Dynamic characterization of shale systems by dispersion and attenuation of P- and S-waves considering their mineral composition and rock maturity

The dynamical elastic effective properties of gas-oil shale systems are found by using the self-consistent method and from them, dispersion and attenuation of P- and S-waves are calculated for a wide range of frequencies including seismic, sonic and ultrasonic bands. The mathematical model has the virtue of considering solid and fluid inclusions embedded in a matrix solid taking into account the volume fraction of each one. The mineral composition estimated from geological and petrophysical data is fed into the theoretical model in order to calculate the effective mechanical properties. The solid frame may be composed of clay, quartz or carbonate dominated lithotype; and the complement volume is occupied by pore fluids (water, heavy oil or dry gas), kerogen or solid inclusions. From that, typical patterns are established by the dispersion and attenuation of elastic waves in shale systems considering their mineralogy and maturity. In the acoustical branch, the results of the modeling have already been validated with laboratory data. Quartz and carbonate dominated lithologies exhibit very similar elastic responses and clay dominated lithotype shows a reverse reaction. These results are very useful tools to analyze and interpret the seismic response of target zones in oil and gas shale formations. Also, they aim to discriminate: drained, water-saturated, immature, mature or post-mature shale systems.