Molecular dynamics simulation of methane hydrate formation on metal surface with oil

Abstract

Microsecond molecular dynamics simulations were performed to investigate the methane hydrate formation on smooth and rough metal surface covered with water, light oil, and heavy oil with asphaltenes, respectively. The growth and crystallization of methane hydrates were characterized by the four-body order parameter and the face-saturated incomplete cage analysis. Results highlighted the priority for hydrate growth inside the groove of rough metal surface, from which the hydrate grew upwards to the outside of the groove and then to the water-gas interface. It clearly demonstrated the inhibition effects of light oil on the methane hydrate growth, which was further enhanced by adding asphaltenes. The inhibition mechanisms were elaborated during different stages of hydrate growth by gaining insights into the four-body order parameters at different locations of metal surface. To our knowledge, this was the first molecular-level study on the methane hydrate evolution on metal surface with heavy oil. It provided theoretical supports for evaluating the priority sites for the hydrate formation on pipe wall with concaveandconvex surfaces that might result from metal corrosion, change of pipe diameter or depositions of solid particles during the multi-phase transportation.