MOLECULAR DYNAMICS STUDIES OF THE STABILITY OF CO2 AND CH4 HYDRATES IN THE PRESENCE OF UNDERSATURATED FLUIDS

Methane hydrates are globally distributed in sediments along the continental margins and potentially contain more energy than all fossil fuel reserves. However, methane is also a potential greenhouse gas which could play a major role in global climate change. Accurately characterizing the stability of methane and CO2 hydrates in water can help us understand their effects on earth’s environment and also fesibilty of long term CO2 sequestration in the sediments under the ocean floor. Hydrate stability can be better predicted by understanding the phenomena related to hydrate dissolution in water. Under hydrate stability conditions, the concentration difference between the hydrate and water phases of hydrate-forming gases should be an important factor affecting hydrate stability as oceanic hydrates are exposed to under-saturated sea water. In this work, the dissolution of methane and CO2 hydrates have been studied and compared to one another in the presence of water using molecular dynamics simulations. The average lattice constant for structure I and II hydrate was calculated for two different potentials of methane OPLS and GROMACS and compare to the experimental value for validation. Methane hydrate dissociation in the presence of water was also studied using these two potentials in addition to the Anderson et al. model. The Harris and Yung model for CO2 as well as our own ab initio-derived CO2 potential were used in the simulations of CO2 hydrate in the study. In order to provide comparison of the CO2 potentials, the reference chemical potentials, densities of pure CO2 liquid and vapor, and solubility of CO2 in water were calculated using each of the potential models