The Study On Seismic Forward Modeling Based On The Rock Physics Of Fracture Media

The fluctuational anisotropy widespreads in the earth media,mainly in the seismic anisotropy of seismic wave propagation velocity being a function of the direction of propagation,the mutual coupling between body waves,splitting of shear waves and so on.Fractured media is not only an important channel for migration of gas and oil,it is also important storage space for gas and oil,so that more and more attention is paid on the field of exploration of oil and gas.Azimuthal anisotropy media includes HTI(horizontal transverse isotropic)media,orthohombic anisotropy media and monoclinic anisotropy media and so on.Based on the theory of equivalent fractured media rock physics bridges are built between physical properties of fracture media and feature of anisotropy medias,according to the theory of linear slip,Thomsen theory and Hudson theory,we use fracture density,aspect ratio,filling of fracture and other physical properties to calculate the stiffness matrix of HTI media,orthohombic media and monoclinic media,providing models for the elastic wave forward modeling in three-dimensional azimuthal anisotropy media;stiffness matrixs of three medias above are changed into dimensionless anisotropy parameters,providing models for the qP wave forward modeling in three-dimensional azimuthal anisotropic media.With the constitutive equations,geometric equations and differential equations of motion,the three-dimensional first-order velocity-stress wave equations of the HTI media,orthohombic media and monoclinic anisotropic media are derived.And then these elastic wave equations are solved through high order staggered grid finite difference to simulate the propagation process in these medias.During the process of modeling,the wavefield characteristics under the conditions of different physical properties of fractures are analyzed,as well as azimuthal characteristics of orthorhombic and monoclinic anisotropy.The research resultses show that the anisotropic strength are related to fracture density,and these characteristics are reflected in the CSP sets and forwarding wavefield.The method of least squares and time-space domain dispersion relation are applied to elastic wave forward in the above medias to derived new difference coefficients,model tests show that these methods can reduce the numerical dispersion phenomenon effectively and improve the accuracy of the differential significantly.The Christoffel equations of three fracture medias are drived,according to the acoustic approximate thought,we drive three-dimensional high-order qP wave equation of three fracture medias,and then drive three-dimensional one-order qP wave equation.The qP waves in the actual three-dimensional models of complex fracture are simulated,we also analyze influence of fracture properties on the propagation of seismic wave.The excitation amplitude imaging condition is applied in the RTM of the fractured media,,which significantly reduce data storage and I/O,improving imaging efficiency and effects.