Sensitivity Analysis of Petrophysical Parameters Due to Fluid Substitution in a Sandstone Reservoir

Abstract

In the present study, the CO₂ storage potential of a subsurface sandstone layer of the Blackfoot field, Alberta, Canada, is evaluated. In this study, seismic reservoir monitoring has been performed to monitor fluid flow effects in seismic amplitudes. In order to monitor CO₂ fluid viability, the Gassmann fluid substitution analysis is also performed to analyze the seismic amplitude response along with the seismic forward modeling which is used to generate seismic data from the geological model. From the seismic forward modeling, a significant variation in seismic amplitude is recognized due to fluid substitution. From the Gassmann approach, considerable changes in P-wave and S-wave velocities, densities, and impedances are observed with increasing CO₂ saturation. From the results, it is observed that the sudden drop in acoustic impedance occurs between 0 and 20% CO₂ saturation and that leads to the detectable time shift at the top of the CO₂ plume. Further, amplitude versus offset (AVO) and Lambda-mu-rho (LMR) analyses have been performed to demonstrate the detectability capacity of these parameters due to the change in fluid saturation in the porous media. In addition, time delays at the injected reflector are also measured. The changes caused by the CO₂ plume in the seismic section are also identified by subtracting the monitor model (CO₂ saturated model) from the baseline model (0% CO₂ saturated model) in time domain as well as in impedance domain. The proposed amount of CO₂ injection is considered as 10⁵ tonnes for one year of injection. The study demonstrates that the CO₂ plume can be detected in a more detailed way with very high resolution by working in impedance domain rather than working in time domain.