Geological sequestration of CO 2 in a water-bearing reservoir in hydrate-forming conditions

Higher concentration of carbon dioxide in the atmospheric air is a major environmental challenge and requires immediate attention for quicker mitigation. In that respect, the novel idea of CO 2 sequestration in geological settings is worth examining from a quantitative perspective. In the present study, numerical simulation of CO 2 injection into a porous reservoir is performed. The selected reservoir presents suitable thermodynamic conditions for CO 2 hydrate formation. Unsteady simulations are carried out in one space dimension under isothermal and non-isothermal frameworks. An additional simulation of CO 2 injection in a depleted methane hydrate reservoir is also reported. In the present study, the response of the reservoir to storage of CO 2 is analyzed with respect to four parameters – reservoir porosity, initial water saturation and reservoir temperature and injection pressure. Quantities of interest are hydrate formation patterns and the cumulative CO 2 mass sequestration in the reservoir as a function of time. Numerical experiments show that the initial water saturation is an important parameter as it affects both CO 2 gas migration and hydrate formation. Isothermal simulation yields results that are similar to the non-isothermal model, thus suggesting that the isothermal assumption may be adopted for future CO 2 injection studies. Hydrate formation rate of CO 2 near the injection well is found to be one order of magnitude higher than the interior but its magnitude is quite small when compared to water and gas saturations. Higher injection pressure leads to a continuous increase in injected mass of CO 2 primarily due to increased gas density, though an increase in hydrate formation near the injection well is also observed. Lower reservoir temperature supports a higher amount of hydrate formation from the injected mass of CO 2 and is clearly desirable.