Amplitude Variations of P-wave Reflection from Thinly Layered Porous Medium

In this study, both poroelastic and pure elastic forward modeling have been performed on reservoir models representing Class 1 and 3 amplitude-versus-offset (AVO) responses. Thin sand layers were periodically saturated with gas and water (White’s model). The reflection amplitude for both poroelastic and elastic models were calculated from the top interface of the thick reservoir and the amplitudes were studied as a function of frequency and incident angle. We found that in the seismic frequency range, the amplitudes for the poroelastic Class 3 AVO model increase when the frequency decreases. This trend is opposite to the elastic modeling result. For the Class 1 AVO model, however, the amplitude versus frequency trend is practically the same for both the poroelastic and elastic models. The numerical modeling results are explained by using White’s theoretical patchy-saturation model. The analysis of the modeling results might explain why soft reservoir rocks that are hydrocarbon saturated have low-frequency seismic anomalies.