A comprehensive review of in situ characterization, phase behavior, and predictive modeling of natural gas hydrates for sustainable energy development

Natural gas hydrates (NGHs) are widely regarded as a promising unconventional energy resource due to their high energy density and relatively low carbon emissions. However, their commercial development remains constrained by the low permeability and strong heterogeneity of hydrate-bearing sediments, complex multiphase flow behaviors, and dynamics phase transition during gas production. This study provides a comprehensive overview of recent advances in NGH research, with particular emphasis on in situ characterization, phase behavior, production technologies, and predictive modeling. We first summarize recent progress in in situ sampling and characterization techniques for evaluating hydrate occurrence, reservoir properties, and fluid distributions under geological conditions. These techniques are critical for capturing reservoir heterogeneity and improving the accuracy of resource assessment and modeling. Building on this foundation, we further examine the thermodynamics and kinetics of NGH. Furthermore, major production technologies, including depressurization, thermal stimulation, CO 2 –CH 4 replacement, and integrated production strategies, are critically evaluated with respect to their mechanisms, advantages, limitations, and engineering applicability. Recent progress in predictive modeling is also discussed, focusing on multiscale and multiphysics simulation frameworks that integrate thermal, hydrological, mechanical, and chemical processes to improve predictions of hydrate evolution and reservoir performance. Overall, this review identifies key scientific challenges and providing a roadmap for future research directions aimed at the sustainable and efficient exploitation of NGHs in the global energy transition.