Environmental Challenges on Hydraulic Fracturing Stimulation in the Natural Gas Hydrate Reservoir: A Mini-Review

During the period of energy structure transformation for achieving carbon peak and carbon neutrality, it is an inevitable trend to search for a suitable energy source to replace traditional fossil energy. Natural gas hydrate (NGH) widely distributed in terrestrial permafrost and submarine areas has been considered to be a potential energy resource in recent decades. Among all the development techniques, hydraulic fracturing stimulation (HFS) stands out as one promising candidate for addressing the issues such as single-well low yield, small mining range, and short stable production time. Numerous studies have been reported to further improve the HFS efficiency in NGH reservoirs. Herein, to further enhance the efficiency of HFS techniques in NGH reservoirs, different aspects on the application of HFS, gas production behavior, properties of working fluids, and environmental issues caused by HFS have been comprehensively reviewed. The effect of the hydrate storage environment and reservoir type on the application of HFS was analyzed, indicating that HFS is more meaningful to Class 2/3 marine reservoirs. Meanwhile, the technical feasibility, characteristics, and production enhancement were discussed to provide an all-around view on the working principle of HFS, and it has been found that it is important to choose a suitable working fluid to ensure the stability and permeability of the artificial fractures. In addition, the interaction of working fluids with the NGH reservoir was discussed, showing that commonly working fluid formulation and the injection process would cause damage to the NGH reservoir. Finally, further developments are suggested to enhance the research on HFS in different reservoirs and the suitable working fluids, while the environmentally benign stimulation strategy of NGH is prospected.