Risk Prediction and Analysis of Hydrate Reformation in Drainage Pipeline for Gas Hydrate Production

In the process of marine gas hydrate exploitation, the decomposed gas and water of reservoir are easy to reform hydrate in the pipeline near the mud line, which causes serious flow guarantee risk. Due to the limited efficiency of gas-liquid separation in the production system, bubble flow can be formed in the drainage pipeline. Based on the continuity equation, momentum equation, temperature distribution equation, hydrate phase equilibrium model and hydrate formation rate model, the prediction model of hydrate reformation is established. The influences of the water production rate, ESP pressure on the temperature distribution, hydrate formation rate, hydrate volume fraction and multiphase flow pressure drop in the drainage pipeline were investigated. It is found that the increase of ESP pressure will magnify the hydrate formation region and the degree of subcooling, the increase of water production rate will increase the slurry flow rate in the drainage pipeline, which both lead to a significant rise in hydration formation rate and volume fraction. High ESP pressure and water production rate are the main source of safety risk of hydrate flow in the drainage pipeline. This study can provide a basis for the prediction of the hydrate reformation in the drainage pipeline during the production of marine gas hydrate, and lay a theoretical foundation for the efficient prevention and treatment of hydrate reformation.