Frequency Dependence Of Elastic Properties In Fracture Porous Medium And Impact Parameters

The complex reservoirs like fractured reservoirs are the major research aspects at present.These researches are based on the effective fracture media models,and appropriate forward modeling method to simulate the seismic response of fractured media and analyze the influence of sensitive parameters on seismic attributes.These works play important role in the exploration and development of oil and gas resource.Based on these ideas,the main works of this paper are as follows:(1)The staggered grid finite difference technology with the characteristic of fast calculation and high efficiency,can simulate the seismic wave propagation from underground media quickly.This paper,derived wave equation and the first-order velocity stress equations of different media,used the staggered grid finite difference technology,conducts the forward modeling of a variety of medium like the isotropic medium,the anisotropic medium,the viscoelastic medium,the Two-phase medium(the Biot theory and the improved BISQ theory).Through the result of the wave field snapshots and seismic record,one can found that the shear wave splits in anisotropic medium,and in the forwarding modeling of the two-phase medium,slow compressional wave occurs,and the slow compressional wave in the solid phase is different from that in the liquid phase.(2)Three equivalent models of fractured media,including Hudson model,linear slid model and Thomsen model,are introduced in this paper.These models,however,do not take the background porosity and the fluid's impact into consideration.Gurevich,who considers the background porosity and combines Gassmann anisotropy equation and the linear sliding model,comes up with a double-porosity fracture model.Based on Gurevich's equivalent fracture medium model,this paper analyzes the influence of background porosity,fracture density and fluid type on seismic wave propagation under low frequency limit.According to the simulation results,with the increase of fracture density and background porosity,the anisotropy of the medium increases,while with the increase of the bulk modulus of the fluid,the anisotropy of the medium decreases.The simulation results are the same with the result of the theoretical calculation.(3)In mesoscopic scale,this paper analyzes dependent frequency of the elastic properties in fractured porosity medium.In order to study the causes of the dispersion and attenuation in the fractured media,based on the Brajanovski model,this paper analyzes the influence of the fracture weakness and background porosity on the Pvelocity in the whole frequency band.The results show that the velocity dispersion and attenuation have a shape typical for a relaxation phenomenon,and the degree of dispersion and attenuation increases with the increase of porosity.When the porosity is close to 0,the phase velocity does not substantially disperse and attenuate.With the increase of the fracture weakness,the degree of attenuation and dispersion increases,and the peak of attenuation moves toward low frequency.(4)In microscopic scale,this paper based on the Collet model(squirt flow model),calculates the phase velocity and inverse quality factor of dependent frequency under different incidence angles,and analyzes the impacts of porosity,fracture's density and fluid type on seismic attributes.