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.

Active heating technologies are for the moment based on topsides power distribution, limiting by default, the length of the flowline that can be heated. It is proposed to extend the range of active heating technologies by utilizing a field architecture that enables production for very long tie-backs by combining subsea electrical power distribution with the most efficient active heating technology the "Electrically Heat Traced Flowline" (EHTF) technology. The paper will present typical field architectures that require such combinations of subsea electrical power distribution and efficient active heating technology, typically brown fields with remote tie-backs that could not be developed with available technologies. EHTF Technology is based on a field proven high performance thermally insulated pipe-in-pipe, limiting the heat loss. Multiple high voltage wires, connected as three phase circuits, laid under the insulation along the entire length of the fluid carrier pipe, are used to provide heating. The heating wires extend typically 20km each side of a small in-line structure allowing safe penetrations into the pipe-in- pipe annulus. This small structure is powered on by a power cable, laid alongside the flowline, via a subsea electrical power distribution unit, which can be combined with a subsea transformer, to distribute the power to the multiple heating circuits within the annulus. Exceptional thermal efficiency of the insulation system generates lower heating power requirements, meaning that subsea distribution systems can be designed with reliable and off the shelf components, easily retrievable and maintained with low operational expenditures. Multiple circuits in the cross-section offer a greater operational flexibility and improved reliability of the system. Different power outputs can be provided from simple switching control depending on the heating requirement. Combining an efficient, reliable and flexible active heating technology with a simple and robust subsea power distribution allows development of remote fields that can be tied-back to existing facilities, virtually without limitation in length.

Standard field architecture is generally based on topsides production and distribution of power and chemicals necessary to operate equipment in drill centers. The paper will present efficient field architectures adapted to operate remote tie-backs with different combinations of subsea electrical power distribution, remote power generation and storage, and improved ways to mitigate corrosion, hydrates and wax issues for long tie-backs. Developing remote resources requires several technology bricks that enable a cost effective and reliable technical solution. To reduce the CAPEX, the main objective is to reduce the number of tubes typically with one single heated flowline to avoid a long and costly service line or with one small power cable and local distribution of power to avoid a heavy and expensive large umbilical. Alternatively, power can be generated and stored at drill center location and chemicals can also be managed locally with limited OPEX. A significant focus was done recently on technology developments enabling long distance tie-back developments. Domain of application and interest of each technology is generally well known and the delivered value is well presented. Looking for the most appropriate combination of technologies on a new field development is now the new challenge to figure out new opportunities. This paper proposes to group the long distance tie-backs fields in three main categories based on extensive studies done for several operators and to present the best architecture for each category. The first category groups very long distance single end tie-backs for which a cold flow system combined with full electrical equipment at drill center location is adapted. The second one is applicable for more consequent development where several drill centers are combined to one long and heated export line; with subsea electrical distribution to power each branch of the remote field and local management of chemicals at each drill center. The third category groups all daisy chain developments for which a heated line gathers the production coming from each fully electrical drill center. Each field development can generally be categorized in one out of the three categories presented in this paper. Based on this categorization, the right combination of low carbon and reliable new technologies enables valuable development of long tie-backs and then increases utilization area of each existing asset.

The paper discusses integrated all-electric solutions (iAES) that offer significant optimisation of field architecture and enhanced viability of both greenfield and brownfield developments. The discussion will be on field optimisations related to power and subsea chemical distribution to fully enhance the subsea electric field of the future. Conventional subsea field developments rely on electrohydraulic architectures to distribute chemicals, power, control, and communications from the host to the drill centres. The multiplication of tiebacks and their distance to a single host, as well as the increasing depths of subsea development, provide opportunities for a change in the technologies used subsea today, to improve the overall project economics. Yet the pace of change in technologies and field architectures remains slow. Over the last two decades, major improvements have been made in the development and qualification of subsea electrical equipment. The track record of the equipment installed on the seabed is now significant, although all-electric architecture has not become the new standard yet. The main advantages of an iAES lie in the simplification of subsea architecture and the reduction in the number of components. This lighter design allows a reduction of capital expenditures (CAPEX) and operational expenditures (OPEX), as well as shorter project delivery times and installation campaigns. The energy efficiency is also greatly improved, leading to a reduction in greenhouse gas emissions. The iAES is an enabler toward the energy transition, facilitating the integration of renewable sources into power subsea equipment. This paper will introduce the iAES and show how it offers significantly optimised field architecture and enhances viability of both greenfield and brownfield projects. It will provide the all-electric technology building blocks for subsea structures and will also explain how to optimise power in the field and in subsea chemical distribution to fully enhance the subsea electric field of the future. And it will include an outline of integrated control concepts for subsea production systems, boosting systems, and the subsea chemical storage and injection skids.

The design of a long gas flowline laid on a rough seabed and in which HP/HT gas is circulating shows that the numerous spans along the line were all acceptable and that some acceptable lateral buckles will occur at some key features (crests). A long section of the line was expected to be anchored preventing any walking. A first analysis with the steepest P/T transients showed no walking behaviour of the line. However it was observed that, when the line is gradually heated to the highest HT/HP profiles, unacceptable walking is observed at hot end. This paper will present how this line was designed and how an effective mitigation design was performed to prevent unacceptable walking and how that was implemented at the appropriate time in the overall design process. Design activities were performed with non-linear finite-element software able to model the pipeline and its interaction with the rough seabed. The standard design activities were done, specifically; on-bottom roughness, lateral buckling analyses and their conclusions combined at the end of the design process into a global model built to simulate potential interaction between buckles and spans. This is a stepped process that should be followed in any pipeline design activities. All spans and all potential rogue buckles were found acceptable, and the steepest HP/HT transients did not induce walking behaviour, as per conclusions from preliminary engineering studies. However, combining the most severe HP/HT scenario (corresponding to restart of the wells one after another) found spans along the line and the most probable scenario for locations of buckles led to unacceptable walking at hot end. This phenomenon is explained by the interaction between buckles and spans, as they evolve with the applied loadings. Mitigating this walking was achieved by integrating a padeye in the end structure. This particular padeye was linked by a chain to a single suction pile installed nearby. The integration of the mitigating padeye was done without any interruption to the overall schedule. This was achieved by an effective design process which listed the Key Interface Datas (KIDs) which in turn defines the important milestones between engineering disciplines (pipeline, structure, installation, fabrication). There is no one single scenario that can lead to pipeline walking, particularly for lines laid on rough seabed with many spans and buckles. It is recommended to always study a case where several cycles of maximum operational profiles are applied. The overall design process should also list the Key Interface Datas in the overall schedule in order to ease the interfaces between engineering disciplines.