Effect of impurities on the onset and growth of gravitational instabilities in a geological CO2 storage process: Linear and nonlinear analyses

- Effects of impurities such as H2S, N2 and SO2 on solubility trapping are analyzed theoretically.
- New stability limits are obtained by considering a non-monotonic density profile.
- Negative rβrC- impurities retard the onset of instability and lower dissolution rare.
- Time-periodic oscillatory motion is not observed.

Because 75% of the total cost of carbon capture and storage (CCS) arises from the separation of CO2 from gas streams (Nsakala et al., 2001), the co-injection of CO2 and impurities such as H2S, N2, and SO2 is considered a cost-effective alternative to pure CO2 geological sequestration. Here, the effect of the impurities on the onset of gravitational instability has been analyzed theoretically and numerically. Linear stability equations have been derived and solved analytically and numerically. Double diffusive effects make the system stable or unstable depending on the values of the diffusivity ratio, δB, and buoyancy ratio, rβrC. In addition, using the Fourier spectral method, we have traced the temporal evolution of the gravitational fingers numerically. The shape and the growth history of the fingers are strongly dependent on the impurity content. The time-periodic oscillatory motions are not observed in the present linear and nonlinear analyses. For a given Rayleigh number, the dissolution of N2 and H2S impurities makes the system stable, whereas dissolved SO2 accelerates the onset of instability.