Time-Lapse Numerical Modeling for a Carbon Capture and Storage (CCS) Project in Alberta, Using a Poroelastic Velocity-Stress Staggered-Grid Finite-Difference Method
A finite-difference algorithm was developed based on the Biot’s equations of motion to model seismic wave propagation in poroelastic media. As opposed to the elastic case, in the poroelastic approach the properties of the pore fluid are taken into account in the modeling process. Poroelastic modelling could be useful in cases where the fluid content of the rock is of interest, such as Carbon Capture and Storage (CCS) projects. The developed program was then used to investigate the detectability of CO2 in a CCS project in Alberta. Two models were defined for the baseline and monitor scenarios that respectively, represented the subsurface before and after injection of CO2 and the corresponding synthetic seismic sections were generated. The difference between the calculated seismic sections for the two scenarios shows that the residual amplitude is comparable with the baseline amplitude. With this result, the injected CO2 in the Quest project over a year could be detected providing the data have good bandwidth and a high signal-to-noise ratio. Furthermore, a comparison between the poroelastic algorithm and the elastic algorithm shows that the time-lapse effect in the poroelastic case is smaller than the one in the elastic case. In the fluid saturated media, some of the wave energy is dissipated due to fluid viscosity, and the poroelastic approach helps us to take this loss into account in the modeling process.