Stability and exchange of guest molecules in gas hydrates under the influence of CH4, CO2, N2 and CO2þN2 gases at low-pressures

Recovery of the gas from the hydrates demands a perturbation of the stable thermodynamic conditions, by thermal stimulation and depressurisation methods. The combination approach, however, has additional process complexities and demands a thorough knowledge of the geological conditions of the reservoir. Another approach is on the swapping of guest molecules within the hydrate lattice, and in theory the hydrates will not be subjected to dissociation. But the compatible guest molecule (CO2) will replace the caged CH4 molecule in NGH. Although the guest swapping mechanism is promising in the gas recovery process, an understanding of the process at the molecular level is obscure. In present study the existence of mixed hydrates, even under low-pressure environments, during the dissociation of CH4- or CO2-hydrates is demonstrated. The Raman spectroscopic signatures indicate the occurrence of mixed seed crystals even under lower pressures of exchangeable guests, through molecular diffusion process. The thermodynamic dissociation pattern unambiguously supports the rapid growth of mixed hydrates, depending on prevailing gaseous constituents. The CO2 molecules will diffuse into vacant/available cages in CH4- hydrates and vice versa. The nitrogen will act as a help gas in such diffusion process, and the specific Raman position (2328–2329 cm􏰂 1) indicates a lesser preference for encasing, while other two molecules are favourably encased into the available cages.

Citation

 

Pinnelli.S.R. Prasada,*, Burla. Sai Kiran; Journal of Natural Gas Science and Engineering 78 (2020) 103311; https://doi.org/10.1016/j.jngse.2020.103311