Hydrate Management in Deadlegs: Effect of Pipe Size on Hydrate Deposition

Deadlegs are defined as pipe sections in intermittent use for production or special services in oil/gas production systems. Due to the absence of flow, deadlegs are commonly much colder than the main flowlines or the process equipment to which they are connected. Therefore, water vapor tends to condense on the pipe wall of deadlegs, resulting in a potential risk for hydrate deposition. Over time the deadleg may be blocked completely by hydrates. Proper management of hydrates in deadlegs is critical, for both economical and safety reasons. To better address the remediation strategies in design and operation to mitigate the formation of hydrate deposits in vertical deadleg systems, we established an experimental protocol with gas-filled vertical deadlegs of various ratios of length over inner diameter (Lpipe/ID). The pipes have inner diameters of 2, 3, or 4 in. Each pipe system has five temperature-controlled sections. Water is supplied from the header at the bottom dominantly by natural convection. Experiments in each of the systems provide quantitative results for the center temperature profile, the hydrate growth in the top section through visual observation, the amount of water recovered, and the hydrate deposit distribution (inspected via borescope). On the basis of the results, we discuss the effects of inner diameter (ID), pipe length (Lpipe), and Lpipe/ID. The results also show a possibility of scaling results (the hydrate deposit distribution and plug position) over the pipe size by using the characteristic length Lpipe/ID.