Heat and mass transfer analysis during the process of methane hydrate dissociation by thermal stimulation

Natural Gas Hydrate (NGH) is characterized by large reserves and cleanliness, which has attracted wide attention around the world. Thermal stimulation is considered to be one of the possible methods to facilitate hydrate dissociation. In this paper, the hydrate is dissociated through injecting hot water. In order to reveal the influence of the speed and the temperature of injected hot water on the temperature distribution, hydrate dissociation front, gas production rate, and cumulative gas production, a 2D cylindrical mathematical model of thermally-induced hydrate dissociation was established. The results show that the dissociation process can be regarded as a moving boundary ablation process. The dissociation front divides the whole reservoir into three sections: complete dissociation section, ongoing dissociation section, and undissociated section, and the range of ongoing dissociation section is a very narrow area characterized by a relatively intensive temperature contour, which indicates that the temperature drops rapidly during the hydrate dissociation. The temperature at the dissociation front is almost constant under different hot water injection speeds or temperatures. The injection speed and the temperature of hot water seem to have similar effects on hydrate dissociation. The enhanced hot water injection speed or hot water injection temperature will result in a faster gas production rate, a quicker movement of the dissociation front, and a shorter duration time of gas production, however, hot water injection speed and temperature have little impact on the final gas production. The results may provide a guidance for safely and efficiently exploiting NGH.