Active heating systems have been successfully installed since 2007, culminating with the world's deepest "Direct Electrical Heating" (DEH) system in 1100m water depth installed in 2015 by a major offshore contractor. The company, with its market-leading track record in the design, fabrication and installation of pipe-in-pipe (PIP) solutions, is now collaborating on the qualification of the most efficient active heating technology – complementary to DEH systems – the "Electrically Heat Traced Flowline" (EHTF). This technology was originally introduced in 2000, and has undergone tests and improvements since 2009 within the framework of a cooperation between a major offshore contractor and a PiP design and manufacturing company.
The low power consumption EHTF Technology is based on a field-proven, high performance PiP system. A specific insulation material arrangement (mineral/silica based microporous pre-compressed insulation), combined with a reduced pressure environment, provides extremely competitive thermal performances, unmatched by other usual dry insulation materials. Heating is supplied via a combination of multiple bundles of three-phase low voltage wires, continuously laid all along the inner pipe (flowline) under the insulation.
The EHTF system provides the following advantages:
Low power heating requirements thanks to the thermal efficiency of the insulation system: typically in the order of kilowatts rather than megawatts for competing high-voltage systems;
High level of operational flexibility, reliability and redundancy thanks to the multiplicity of cables in the cross-section, which allows to face different heating level scenarios: both fluid preservation and permanent heating are envisaged during the operating field life.
This paper describes a typical EHTF system, and provides examples of applications to future project developments. An overview of vessel capabilities in safely installing EHTF systems (focusing on, but not limited to reeling) demonstrates that the EHTF is not only a competitive and suitable in-place solution compared to other systems available in the subsea market, but also a very effective solution from an operational point of view.
The current status of the EHTF qualification programme is also described. It includes the flowline components, the corresponding structures, termination modules and electrical connections to surface using wet-mateable connectors.
The paper also shows how the advantages of an EHTF system can improve the economics of field developments by providing significant modification of CAPEX ("SURF+SPS+Topside"), OPEX (less consumables, maintenance and intervention than classical preservation methods) and production (shorter start-up times and higher production turndown ratios allowed).
It opens up a whole range of new developments, by improving access to thermally demanding reserves, bringing flexibility and redundancy, and also allowing permanent heating and long tie-backs of up to 30km or more.
