Study On Seismic Wave Dispersion Response Of Fluid-saturated Porous Rocks

During the propagation of seismic waves in reservoir rocks,the fluid flow in pores will cause velocity dispersion and attenuation,thus affecting the seismic response characteristics of reservoir.Seismic rock physics establishes a quantitative relationship between reservoir properties and seismic attributes.Theoretical models based on different fluid flow mechanisms describe the effects of fluid properties,saturation,and permeability on velocity dispersion and attenuation.On the other hand,the forward modeling methods in the frequency domain use the dispersion velocity to link the reservoir properties to the seismic response.Mesoscopic fluid flow is usually caused by the heterogeneity of partially saturated fluid properties or rock frame properties.Both types of heterogeneity are much larger than the pore size and smaller than the wavelength.The corresponding dispersion and attenuation mainly occur in the seismic frequency band,having a significant impact on seismic response.This paper reviews and implements the White periodic layered patchy saturation model,one-dimensional and three-dimensional random patchy saturation model,horizontally oriented fracture model,explores the corresponding velocity dispersion and attenuation characteristics of each model,and analyzes the anisotropic characteristics of fracture model and layered patchy saturation model.Microscopic squirt flow is caused by the difference in compressibility of soft and stiff pores,which mainly occurs in the sonic and ultrasonic frequency bands.In this paper,a simple squirt model is used to explore the effect of partial saturation of soft pores on frequency dependent dispersion and attenuation,and the high and low frequency limits of the modified frame considering the distribution of soft pores are analyzed and discussed.The mesoscopic and microscopic fluid flows occur in different frequency ranges,but the two influence each other.At the same time,the single-scale theoretical model is not suitable for the interpretation of full-band experimental data.Therefore,replace the dry frame modulus of the patch saturation model or fracture model with the modified frame modulus of the squirt flow,and a scaled fluid flow model with multiple attenuation mechanisms was established;the background medium P-wave modulus of the fracture model was replaced by the ones of the patchy saturation model or the scaled model,acquiring a unified model.At the same time,the new theoretical models are used to interpretation the experimental data of predecessors.Based on the approximate expression of the single-interface normal incidence reflection coefficient considering the reservoir velocity dispersion and attenuation,the sensitivity of the dispersion property of the reflection coefficient to fluid saturation and porosity is analyzed.The propagation matrix multi-interface reflection coefficient calculation method was used to analyze the influence of reservoir attenuation on seismic records.According to the frequency domain optimization nine-point finite difference forward method,the effect of considering reservoir dispersion on the time,amplitude and phase of the reflected wave at the bottom of the reservoir is analyzed.