Natural gas exploitation by carbon dioxide from gas hydrate fields - high-pressure phase equilibrium for an ethane hydrate system

Natural gas hydrate fields, which have a large amount of methane and ethane deposits in the subterranean Arctic and in the bottom of the sea at various places in the world, have become the object of public attention as a potential natural gas resource. Here the idea of natural gas exploitation from natural gas hydrate fields combined with CO2 isolation using CO2 hydrate has been presented. As a fundamental study, high-pressure phase behaviour for the ethane hydrate system was investigated in a high-pressure cell up to a maximum pressure of 100 MPa, following a previous study of CO2 and methane hydrates. Consequently, the phase equilibrium relationship of an ethane hydrate-water-liquid ethane mixture was obtained in the temperature range from 290.4 to 298.4K and over a pressure range of 19.48 to 83.75 MPa. The observed phase boundary corresponds to the three-phase coexisting line with a non-variant quadruple point of ethane hydrate-water-liquid ethane-gaseous ethane at 288.8 K and 3.50 MPa, similar to the CO2 hydrate-water-liquid CO2 system.