Hydrate Formation and Blockage in Inlet/Outlet and Slope Pipes of Gas–Water–Oil Transportation Pipeline

Hydrate blockage always imposes a common problem in oil and natural gas transportation pipelines. The blockage usually occurs at special locations, such as the inlet and outlet of the pump or the slope sections, which are less likely to be detected and more likely to cause serious consequences. A novel fully visual flow loop was used to study the evolution of hydrate formation and blockage in different parts of the pipeline. The results showed that 50% water cut with low liquid loading has the fastest hydrate formation speed. Hydrate usually gathers in the inlet section with some fluid accumulating, which increases the local pressure drop. The hydrate volume fraction at the inlet is higher than at the outlet, and the difference value gradually increases with time and results in hydrate blockage at the inlet parts. Moreover, the results found the most prone location of hydrate blockage in the slope transition section. The rolling hydrate particles in the slug flow at the upslope will backflow due to the action of gravity. It will collide with the fluid and hydrate particles in the horizontal pipe at the junction of the upslope section. This phenomenon results in a negative pressure drop with hydrate blockage in the slope pipes. In addition, the use of an inhibitor (0.5% PVCap) can reduce the hydrate formation speed by more than seven times and the maximum water conversion rate by more than 30%, which can significantly reduce the risk of hydrate blockage.