Parameter optimization for natural gas hydrate solid fluidization

The marine shallow gas hydrate reservoirs consist mainly of non-diagenetic hydrates, characterized by shallow burial, weak cementation, loose mineral deposition, and fragility. By non-diagenetic, we mean hydrates that have not undergone significant post-depositional chemical or physical alteration processes, unlike diagenetic hydrates, which form through chemical and structural changes in sediments after their deposition. Conventional extraction methods for non-diagenetic hydrates often lead to uncontrollable and unsafe issues, such as gas collection challenges and leakage risks. To address these, this paper presents a gas-liquid-solid multiphase non-isothermal transient flow model incorporating hydrate phase transitions for the solid fluidization exploitation method. The model couples multiphase flow, heat, and mass transfer in the wellbore with a dynamic decomposition model for hydrate-bearing particles. An optimization method for key parameters in hydrate solid fluidization is also proposed. The results show that the critical depth of hydrate decomposition increases over time, with a rising gas phase volume fraction. Increasing mining rate, seawater temperature, and salinity accelerates decomposition, while adjusting wellhead pressure controls the decomposition depth. Higher mining rates, seawater temperature, and salinity enhance gas production, while greater wellhead pressure and larger wellbore diameters boost solid production. These findings provide key insights for the safe and efficient transport of hydrate-bearing particles and advancing solid fluidization technology.