Fractured Media Avo Sensitivity Analysis

Saturation, permeability and pore pressure are always critical to develop oil and gas field development and evaluate reservoir. This thesis was built on Hudson's theory, on the basis of the latest achievements in the world. By rock physics method, we had built the certain relation saturation, permeability and effective pressure model with seismic wave velocity, anisotropic parameters and seismic wave amplitude in cracked medium. Based on the relationship above, we studied the variations sensitivity of seismic wave velocity, anisotropic parameters and seismic wave amplitude versus saturation, permeability and effective pressure.Our study shows that seismic P-wave velocity and amplitude have obvious advantages in detecting saturation when the stratum inclination is small; but converted wave amplitude has the same ability at longer offset. In the fractured stratum, the anisotropic parametersεandδhave good relativity with water-saturation, the anisotropic parameterγhas not correlation with them. The linear relationship does not exist between seismic wave velocity and their permeability. If crack density of crack rock is less than 0.13, seismic wave velocity does not relate to the permeability, if crack density ranges from 0.13 to 0.41, the permeability is the approximate cubic function of crack density, if crack density exceeds 0.41 the permeability is the approximate linear function of crack density. The sensitivity of P-wave detecting permeability always depends on the fluid character in crack. PP-wave amplitude can reflect the change of permeability in gas cracked sandstone, but they can't reflect permeability in oil (wet) cracked sandstone. By comparison with PP-wave, PS-wave is insensitive to the character of fluid in crack and becomes the ideal tool of detecting change of permeability. PS-wave amplitude always reflects the change of permeability both in gas cracked sandstone or in oil (wet) cracked sandstone. In middle or large offset, PP-wave and PS-wave are more sensitive to pressure; they in the gas cracked sandstone have an advantage over in the oil (wet) cracked sandstone.