Technip developed the Electrically Trace Heated Pipe in Pipe (ETH-PiP) technology to overcome some of the challenges associated with deeper and remote offshore oil and gas production. This active heating technology applies power to achieve a production fluid temperature above the hydrate equilibrium or wax appearance temperatures either continuously, during normal production, or intermittently, during shutdown periods. In the unlikely event of hydrate plugging of production lines, active heating can be used for remediation.

The objective of this work was to demonstrate that a long, non-permeable hydrate plug can be dissociated in a safe and controlled manner with the ETH-PiP technology. Technip through a JIP program that started in 2012 at the IFPEN facilities at Lyon with Total E&P, ExxonMobil Development Company and Woodside Energy Ltd. have been investigating hydrate dissociation in heated flow lines and studying the associated risks of local pressure build-up and plug run-away.

A 6 " OD and 18 m long ETH-PiP prototype was manufactured and connected to the Lyre loop. It was equipped with sensors for accurately monitoring the dissociation process. A first experimental campaign was focused on studying different dissociation heating strategies. A second experimental campaign, presented in this paper, studied hydrate plug dissociation under severe conditions: dissociation in a closed volume; dissociation under high differential pressure; dissociation with unbalanced heating; and dissociation in presence of viscous oil.

This paper summarizes the experimental procedures and presents some findings of the second experimental campaign. Massive hydrate plugs of up to 200 kg were formed with high water to hydrate conversion rates. The plugs were characterized under differential pressures of up to 35 bar. The characterizations revealed that pressure communication across hydrate plugs was strongly affected by the presence of free water or oil inside the plug porous structure. Among the dissociation strategies, the dissociation in a closed volume was studied and the pressure management under these conditions was tested.

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