Kinetics Decomposition Characteristics of Natural Gas Hydrate Under Combined Chemical Injection and Depressurization in Pipeline Deposits

The decomposition characteristics of natural gas hydrate in pipeline deposits are the critical factor affecting the safe operation of long-distance natural gas pipelines. To clarify the kinetic decomposition patterns of hydrate deposits under different conditions, this work focused on the combined decomposition method of depressurization and chemical injection. It investigated the effect of polyvinylpyrrolidone (PVP) on the kinetic parameters of hydrate decomposition, including kinetic decomposition characteristics, hydrate decomposition rate, and gas production. The results indicated that hydrate exhibited differences between the overall disintegration of the pure water system and the local expansion decomposition of the PVP system during the decomposition stage of chemical injection. During the depressurization decomposition stage, the rapid decomposition rate was shown in the pure water system, while a slowed decomposition rate was shown in the PVP system. During the chemical injection decomposition stage, the decomposition rate was accelerated, and the initial gas production rate was enhanced in the 0.1 wt% PVP system. Compared to the pure water system, the hydrate decomposition rate was increased by 21.57%. Furthermore, the presence of PVP helped mitigate secondary formation during depressurization decomposition, thereby enhancing the stability of hydrate decomposition. During the depressurization decomposition stage, compared to the pure water system, the hydrate decomposition rate was reduced by 44.02%, and the gas production was decreased by 22.71% because of the presence of PVP. The findings not only provided new experimental evidence for understanding the decomposition mechanism of natural gas hydrate but also had engineering significance for the measures to unclog pipelines and ensure the flow of oil and gas in offshore energy extraction.