Experimental study on influencing factors for hydrate dissociation in a hot brine injection process

Key words:  natural gas hydrate  hot brine injection  hydrate dissociation  energy efficiency

Abstract:

The formation and dissociation of natural gas hydrate (NGH) was studied using a specially designed one-dimensional experimental set-up to simulate the hydrate bearing sediment below the seabed. NGH was formed in a sandpack model (with a diameter of 8cm and lengh of 80cm), and then hot brine was injected into the sandpack to dissociate the gas hydrate. The important factors that influencing the energy efficiency for hydrate dissociation were investigated, including the temperature of the injected hot brine, the saturation and initial temperature of hydrate formed, and the injection time and rate of the hot brine. The energy efficiency was defined as the ratio of the heat of the methane gas released to the injection heat. The experimental results show that, the order from big to small of factors that influencing the energy efficiency for hydrate dissociation is temperature of the injected hot brine, the saturation, initial temperature, the injection time and rate of the hot brine. The higher hydrate saturation and initial temperature, the higher energy efficiency, while the higher the hot-brine temperature, the lower the energy efficiency. The temperature, injection time and injection rate of hot-brine can be optimized in order to achieve a high thermal efficiency in the process of the hydrate dissociation. Under the experimental conditions, a maximum energy efficiency of 6.74is achieved during the dissociation of hydrate formed at 5℃ with a saturation of 48%, when hot-brine of 40℃ is injected at a rate of 12mL/min for 350min.