismic wavefield, creation of wavelet, design of the model with fracture and cavity, and computation of reflectivity. In term of analyzing and summarizing the existing achievement, propose an advanced and practical wavefield extrapolation operator and arithmetic of forward modeling and migration, which obtain numerical simulation and analysis completely and systemically and exploited new field of fractured reservoir seismic wavefield numerical simulation and applicationin in frequency-wavenumber domain.Author, starts from the one-way wave equation of wavefield extrapolation, research the relationship and transform condition of wavefield extrapolation operators, and propose the steady variational reference slowness Rytov approximation general screen wavefield extrapolation operator(VRSELRF) which can adapt severe lateral velocity variations, in frequency-wavenumber domain, and the improved wavefield extrapolation scheme, also give the method to improve the computation efficiency. The achievement establishes the theoretic basis of the whole research. Author, secondly, starts from the approximate expandness of square root operator, perform mathematical calculations for finite difference operator in frequency-space domain, Fourier finite difference operator in mixing domain(frequency-space and frequency-wavenumber domain) and general screen operator in mixing domain, compare and discuss their precision of their wavefield, adaptability for lateral velocity variations, computation efficiency and stability.Thirdly, author, applies the steady variational reference slowness Rytov approximation general screen wavefield extrapolation operator(VRSELRF) in frequency-wavenumber domain, to the prestack and poststack forward modeling and depth migration. Comprehensively discuss the issues in application, adaptive condition and performance, propose a fast arithmetic of forward modeling and depth migration in common shot gathers with one-way acoustic wave equation based on VRSELRF, and verify the arithmetic by numerical simulation. Concisely discuss the cause of the creation of evanescence and the problem of lateral amplitude discontinuity result from it.Fourthly, use the reflectivity model, computed to describe the fracture model, with the formula of computation reflectivity based on elastic-acoustic approximation, and the wavelet model computed by the method, wavelet creation with Fourier Transform, we proposed, in conjunction with VRSELRF wavefield extrapolation operator. Further, analyse the characteristic of the seismic wavefield of fractural reservoir and the influence caused by fracture density, property of the filled material and the strike of fracture. Fifthly, in term of research of Zhangshulun et al., concisely discuss the arithmetic of the plane wave forward modeling and migration with phase shift method, in prestack common offset gathers and check the arithmetic by numerical simulation.