New sights on derived behaviors of methane hydrate molecular structure in Na+/Cl- ions invading process

•NaCl ions are drove into MH phase via electric field to form metastable structures.•The structures evolution of Na+/Cl- hydrate shows randomness in invasion process.•Electrostatic field changed MH stability by effecting orientation of water molecules.•Free energy-barrier decreased in ions invasion process under the electrostatic field.•Na+/Cl- are hydrated in MH phase and have similar hydration shell with solution.