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

Abstract

Abstract Direct Electrical Heating (DEH) was implemented on a 12" 13km subsea wet gas tieback flowline to assist in thermal and flow assurance management during start-up and shut-down 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 due to the constraints of computational speed. It was also difficult to determine the DEH performance due to 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 dynamic theory. It demonstrated the applicability of dynamic thermohydraulic simulation tools to replicate the DEH heating process at the scale of the entire subsea flow line under both steady state and transient operating conditions, which is important to the development of operating guidelines. The optimization of operating procedures with the dynamic simulation results resulted in 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.