Flow assurance modeling using an Electrical Trace Heated Pipe-In-Pipe: From Qualification to Offshore Testing

Abstract

The use of subsea technologies and innovative field architectures as development solutions is fast becoming a reality. Thermal management is a key issue and using electrical heating such as the Electrical Trace Heated Pipe-in-Pipe (ETH-PIP) can be considered as an alternative to fluid circulation or chemical injection for preservation purposes. The ETH-PIP is a standard Pipe-in-Pipe enhanced with 4 heat trace cables, and 2 DTS optical fibers spiralled against the inner pipe and covered by a high performance thermal insulation. As part of TOTAL qualification for the ISLAY project, the world first field development using subsea ETH-PIP technology, significant efforts have been put on the development and validation of flow assurance models able to predict the interaction of the active heating system with hydrocarbon mixtures during production, shut-down and restart. This paper reviews and describes the development of the necessary models required to perform the thermal design and the flow assurance calculations all the way to the elaboration of a control system for monitoring the subsea operations. The focus has initially been put on the elaboration of a CFD model able to fully capture the local thermal behavior of every component. Finally, a simplified model describing the ETH-PIP thermal behavior is introduced into a multiphase flow simulator (Olga or Leda) to perform the necessary flow assurance calculations predicting the production fluid behavior during the transient active heating operations. This paper also assesses the validation of the models. During the TOTAL qualification process, a 12m test rig has been set up for the validation of the the U value, cooldown and warm-up predictions coming from the CFD and Multiphase flow models. A larger scale validation has been performed comparing the fiber optics measurements to the model predictions during the commissioning test after installation. As an ultimate validation step, a complete offshore test has been realized during the Islay September 2012 shut-in period, where a series of warm-up, temperature maintainance and cooldown took place and successfuly compared to the models. The elaboration and the validation of the ETH-PIP flow assurance model using CFD and Multiphase flow simulations enable the design and the prediction of the production fluid behavior during any operating scenarios. The developed models also open the door to the elaboration of a live monitoring system of the flowline thermal behavior which fully enables the ETH-PIP system operability for offshore operations.