Synthetic modelling study of the effects of CO2 on p-wave attenuation

We present the results of a synthetic modelling study of the effect of CO2 on P-wave attenuation. Our theoretical model is made up of four horizontal layers. We computed synthetic seismograms from the isotropic model with no CO2 saturation and with the third layer of the model comprising of a porous material saturated with brine and CO2 at different concentrations. We used the spectral ratio method to compute the seismic quality factor, Q, from the synthetic data for crack densities of 0.01, 0.02 and 0.03 and fracture density of 0 at CO2 saturations of 0 to 100%. The results of our measurement indicate that attenuation is sensitive to CO2 saturation and the crack density. For a given crack density, attenuation increases gradually with decreasing percentage of CO2 saturation and reaches a maximum at 10% saturation. There is a rapid decrease between CO2 saturations of 10-30%. Also, the induced attenuation is observed to increase with crack density and offset. No noticeable attenuation is observed for the pure isotropic model with no cracks and fluid saturation.