Impurities such as H2S and SO2 play important roles in dissolution trapping mechanisms in geological sequestration of CO2. In this study, a pore-scale numerical investigation of the convective mixing process in geological storage is conducted using the lattice Boltzmann method. Tests with a different value of diffusivity ratio RD and buoyancy ratio of the impurities RβRC are considered. Theoretical analysis demonstrates four distinct scenarios of initial diffusive density distribution, including the monotonic and nonmonotonic density distributions along the gravity direction. Numerical results show that the general phenomena of the mixing processes are quite different in different scenarios. In particular, when the density distribution is nonmonotonic, the intensity of the system's convective mixing will be weakened by the density stratification structure. At the same time, the time evolution of the dissolution flux is also affected by impurities correspondingly, leading to some differences from the pure-CO2 system. In addition, the onset times of convection for different impure systems are also investigated. For a given Rayleigh number, the system is less prone to gravitational instability compared to that with only CO2, when RβRC<0 and the onset time will be prolonged correspondingly. In order to assess the strength of convection in an impure system, an effective Rayleigh number Rae is defined in this paper, where the influences of impurities are taking into account. According to the simulation results, the onset time ton can be well fitted as ton∼Rae-2, which is consistent with the role of the Rayleigh number in a pure-CO2 system.
ASJC Scopus subject areas
- Computational Mechanics
- Modeling and Simulation
- Fluid Flow and Transfer Processes