Molecular insights into ions permeation and destruction behavior in methane hydrate driven by electrostatic fields

Abstract

The formation and dissociation of gas hydrate can be promoted by different electrostatic field intensity, so it is considered as one of the potential technologies with great application value in hydrate exploitation, hydrate prevention in oil and gas wells and pipelines, and hydrate-related technologies. Generally, these technologies are used in the environment of ionic solution, resulting in the phenomenon of ion electrophoresis. The physical–chemical interaction between ions migration and hydrate is inevitable, but this interaction remains unclear. Herein, the crystal structure of methane hydrate infiltrated and destabilized by ions (K+, Na+, Li+, Ca2+, Mg2+, and Cl-) driven by electrostatic fields was shown through molecular dynamics (MD) simulation. Specifically, as the strength of the electrostatic field increases, the rate of diffusion and migration of ions in hydrate increases, accompanied by stronger destruction. Monovalent K+ migration is more effective in destroying hydrate structure under weak electrostatic fields, while divalent cations (Ca2+ and Mg2+) are more effective under strong electrostatic fields. The order of migration rate of ions in hydrate cages is K+ > Na+ > Li+ > Ca2+ > Mg2+. The difference of migration rate and destruction effect of ions in hydrate system is closely related to the hydration radius, hydration geometry, and hydration energy of ions. Dehydration and water molecular replacement occur in the process of hydrated ions driven by strong electrostatic fields entering the methane hydrate phase from the liquid phase. These molecular insights on the impacts of ions migration behavior on methane hydrate are beneficial for the application of electrostatic field in hydrate mining, safety of oil and gas pipeline transportation, and hydrate-related technologies.