Progress and challenges on gas production from natural gas hydrate-bearing sediment

Natural gas hydrate (NGH) is widely distributed in permafrost and submarine areas. It has been considered as a potential energy resource in the future since its reserves are estimated two times more than those of the conventional fossil energy. Production from NGH reservoirs with economical methods is critical to realize energy application of NGH. Series of NGH exploitation methods such as depressurization, thermal stimulation, chemical inhibitor injection, and replacement method have been proposed and widely studied by experiments and numerical methods, and several field trials have also been conducted. Producing gas from NGH reservoir is a complex process with coupling of thermal/hydraulic/chemical/mechanical (THCM), which leads to NGH exploitation more different than that of traditional fossil resources. And none of these methods can be applied for long-term commercial NGH exploitation. This paper has reviewed all the developed exploitation methods with comments of advantages and limitations. The challenges of gas production from hydrate-bearing sediments are also summarized. Besides, some possible solutions for these challenges including reservoir restoration with formation of CO2 hydrate, improving replacement rate of CO2 with supercritical CO2 jetting technique. Furthermore, electrical heating of hydrate-bearing sediments with persistent currents or high voltage pulse discharge is put forward.