Enhancing Gas Production From Hydrate-Bearing Reservoirs Through Depressurization-Based Approaches: Knowledge From Laboratory Experiments

There have been several field tests around the world to recover natural gas from gas hydrate reservoirs. A most recent trial took place in the South China Sea, breaking the records of cumulative and daily gas yield from marine hydrate deposits. However, significant challenges still remain while approaching commercial gas production. These may involve but are not limited to the ultralow permeability of the reservoir, insufficient heat supply, unstable gas yield fluctuations, sand problem upon water production from the silty sediments, and secondary hydrate formation or ice generation blocking the pore spaces. Consequently, intensive efforts have been made to understand and, thereby, manipulate the complicated gas production process. Of special interest are the studies on the determination and optimization of the depressurization scheme, because depressurization is recognized to be most promising toward an economically efficient gas recovery. Therefore, in this work, we elaborated on the effects of pressure regulation on the behavior of gas and water yield and characteristics of the reservoir during the gas production process through depressurization-based approaches. Particular attention was paid on the enhancement of the gas production rate and energy efficiency under various scenarios. The advantages and limitations of the current investigation were also discussed to present preliminary suggestions and perspectives for future studies. This work could provide a brief view of the current efforts on improving the gas production efficiency at a laboratory scale; further investigations are still required to scale-up these findings to provide guidance to the field test in the future.