• clathrates;
  • clays;
  • environmental chemistry;
  • hydrates;
  • methane


The direct recovery of methane from massive methane hydrates (MHs), artificial MH-bearing clays, and natural MH-bearing sediments is demonstrated, using either CO2 or a CO2/N2 gas mixture (20 mol % of CO2 and 80 mol % of N2, reproducing flue gas from a power plant) for methane replacement in complex marine systems. Natural gas hydrates (NGHs) can be converted into CO2 hydrate by a swapping mechanism. The overall process serves a dual purpose: it is a means of sustainable energy-source exploitation and greenhouse-gas sequestration. In particular, scant attention has been paid to the natural sediment clay portion in deep-sea gas hydrates, which is capable of storing a tremendous amount of NGH. The clay interlayer provides a unique chemical–physical environment for gas hydrates. Herein, for the first time, we pull out methane from intercalated methane hydrates in a clay interlayer using CO2 and a CO2/N2 gas mixture. The results of this study are expected to provide an essential physicochemical background required for large-scale NGH production under the seabed.