Technical Paper: Benchmarking and Dynamic Simulation of Direct Electrical Heating (DEH) Operations in a Subsea Flowline

Society: OTC
Paper Number: 25754
Presentation Date: 2015
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Abstract

Direct electrical heating (DEH) was implemented on a 12-in, 13-km, subsea wet gas tieback flowline to assist in thermal and flow assurance management during startup and shutdown of production. The performance of the DEH system was critical for hydrate management in the single flowline configuration. However, it was very difficult to model the DEH system for the large-scale pipeline because of the constraints of computational speed. It was also difficult to determine the DEH performance because of the absence of temperature gauges within the DEH zone of the flowline. Based on the first available field data, the study was able to find a way to investigate the DEH performance using the pressure increase at the subsea template and riser top. A dynamic simulation model was then developed to match the DEH performance during both the heat-up process and heat-maintain process. This enabled further optimization of the operating procedures for the DEH system based on dynamic simulations run using the tuned and benchmarked thermohydraulic model.

The results showed that the DEH performance calculated from the pressure response was better than predicted during the design phase. The DEH heating process was well matched by the dynamic simulation in terms of pressure and temperature response in the flowline. The study demonstrated a novel way to determine the DEH performance for a subsea pipeline based on basic fluid dynamics theory. It demonstrated the applicability of dynamic thermohydraulic simulation tools in replicating the DEH process at the scale of the entire subsea flowline under both steady-state and transient operating conditions, which is important for the development of operating guidelines. The optimization of operating procedures with the dynamic simulation results reduced heat-up times (and thereby reduced production deferment) and minimized the hydrate formation risks during system shutdown and restart. An example was provided for future projects on how to use and optimize DEH operation to assist flow assurance management.

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