Seismic modelling of CO2 fluid substitution in a sandstone reservoir: A case study from Alberta, Canada

The prime objective of this study is to find the suitable petrophysical parameters which depict the maximum change in seismic amplitude due to fluid substitution. Therefore, in the present study the petrophysical parameters are analysed to detect the most sensitive parameters due to fluid substitution. The analysis is performed in three steps: In the first step, the Gassmann fluid substitution is performed and a considerable change in velocity, density, impedance, lambda–mu–rho parameters and Shuey’s parameters is examined. The study shows that the most sensitive parameters are A (intercept), which shows the maximum drop of 22% with respect to CO2 injection, and B (gradient), which shows the maximum increase of 10% with CO2 injection in the formation. Thereafter, in the second step, the seismic forward modelling is performed to examine the changes in seismic amplitude by the fluid substitution in the formation. The analysis depicts that the seismic amplitude increases steadily with increasing CO2 saturation. The amplitude increases by 4% at 20% CO2 injection, by 8% at 50% CO2 injection and the seismic amplitude increases by 12% at 100% CO2 injection in the target zone. Finally, in the third step, the numerical modelling is performed to assess the ability of seismic methods to detect the CO2 plume accurately by injecting CO2 plume of cylindrical shape. The analysis shows that the CO2 plume can be detected more prominently by analysing the impedance volume rather than the seismic amplitude section. This study is helpful in deciding which parameters should be monitored carefully in fluid replacement modelling projects.