1-Dimensional Productivity Evaluation for Methane Hydrate Replacement Using Carbon Dioxide and Nitrogen

Based on the replacement of CH₄ with CO₂ + N₂ (also called "swapping"), we demonstrated the direct recovery of methane from artificially synthetic methane hydrate sediments. The injection of CO₂ + N₂ existing as a gaseous state at deep-sea conditions of high pressure and low temperature makes the favorable diffusion and high methane recovery compared with pure CO₂ injection. For simulation of actual deep-sea MH sediments, we first attempted to explore the replacement of CH4 with CO₂+ N₂ gas in the macroscopic scale under natural MH reservoir condition and thus designed and set up the 1-dimensional high-pressure reactor with around 10m length. Natural MH can be converted into CO₂ hydrate, potentially carrying out both energy resource supply and CO₂ sequestration. In particular, the fluid movement under continuous gas injection is described along with actual replacement efficiency according to several gas movement velocities. We clearly confirmed that the replacement efficiency is inversely proportional to the injection rate of CO₂ + N₂ gas mixture that is directly related with the contact time. From the analysis on compositional profiles at each port, the length is required more than 5.6 m to have noticeable recovery rate for natural gas hydrate production. For future off-shore field tests, we should establish the optimized MH production process with careful consideration of various influencing variables.