Analyzing the Process of Gas Production from Methane Hydrate via Nitrogen Injection

The application of air or nitrogen injection to extract natural gas from hydrates has attracted considerable attention because air and nitrogen are abundant; however, few studies have considered the relatively new method. This study employed magnetic resonance imaging to investigate the characteristics of hydrate dissociation via N-2 injection. The results show that methane hydrate dissociation using N-2 injection can be divided into three main stages: free gas and water liberation, hydrate dissociation driven by chemical potential differences, and restriction of hydrate dissociation due to increased resistance to N-2 diffusion and a decreased contact area between N-2 and hydrate. Various factors associated with the N-2 injection method were considered, including injection rate and hydrate saturation. Furthermore, a comparison of recovery injection ratio and methane cumulative production ratio to the results of hydrate dissociation via depressurization suggests that during low-hydrate saturation exploitation, N-2 injection has advantages over the depressurization method.