Dissociation characteristics of methane hydrate using depressurization combined with thermal stimulation

Methane hydrate is considered as a potential energy source in the future due to its abundant reserves and high energy density. To investigate the influence of initial hydrate saturation, production pressure, and the temperature of thermal stimulation on gas production rate and cumulative gas production percentage, we conducted the methane hydrate dissociation experiments using depressurization, thermal stimulation and a combination of two methods in this study. It is found that when the gas production pressures are the same, the higher the hydrate initial saturation, the greater change in hydrate reservoir temperature. Therefore, it is easier to appear the phenomenon of icing and hydrate reformation when the hydrate saturation is higher. For example, the reservoir temperature dropped to below zero in depressurization process when the hydrate saturation was about 37%. However, the same phenomenon didn't appear as the saturation was about 12%. This may be due to more free gas in the reservoir with hydrate saturated of 37%. We also find that the temperature variation of reservoir can be reduced effectively by combination of depressurization and thermal stimulation method. And the average gas production rate is highest with combined method in the experiments. When the pressure of gas production is 2 MPa, compared with depressurization, the average of gas production can increase 54% when the combined method is used. The efficiency of gas production is very low when thermal stimulation was used alone. When the temperature of thermal stimulation is 11 °C, the average rate of gas production in the experiment of thermal stimulation is less than 1/3 of that in the experiment of the combined method.