Numerical Analysis of CO2 Utilization As Hydrates in Depleted Natural Gas Hydrate Formation

Holding CO2 at massive scale in enclathrated solid matter called hydrate can be perceived as one of the most reliable methods for CO2 sequestration to mitigate devastating effect on climate change due to greenhouse gases outburst. CO2 injection in vacated natural gas hydrate porous sediment may form hydrate under low temperature and high pressure conditions but it seems very challenging on huge scale in lengthy formations.

In this study, a dynamically coupled mass and heat transfer mathematical model is developed which elaborates the unsteady behavior of CO2 flowing into porous media and converting itself into hydrates. The combined numerical model solution by implicit finite difference method is provided in which, CO2 phase transition, effect of hydrate nucleation by exothermic heat release and variations of thermo-physical properties has been studied during hydrate nucleation.

The results illustrate that formation pressure distribution becomes stable at early stage of hydrate nucleation process and always remains stable afterwards but formation temperature is unable to keep stable and varies during CO2 injection and hydrate nucleation process. Initially, temperature drops due to cold high pressure CO2 injection since when massive hydrate growth triggers and temperature increases under the influence of exothermic heat evolution. Intermittently, it surpasses formation initial temperature before CO2 injection initiates. The hydrate growth rate increases by increasing injection pressure in long formation and it also expands overall hydrate covered length in same induction period. The results also show that the injection pressure conditions and hydrate growth rate affect other parameters like, CO2 velocity, CO2 permeability, CO2 density, CO2 and H2O saturation inside porous medium. In order to enhance hydrate growth rate and expand hydrate covered length, injection temperature is reduced but it did not give satisfactory outcomes. Hence, by varying pressure and temperature conditions,hydrate-bearing sediment cannot be filled with hydrates in extended formations.