Seismic modeling of fluid substitution in Redwater Reef, Alberta

Taher M. Sodagar, Donald C. Lawton

The objective of this study is to analyze and undertake seismic modeling of CO₂ saturation of the Devonian Leduc reservoir characterization at the Redwater reef by using Gassmann fluid substitution seismic modeling. This method was applied to the available wells inside the reef. Zero-offset synthetics were created for these wells before and after fluid substitution.

A distinct P-wave velocity decrease occurs from 0% to about 40% of CO₂ saturation. From around 40% to 100% of CO₂ saturation, the P-wave velocity starts increasing slightly, while the S-wave velocity increases almost linearly with the CO₂ saturation increase. There are slight changes in amplitudes between the wet in-situ reservoir reflections and the fluid substitution modeling reflections of Leduc formation. A time shift is observed at the base of the Leduc reservoir. The maximum time shift at the base of the Leduc reservoir and the highest amplitude difference changes are recognized at around 40% of CO₂ saturations.