To study the influence of hydrogen mixing ratio on the leakage of natural gas pipelines, a mathematical model for the leakage and diffusion of directly buried high?pressure hydrogen mixed natural gas pipelines was established based on computational fluid dynamics theory and numerical simulation method.The leakage status, volume fraction distribution of hydrogen mixed gas,and the distribution of soil pressure and gas velocity around the pipeline were analyzed under different hydrogen mixing ratios.The results show that with the increase of hydrogen mixing ratio, the explosion radius of hydrogen mixed gas in the atmosphere will gradually decrease,and the range of high?pressure area around the pipeline will gradually decrease,and the gas flow rate at the leakage port will gradually increase.When the hydrogen mixing ratio is 30%,the explosion radius in the atmosphere is reduced by 43%,and the gas flow rate at the leakage port is increased by 68%.This provides a theoretical reference for the safety and emergency repair of hydrogen?doped natural gas pipelines and has important practical significance for promoting the large?scale application of hydrogen?doped natural gas.

In the multiphase flow pipeline transportation system， in the process of hydrate slurry flow， rugged terrain will be encountered. At this time， the use of inclined pipeline is particularly important. Therefore， the influence of the flow characteristics of gas hydrate slurry in the inclined pipe on the blocked pipeline was studied. The hydrate plugging experiment of oil + natural gas in oil?based system was carried out on the low?temperature and high?pressure visual hydrate experimental loop， and the effects of initial pressure， initial flow and other factors on the flow and plugging time of natural gas hydrate slurry were explored. At the same time， the micro changes of hydrate particles in the process of hydrate formation， flow and pipe plugging were analyzed by real?time online particle tester. The experimental results show that with the increase of initial pressure， the induction time， formation time and slurry flow time of natural gas hydrate are shortened， and the pipe plugging trend of natural gas hydrate increases. With the increase of initial flow rate， the induction time， formation time and slurry flow time of natural gas hydrate are prolonged， and the pipe plugging trend of natural gas hydrate is reduced. Finally， the process from hydrate formation to pipe plugging and the plugging mechanism were analyzed. The research results of gas hydrate plugging pipelines in oil?based systems show that the probability of gas hydrates blocking pipelines can be effectively reduced by reducing initial pressure and increasing initial flow rates in oil?based systems. The research results can provide theoretical reference and basis for maintaining and ensuring the safe flow of natural gas hydrate in pipelines.