Wave Field Simulation And Characteristic Analysis Of Biphasic VTI Medium

The actual formation,especially the reservoir is usually a rock multiphase system consisting of a solid phase and a fluid phase.Moreover,the solid skeleton of reservoirs often exhibits anisotropy,and the pore-filled oil and gas often occurs in fluid form in the reservoir.The traditional elastic wave theory is based on single-phase solid medium,which cannot accurately explain the seismic data and describe the actual underground medium.Therefore,considering the two mechanisms of anisotropy and pore fluid,a more accurate geological model can be established.Numerical simulation studies on the above are of great practical significance for the exploration of increasingly complex reservoirs.Therefore,it is necessary to study the propagation law of elastic waves in a two-phase anisotropic medium.Based on the previous studies,constitutive equations,geometric equations and equations of motion,the elastic wave equations and first-order stress-velocities of single-phase VTI media,two-phase isotropic media and two-phase VTI media are demonstrated.The wave equation is introduced.The finite difference method of staggered grid is introduced.The difference scheme,boundary conditions and stability are discussed.Then the eigen-boundary boundary of the perfectly matched layer is selected and solved by time-order second-space eight-order staggered grid finite difference method.The first-order stress-wave equation of the above medium is used to realize the wave field simulation.The wave field snapshot obtained by forward modeling is used to analyze the response of the solid-state elastic parameters and the flow-phase parameters to the elastic wave in the above medium,and establish a number of matches.The actual medium model is used to study the reflection and transmission phenomena of elastic waves at the wave impedance interface.The results show that the elastic parameters affect the morphological characteristics of the elastic wavefront in the medium,whether it is a single-phase VTI medium or a two-phase VTI medium.In the two-phase medium,the fast and slow longitudinal and transverse waves reflect at the wave impedance interface.There is a mutual conversion between the modes during transmission,which is consistent with the prediction of the wave field characteristics of the two-phase medium in the theory of Biot.