Hydrate Management in Deadlegs: Effect of Wall Temperature on Hydrate Deposition

Deadlegs in oil and gas production systems are pipe sections with no through flow. They are often connected to a hot header but exposed to a cold environment. Deadlegs face hydrate challenges, as water condensation on the cold pipe wall can lead to continuous hydrate deposition. The water condensation and hydrate deposition are strongly influenced by temperature. The temperature boundary conditions of a deadleg consist of the header and the wall temperature and both affect the temperature field and the hydrate deposition process. This study focuses on the effects of the wall temperature on hydrate deposition in a 2-in.-ID gas-filled vertical deadleg at constant header temperature. The wall temperatures considered are 4, 10, and 15 degrees C, with header temperatures at 30 and 80 degrees C. All the experiments are conducted with a methane/ethane (75/25 mol %) gas mixture (sII hydrate) at a constant pressure of 100 bar. The hydrate equilibrium temperature is 18.9 degrees C from the prediction tool (CSMGem). The results show that a high wall temperature leads to a warm environment which subsequently reduces the hydrate deposit growth rate and delays the eventual plugging of the deadleg. However, the results also suggest that a high wall temperature may not eliminate the possibility of forming a plug as long as the conditions in the deadleg are lower than the hydrate equilibrium temperature. Moreover, the wall temperature seems to have a small impact on the potential hydrate plug location. The results of this study provide further understanding of the wall temperature in the hydrate deposition mechanism in deadlegs.