Electrical Resistivity Measurements of Methane Hydrate during N2/CO2 Gas Exchange

Natural gas hydrates, known to exist in both continental margins and permafrost regions, have received tremendous attention, owing to their potential use as an unconventional natural gas resource. Among the options to develop natural gas hydrates, a gas exchange method using an external CO2 or N2/CO2 mixture is considered one of the most promising technologies because (i) the process can prevent structural destruction of the gas hydrate deposits by swapping CO2 or N2/CO2 for CH4 molecules and (ii) injected CO2, a global warming gas, can be sequestered and locked away through the formation of thermodynamically stable CO2 or N2/CO2 hydrate. During and after N2/CO2 injection, however, the progress of gas exchange and the stability of the mixed CH4/N2/CO2 hydrate must be monitored. In this study, the electrical resistivity of CH4 hydrate before, during, and after N2/CO2 swapping was investigated using a lab-constructed tube-type reactor system for in situ electrical resistance measurement. The natural environment of a gas-hydrate-bearing sediment was simulated by forming CH4 hydrate in the pore spaces of glass beads, and its electrical properties were examined. Finally, changes in electrical resistivity were used to interpret CH4 recovery yields, while the guest composition of the gas hydrate was simultaneously analyzed by gas chromatography.