Impact Of Meso-scale Wave-induced Fluid Flow On Seismic Propagation In Poroelastic Media

In the field of seismic petrophysics, velocity dispersion and attenuation phenomenon is a significant theoretical basis to expand the reservoir and fluid prediction in frequency domain and the fluid prediction. Wave induced fluid flow(WIFF) relates the transportation parameters and seismic signal together. Meso-scale is a length between pore scale and wavelength. The inhomogeneous of mesoscopic is the principle cause of attenuation in seismic frequency band. The content of this dissertation is arranged as follows.(1).Biot attenuation mechanism and three kinds of mesoscopic attenuation mechanism(mesoscopic fracture model, double-porosity model, interlayer-flow model) are introduced.(2).Analytical solution of interlayer-flow model. The quality factor is characterized by frequency, s(determined by flow parameters, viscosity and permeability) and g(determined by elastic modulus and porosity).The approximation of quality factor is deduced. The approximation is in good agreement with analytical solution at high frequency limit and low frequency limit.(3).Impact of parameters(e.g., viscosity, permeability, fluid mobility, porosity, etc.) on quality factor Q(ω) and phase velocity Vp(ω). Seismic trace is simulated. The results could be obtained:①the main attenuation procedure occur in low frequency band;②Greatly attenuation happened when obvious fluid properties are different between two layers;③With increasing of viscosity, the peak frequency moves towards low frequency, while attenuation reduces;④With increasing of permeability, the peak frequency move towards high frequency, while attenuation do not change;⑤With increasing of porosity in consolidated reservoir, the peak frequency move towards low frequency.⑥With increasing of fluid mobility, the peak frequency move towards high frequency, while attenuation do not change. The permeability have greater influence than viscosity.(4). Influences of matrix moduli and porosity on maximum attenuation and peak frequency are studied when rock saturated with different fluids.①.When maximizing the matrix moduli and porosity of layer L2, maximum attenuation of partially gas saturated media> maximum attenuation of partially oil saturated media > maximum attenuation of full water saturated media. While, peak frequency of full water saturated media> peak frequency of partially gas saturated media> peak frequency of partially oil saturated media.②. When minimizing the matrix moduli and porosity of layer L2, maximum attenuation of partially gas saturated media> maximum attenuation of partially oil saturated media > maximum attenuation of full water saturated media. While, peak frequency of partially gas saturated media>peak frequency of full water saturated media> peak frequency of partially oil saturated media.(5).Influence of fluid saturation on reflectivity. We use approximate formula of White’s model analytical solution to investigate the reflectivity between attenuation layers embedded in elastic layer. Then obtain effects of attenuation and tuning to reflectivity. The result of numerical simulation is compared with laboratory measurements. Experimental data of water-saturated sandstone and dry sandstone adapted to unconsolidated sandstone which partially saturated with water. The results indicate that low-frequency anomaly related to fluid saturation can be explained by WIFF. The reflectivity of partially saturated reservoir is frequency-dependent.