Molecular simulation study on the effect of cosine oscillation electric field in methane hydrate reformation process

Methane hydrate reformation process appeared in solid hydrate storage and gas exploitation pipelines, where hydrate acceleration and preventation were required, respectively. Cosine oscillation electric field with property of adjustable parameters (intensity and frequency) could be a potential method to control hydrate growth. Molecular dynamics simulation was employed to investigate the effect of alternating electric field in methane hydrate reformation. The hydrate growth rate, bubble evolution, move of CH4 molecules and hydrogen bonds were obtained by calculating the four-body structure order parameter, distance of CH4 molecules, average move distance of CH4 at specific location and the bonded water pairs, respectively. The results showed that cosine oscillation electric field caused fastened hydrate formation, dissociation or weakened formation process with frequency increased from 1 THz to 70 THz. The dual effect was due to reciprocating motion of water and the alteration of hydrogen bond under condition of specific field frequency, which led to suitable move step of CH4 or cage destruction. In system with (1 ∼ 9) THz frequency, suitable move step (0.5 nm/ns to 0.8 nm/ns) of CH4 and the mutually reinforcing effect between the incomplete cage and nearby gas jointly brought out the fast cage building and gas encage.