Prediction model and risk analysis of hydrate deposition and blockage in reduced-diameter pipelines

In deep-water gas production and transportation, reduced-diameter structures are used extensively for connecting pipeline. The flow distribution is more complex and the processes of hydrate formation, migration, and deposition are yet to be characterized compared with the conventional pipelines. A new hydrate formation model in a reduced-diameter pipe is developed that considers the throttling effect and uneven thickness distributions of the liquid film on the wall. By solving the deposition velocities of hydrate particles inside and outside of low-speed eddy zones and considering the shedding process of the hydrate layer, the thickness of the deposition layer and blockage time can be accurately predicted. The results suggest that the radial growth rate attains the maximum value at the pipe shrinkage, which is thusly determined to be a high-risk area for hydrate blockage. The temperature decreased rapidly along the pipelines and attained its lowest value in the reduced-diameter region. Parameters such as the mass flow rate of the droplet and film, rate of hydrate formation, and hydrate distribution were highly correlated with the thickness distribution of the hydrate layer. The study establishes a theoretical basis for the prediction and prevention of hydrate risk during gas transportation in pipelines involving complex structures.