Molecular Dynamics Simulations of Methane Hydrate Formation in Model Water-In-Oil Emulsion Containing Asphaltenes

摘要

Gas hydrate formation and asphaltene aggregation are two major concerns for flow assurance in the petroleum industry, whereas the atomistic understanding of their interactions remains limited, especially in the oil-dominated systems. Microsecond molecular dynamics simulations were performed to investigate the combined effects of solvent type, water droplet size, and asphaltenes on methane hydrate formation in a model water-in-oil emulsion by characterizing the four-body structural order parameter, molecular configurations, and evolution of hydrate cages. The results indicated the faster hydrate formation in a small water droplet with n-heptane because of the decreased interfacial curvature. Meanwhile, hydrate growth was promoted in a large water droplet with toluene because of the occurrence of a vertical water channel, which provided an extra growth site. The results also demonstrated the inhibition effect of asphaltenes on hydrate formation, which was more pronounced in a small droplet with n-heptane or a large droplet with toluene. This was attributed to two main processes that were closely related to the surface concentration of asphaltene at the oil-water interface, including the prevention of methane solution by the formation of an asphaltene shell and the disruption on local hydrogen-bonded networks by the formation of hydrogen bonds between asphaltene and water. Overall, the results provided theoretical support for a better understanding of the formation mechanisms of methane hydrates in asphaltene-rich water-in-oil emulsion, which was ubiquitous during the emulsification process of hydrate blockage in offshore subsea pipelines.