Electrically Traced Heated Pipe in Pipe (ETH-PiP) technology has been developed to overcome some of the challenges associated with deeper and more remote offshore oil and gas production. This active heating technology applies power to achieve a production fluid temperature above the wax or hydrate appearance temperature either continuously, during normal production, or intermittently, during shutdown periods. Concerning hydrate management, the contractor Company in collaboration with Major Operators conducting experimental and modelling studies to investigate hydrate dissociation in heated flowlines through a Joint Industry Project (JIP) kicked-off in 2012. The main objective of these investigations is to demonstrate that a long, non-permeable hydrate plug can be dissociated in a safe and controlled manner with the ETH-PiP technology. Large hydrate plugs (approximately 200 kg each) are formed in an 18m ETH-PiP 6? OD prototype, using a water and gas system equipped with DTS fiber optics systems for temperature monitoring, pressure and temperature sensors, and high accuracy gas flow meters. Different heating strategies are tested to investigate the best active heating procedure for safe hydrate plug dissociation, using temperature, pressure and released gas flow rate monitoring along the entire length of the prototype. Hydrate plug dissociations are performed in open or closed volumes for various conditions during the 2nd phase of the experimental campaign, which started at the end of 2013. High pressure differentials are applied across the hydrate plugs; non-uniform longitudinal heating profiles are applied to reproduce operating conditions similar to direct electrical heating; and three-phase dissociation experiments are conducted to simulate the influence of oil present in the hydrate pores on the plug dissociation. The paper gives an overview of the experimental set-up and measuring techniques used. It describes the hydrate plug formation, location, and characterization, as well as the successful dissociation of hydrate plugs. Preliminary simulation results based on a specifically developed "in-house" simulator are presented, as well as extrapolation of the results to real subsea conditions. This test program demonstrated that large non-permeable hydrate blockages in single line field architectures could be dissociated without local pressure build-up or plug run-away using ETH-PiP technology.

With most of the world’s largest and easiest-to-exploit deepwater oil reservoirs already under development or producing, the industry is now facing new deep offshore challenges: the production of smaller fields that often contain more difficult oils. The tie-back of new fields to existing facilities can be a viable method for developing such marginal offshore fields, which are often too small to be developed economically on their own. The use of subsea processing and innovative field architectures as development solutions is fast becoming a reality. Such challenges are already being addressed in the development of certain fields in the Gulf of Mexico (King, Perdido...), Brazil (Marlim, BC-10...) and the Gulf of Guinea (Pazflor). However, long subsea tie-backs come with inherent complications. The most demanding are the flow assurance issues arising from the different operating regimes, and these may be combined with more viscous fluids and/or reservoirs at low pressure or low temperature. This paper examines the advantages and limitations of various field architectures that may be considered for long satellite tie-back lengths in deep waters. The first part addresses production considerations such as turndown, preservation and restart management for each candidate architecture. The impact of tie-back length on operating modes is also evaluated. The second part examines the impact of these operating modes on the receiving facilities.

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.