Advances and recommendations for multi-field characteristics and coupling seepage in natural gas hydrate development

As an unconventional, clean energy resource, natural gas hydrate is abundant and widely distributed in the subsea and permafrost area. Since the 1990s, permafrost and ocean hydrate production tests have been conducted successively by Canada, the United States, Japan and China. However, many problems such as the producing of sand, low gas production rate and very short stable production time of single well have been found during the production tests. The gas production rate was much less than the demand of the commercial exploitation. The main challenge is that the mechanism of hydrate dissociation, multi-phase, multi-component and multi-field coupling seepage characteristics in the process of hydrate exploitation still remain unclear. According to the multi-field coupling characteristics of hydraulic field, thermal field, chemical field and mechanical field involved in the development of natural gas hydrate, this paper summarizes the effects of hydrate formation/decomposition on the main characteristic parameters of each physical field, including the basic physical parameters of hydrate reservoirs and their dynamic evolution (porosity, hydrate saturation, permeability and relative permeability), thermodynamic parameters (thermal conductivity, specific heat, thermal diffusivity and heat of formation/decomposition of hydrate), kinetic characteristics of hydrate formation and decomposition, mechanical properties of pure hydrate and hydrate-bearing sediments. Finally, the multi-field coupling relationship and interaction in the seepage of natural gas hydrate development are reviewed, and suggestions for the future scientific research and technology development of multi-physics characteristics and coupling seepage in hydrate development are put forward. © 2020, Editorial Department of CJAM. All right reserved.