The Influence Of Fracture Parameters On The Seismic Wave Propagation And Complicated Fractured Model Construction

Fracture reservoir is the hotspot of the seismic exploration,it is benefit for reservoir characterization that the influence of fracture parameters on the velocity is predicted accuracy.However,it is hard to measure the fracture parameters(fracture density,fracture diameter,fracture aperture and fracture direction)in the reservoir.The modeling method can predict the relationship between the fracture parameters and the elastic velocity.On the other hand,the exist effective mdium need experiment validation.As for the multi-sets fracture formation,there is little of effective medium to describe the influence of fracture parameters on the elastic parameters.To investigate the fracture model experiments and effective medium construction can make a contribution to the fracture prediction in seismic exploration.The fracture density models and the fracture diameter models are used to measure the elastic wave velocities at three kinds of ultrasonic frequencies at lab and to analyze the influence of wavelength to diameter ratio on the elastic velocities.We compare the measured elastic wave velocities with Hudson theory and find that when the ratio between the wavelength and fracture diameter is larger than 7 for P-wave and 4 for slow S-wave,Hudson theory can be applied for the fracture diameter prediction.On the other hand,we measure the elastic wave velocities of crack density models and compare with the classic effective medium theories.We find that when the crack density is less than10%,the Hudson theory and the linear slip theory's predictions accord with measured P-wave and fast S-wave velocities,the Kachanov model and anisotropic SCA model accord with measured slow S-wave velocities.Furthermore,the higher the measured frequency is,the more they fit with each other.By using the spectra ratio method which eliminates the diffraction effect,we quantitatively investigated the scattering attenuation caused by the crack density and fracture aspect ratio.Through the crack density models,the P-wave attenuation in the direction perpendicular to the fractures is larger than the direction parallel to the fractures with increasing the fracture density.However,the attenuation anisotropy at the low fracture density is more sensitive than that at the high fracture density.The attenuation anisotropy is larger than the velocity anisotropy for the fracture density models.Through fracture aperture models,we study the scattering effect and fracture aspect ratio on the P-wave attenuation and compare the measured attenuation with Kawahara model,we find that measured P-wave attenuation is accord with Kawahara model very well on the 1 MHz measured frequency.As for the TI background matrix permeated by vertical fractures,based on the effective compliance is the linear sum of the background matrix compliance and the fracture excess compliance,by introducing Gaussian function to describe the vertical fracture clusters,we give the analytical expression of the effective compliance and create a monoclinic medium.As for two kinds of effective ORT medium,based on Chapman multi-sets fracture model,we compute the orthogonal fracture excess stiffnesses,construct a porous ORT medium,and give the analytical expression of Thomsen anisotropy parameters.For the effective medium composed by TI medium and VFTI medium,we apply BCH series to extend the Backus averaging method to the low frequency range and prose the analytical kinematic parameters expressions of the effective ORT medium based on the linear slip theory.