Abstract: To determine the displacement dynamics constant of mixed gas ( CO₂ + N₂ ) injected during the process of natural gas hydrate development, research methods such as indoor experiments and chemical thermodynamic calculations were used. Under the conditions of displacement temperature of 274.15 K and displacement pressure of 3.7 MPa, the driving force, displacement rate and hydrate displacement rate constant during the displacement of natural gas hydrates by 3 groups of mixed gases were studied. And the hydrate displacement dynamics constant was obtained based on inversion of displacement dynamics models. The results show that during the hydrate displacement process, the displacement driving force of the mixed gas ( CO₂ + N₂) and the hydrate displacement rate decrease rapidly with the increase of the displacement time. The generation dynamics constants of CO₂ hydrate in the 3 groups of experiments are relatively close, with an average value of 0.025 2 mol/( h·m²·MPa ), and the degradation dynamics constant of CH₄ hydrate are also relatively close, with an average value of 0.0316 mol/( h·m²·MPa ). Under the same conditions of hydrate system, the dynamics constant of hydrate displacement is only related to the temperature and pressure. The research results have important guiding significance for the dynamic prediction of natural gas hydrate development by using mixed gas (CO₂ + N₂) displacement.

Key words: gas hydrate, mixed gas, displacement, dynamics, fugacity difference