The experimental testing and analysis of strength and deformation characteristics of hydrate reservoirs is an integral part of natural gas hydrate exploitation. However, studies so far have failed to deeply explore samples from the South China Sea. Especially, there is a lack of a simple and applicable method to estimate their mechanical behaviors. Thus, based on test data, an improved Duncan-Chang model is established in this paper to characterize the strength and deformation of reconstituted samples with various hydrate saturation and stress states from this area. This model can accurately describe the strain-hardening characteristics, and failure strength is estimated by the improved Drucker-Prager criterion with high fitting accuracy. The initial elastic modulus and failure ratio are given by the proposed empirical models, which are obtained from experimental data and fitting methods. Generally, this model has several advantages including simple structure, favorable performances, and a limited number of model parameters. Therefore, it could be widely used in strength and deformation analysis. This study can support the prevention and control of geological risks during natural gas hydrate exploitation in the South China Sea.

As a promising substitute for conventional fossil fuels with huge reserves, clayey-silt natural gas hydrate has been proved to be widely distributed in the continental margins of the marine environment. Characterization and development of this kind of natural gas hydrate reservoirs face unique challenges, compared with that of natural gas hydrate in marine sandy sediments. This review summarizes the basic methods for natural gas hydrate reservoir characterization and development, and discusses the applicability of these methods in marine clayey-silt natural gas hydrate reservoirs. Feasibilities of classical oil and gas reservoir characterization methods and models applied to hydrate-bearing strata remain elusive, let alone clayey-silt hydrate deposits. Current natural gas hydrate development methods are restricted by low gas productivity, potential geomechanical instability, and extremely high costs. Economically feasible technologies considering the influences of geotechnical issues are needed for the commercialization of natural gas hydrate contained in clayey-silt sediment.