The effect of porosity on the seismic waves velocities and elastic coefficients in a South-Western Iran''''s oil field

Abstract

Petrophysical and geophysical laboratory measurements were performed on ⁽40⁾ samples made of sandstone and limestone in an Oil Field. Parameters including porosity, density and permeability were measured along with the of compressional and shear waves’ velocities of the samples under reservoir conditions. Also, the study of microscopic thin sections, factors affecting the velocity of waves including porosity, Poisson’s ratio, density, pressure and pore type were investigated. The scattering of points in the velocity diagrams of elastic waves based on the petrophysical parameters of the rock indicates that the most important factor of velocity changes is the pore type in the samples in the same porosity value. So, ‹LMR› parameters were calculated using laboratory results of velocity measurement. The values of ‹LMR› parameters of seismic data were determined by the velocities of compressional and shear waves in the pre-stack stage seismic. Then, using seismic inversion, compressional and shear wave resistances were estimated and seismic sections with ‹λ.μ› and ‹μ.ρ› parameters were created. The results show that there is a good correlation between laboratory measurement of rock physics and pre-stack seismic data. Also, the factor affecting the velocity of waves, i.e., the pore types, should also be considered. Uncertainty in velocity values due to the diversity of pores can show differences in the velocity of elastic waves in the same porosity value to about ⁽1500⁾ m/s. Also, at a constant velocity, porosity changes of up to ⁽20⁾ percent are visible.

Keywords

• compressional and shear waves velocities
• poisson’s ratio
• lame coefficients
• pre-stack
• pore types