Research progress on accumulation characteristics of different types of hydrates

In recent years, the study of reservoir-forming characteristics in different types of gas hydrates has garnered significant attention. The occurrence type of hydrates exerts an important influence on reservoir properties and developments. This paper presents a comprehensive analysis of the distribution, accumulation, and stability conditions of natural gas hydrates. We delve into the characteristics of gas sources, gas migration channels, reservoir conditions, structural environments, and reservoir-forming models. Furthermore, we analyze the specific differences between pore-filling and fracture-filling hydrates in these aspects. Our findings show that favorable reservoir conditions for pore-filling hydrates include suitable pore structure, adequate permeability, and high gas content. Fracture-filling hydrates are mainly distributed in submarine fractures and are closely related to geological structures. The composition of the sediment matrix, fracture occurrence, and geological structure collectively determine the formation type of hydrates. Compared with pore-filling hydrates, fracture-filling hydrates are significantly influenced by geological structures such as fractures and faults in terms of reservoir formation mode. In the future, we suggest focusing on the differences between pore-filling and fracture-filling hydrates in the formation process, occurrence form, and physical responses. By integrating experimental and numerical simulation methods, we propose innovating reservoir identification techniques from multi-disciplinary and cross-scale perspectives. This will enhance our understanding of reservoir formation differences and provide a scientific basis for the efficient development of hydrate resources. © 2024 Geological Society of China. All rights reserved.