Experimental Study on Kinetic Behaviors of Natural Gas Hydrate Production via Continuous Simulated Seawater Injection

Natural gas hydrate (NGH) is a kind of potential energy with shallow buried depth, high energy density, huge reserves, and cleanliness. In this study, continuous seawater injection is adopted for NGH production experiments with applying a self-designed reactor which can simulate an NGH-bearing reservoir with a mini well, given that the surface seawater stores tremendous heat. Continuous seawater injection for NGH production can keep the balance between productivity and sand production through controlling production pressure with its thermodynamic and technical feasibilities. Kinetic behaviors of NGH production by continuous seawater injection are investigated using the simulated NGH-bearing reservoir. Meanwhile, the dissociation of NGH and its influence factors are analyzed. The threshold value of temperature for NGH dissociation is also discussed. The experimental results show that the changes in temperature and pressure keep constant at the initial stage of the continuous seawater injection process. However, temperature and pressure show obvious variation with injecting more seawater, which increase first and decrease subsequently. Especially, the methane production rate shows a high level after the temperature exceeded the threshold value for NGH dissociation. But the methane production rate drops quickly after a short period of high level and keeps a low level until the end of the experiment. The maximum value of the methane production rate and cumulative methane production become higher with the presence of a larger overheat and NGH saturation. The existence of a threshold value of the temperature for NGH dissociation is demonstrated by experimental works. Minimum threshold values of the temperature for NGH dissociation vary with the presence of different corresponding reservoir pressures.