Natural Gas Hydrate (NGH) is a high combustion efficiency clean energy and its reserve is twice as that of natural gas and petroleum, so NGH is the potential resource which could overcome the increasing energy assumption. One of the essential aspects during the exploitation of NGH is to avoid risk, and here in this work, we summarized the relevant management experience to study the critical safety risk in the exploitation of natural gas hydrate. The problems that must be resolved during NGH exploitation were identified through the research on the comparison of the characteristics of conventional gas hydrate mining methods and potential drilling engineering risks and stratum damages in the processes of exploitation. Combined with typical case analysis of gas hydrate mining, it is concluded that the key for safe NGH exploitation is the changes of stratum stress caused by hydrate decomposition; and all safety management experiences should be based on steady drilling and reasonable exploitation to prevent environment, equipment, persons and other aspects damages from layering and stress changes.

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The electrical characteristics of fractured gas hydrate reservoirs were investigated through the diffusion-limited aggregation model, digital rock technology, and the finite element method. The results show that the fracture and gas hydrate have a significant effect on the electrical characteristics of rock partially saturated with gas hydrate, where the matrix pore and fracture mixed gas hydrate form a dual-porosity system. Due to the fracture and gas hydrate effect, the electrical characteristics of fractured gas hydrate reservoirs cannot be described well by traditional Archie equations. The resistivity index vs. water saturation curve of fractured gas hydrate reservoirs shows a nonlinear relationship for different gas hydrate pore habits (pore-filling, cementing, and grain-coating types), and this curve consists of two parts with different gas hydrate saturation exponents for pore-filling and cementing gas hydrate and presents a curve without a fixed water saturation exponent for grain-coating gas hydrate. Fractured gas hydrate reservoirs with different fracture apertures, different gas hydrate pore habits, and saturation features will lead to macroscopic electrical anisotropy. The results of theoretical analysis and numerical simulation show that the electrical anisotropy coefficient of fractured gas hydrate reservoirs is a function of gas hydrate saturation. The function curve consists of three segments with the turning point for pore-filling and cementing gas hydrate, and this curve can be divided into two parts through the turning point. The findings of this study can help for a better understanding of the electrical characteristics of fractured gas hydrate reservoirs, which have great significance for the exploration and development of gas hydrate resources.