Research On The Seismic Wave Propagation In Complex Porous Media

The research of seismic waves propagation in porous medium is one of the hotspot in the field of Geophysics and petroleum Exploration research. Problems of these kinds of porosity come from the different-scale coupling effects between pores, fractures, caves and solid skeletons. Current work is focused on seismic attenuation mechanism in porous rocks, and the remaining problems include physical description and numerical simulation about complex porous rocks. This thesis analyzes the skeletion-relaxed mechanism and the diffusion-relaxed mechanism in porovisco- elastic medium, and simulates the wavefields through a pesudo-spectral method in the double-porosity rocks with mesoscopic fluid flow(MFF).Actual reservoir rocks are anelastic materials, especially when they are saturated with some kind of fluid, which will make the viscoelastic characteristics more significant. In the poroviscoelasticity theory, the relaxation effect is considered based on the Biot's theory. Three parameters of P wave quality factor, S wave quality factor and diffusion quality factor are introduced to describe the relaxation effect in porous medium. A pseudo-spectral method is used in forward modelling, and simulation results disagree with Carcione's points(1999, 2006). Low-frequency poroviscoelastic modelling shows that the skeleton-relaxed mechanism can also be used to describe the seismic band attenuation for elastic waves. It has the physical meaning of mesoscopic relaxation effect between the small grain particles.Furthermore, the thesis also studies the problems in seismic denoising and parameters inversion to assess a relaxed solid skeleton's influence on low frequency band attenuation. In the denoising and preprocessing for seismic inversion, a zero-crossing filter is developed based on wavelet analysis to remove surface waves from the multi-component seismic data. Niche Genetic Algorithms Inversions on the numercial models and actual seismic records from east China show that shallow layer soil has a viscoelastic nature in solid particles, and its quality factor can be directly estimated from observation. The inversion also proves the skeleton-relaxed mechanism's reasonability and validity.To investigate the intrinsic relationships between seismic attenuation and pore fluid flow, the thesis derives the Biot's absolute displacement form of the wave equations in double-porosity rocks, and provides a discrete algorithm to numerically solve the fluid increments caused by MFF. Wavefield is simulated in double-porosity rocks with MFF and Biot diffusion, and the three models are compared in the numerical experiment, which include model with none fluid flow, model with MFF, and model with MFF and Biot flow. Results show MFF will transfer the fast waves'energy to slow waves, and the high attenuation of the second kind of slow P wave can be explained with the Biot diffusive mode.