The exchange between clathrate phase and gas phase methane on artificial methane hydrate

The exchange of methane between clathrate phase and gas phase on artificial methane hydrate was studied. Artificial methane hydrate samples were formed in a pressure cell from methane gas with stable carbon isotope composition δ13C of －42.3‰（ methane A）. Methane A remaining in the gas phase was removed from the cell at 77 K and methane gas with stable carbon isotope composition δ13C of －66.9‰（ methane B） was introduced into the cell. The carbon isotope compositions of both clathrate phase and gas phase methane gases were measured after the samples had been maintained at 274.7 K for 7-50 days. The δ13C of the clathrate phase methane was smaller than the initial value of －42.3‰ and that of the gas phase methane was larger than its initial value of －66.9‰. These results suggest that the exchange between the clathrate phase and gas phase methane proceeded in the period of the scale for several weeks.