The Sensitivity Analysis Of Clay-rich Porous Medium

Porosity, clay content, saturation, temperature, pressure and permeability are always critical parameters in time-lapse seismic studies. There is less study clay content than other parameters because of the complexity of clay. There is no effective method to study clay content yet. In order to study the variations sensitivity of clay-rich porous medium, I built petrophysical model on the basis of the latest results of petrophysics and derived Gassmann's equation with effective porosity under high clay content. Then PP and PS wave reflection coefficients can be obtained from fluid substitution model based on Gassmann theory and the simplified AVO equation. Finally, we carefully studied how sensitivity of clay content, temperature, pressure and permeability to reservoir density, velocity, reflection coefficient in porous medium.Our study shows that①By analyzing and comparing the research results of low clay content and high clay content, we found that P-wave velocity is more sensitive to the variations of high clay content. P-wave velocity had decreased more in high clay content than that in low clay content. S-wave velocity is more sensitive to both porosity and clay content and S-wave velocity decreased with the increasing in porosity and clay content. But S-wave velocity variations is less than that of P-wave velocity.②With the increasing in clay content, the absolute values of PP and PS wave reflection coefficients were in inverse ratio to clay content. Namely, the more clay content, the less the absolute values of PP and PS waves reflection coefficients. By comparison with low clay content cases, PP and PS wave reflection coefficients decreased more under the effect of high clay content.③Given different temperature, P-wave velocity is more sensitive to the variations clay content. factor of high clay content had a more influence on PS wave reflection coefficient is more sensitive to high clay content with temperature increase.④Although, P-wave velocity had increased with the increasing of pressure, but overall, P-wave velocity did not increase significantly under the effect of high clay content. Under the effects of pressure, PS wave reflection coefficient is more sensitive to high clay content.⑤P-wave velocity is increasing with decreasing of clay content and increasing of permeability.