Hydrate Management in Deadlegs: Hydrate Deposition in Pipes with Complex Geometry

Abstract

Deadlegs are pipe sections with no through flow for maintenance services in oil/gas production and transportation systems. As deadlegs are filled with stagnant fluids, the pipe wall is typically colder than the main flowlines. Water vapor can condense on the wall and form hydrates. The resulting hydrate deposits in the deadleg can pose significant operational risks. Hydrate deposition in gas environment has been studied for many different parameters. However, hydrate deposition in pipes with complex geometry, which is common in oil/gas pipeline networks, has not been considered yet. In this study, we investigate hydrate deposition in the 180° straight pipe and the 90° bent pipe with varying tilt angles. While a natural convection in the 180° straight pipe results can be considerable, it becomes less significant in the horizontal piece of the 90° bent pipe. When tilting this pipe in the negative angle, the temperature gradient along the pipe changed pronouncedly and condensed water droplets dripped down to the end of the pipe, leading to the accumulation of wet hydrate deposits. In the tilted 90° bent pipe with positive angles, free water in deposits, which is not yet converted into hydrates, dripped back to the header through which warm water vapor was initially introduced to the cold pipe. The resulting hydrate deposits were dry and spread out along the pipe surface, similar to the 180° straight pipe case. Our experimental results demonstrate that hydrate deposition in deadlegs can be largely affected by the pipe geometry.