Active heated pipe technologies are enabling solutions for field developments allowing cost effective management of flow assurance to overcome specific challenges like longer distance tie-backs and greater water depths. This paper introduces wax and hydrate issues and conventional approaches to manage them. It highlights the need for other approaches, such as active heating technologies, to reach longer tie-back distances and greater water depths. It reviews Direct Electrical Heating (DEH), Electrically Heat-Traced Flowline (EHTF), and active heated flowline bundles comprising Hot Water Circulation (HWC) and EHTF in bundle. A general presentation of these systems is given, including design, fabrication and installation methods, as well as the maturity of the technology. Typical field architecture is proposed to illustrate the benefits of each active heating technology in terms of field development optimisation. This paper provides global information and an understanding of different available solutions for active heating pipeline systems, with technical and economic perspectives, and concludes with elements for selection of optimised field architecture. Wet DEH is a field proven technology with large track record that has already been installed on a 43km pipeline in 1070m water depth. It fits production fields not requiring high thermal insulation performances and thus allowing wet insulated pipe (U-Value =2W/m2.K). The system presents high electrical power requirement (50-150W/m). Therefore, infrastructure capacities in terms of footprint and power supply available have to be checked against specific project power requirements. EHTF fits production fields requiring high thermal insulation performance provided by Pipe-in-pipe (down to U-Value < 0.5W/m2.K). Thanks to its high efficiency, the system has low power requirement (typically below 50W/m). Therefore, it can also be an alternative to DEH when topsides capacities cannot meet footprint and power supply requirements. Pipeline heat tracing is a known technology for onshore plants and by extension applicable for subsea applications. The implementation of EHTF is completing qualification of this technology for deepwater applications. HWC within bundle is a field proven technology. It fits production fields requiring high thermal insulation performance provided by bundle arrangement (down to U-Value < 0.5W/m2.K). The technology requires power and equipment to heat water thus impacting topsides space. These requirements vary considering project specific needs and selection of direct or indirect heating. For example, re-use of the produced water as an indirect heating medium can highly limit required power generation.

Development of thermal management strategies in the design of subsea oil and gas production systems is critical for prevention of solids deposition such as hydrates and wax formation during turndown and shutdown scenarios. Passive insulation provides no control of fluid temperature and forces the operator to depressurise the pipeline following a shutdown and ‘no touch’ period i.e. time after which the fluid falls below the hydrate temperature. For deep water and ultra-deep water applications this approach would be ineffective as the large riser static head would prevent the pipeline pressure being reduced below the hydrate formation pressure. In these cases there is a requirement for active heating or dead oil flushing. Active heating provides the capability to monitor and control the fluid temperature during start up, shutdown and turndown operations. Several electric and hot fluid circulation active heating systems are in operation as part of bundle or pipe in pipe systems. This paper will review current active heating system designs in pipe-in-pipe (PiP) and bundle systems. In light of recent projects that have employed hot fluid circulation systems, the flow assurance challenges and subsequent design to ensure complete system functionality across the life of field will also be discussed.

The purpose of a pipe-in-pipe flowline is to provide a highly insulated system to minimise the transfer of heat between the transported fluids and the surrounding ambient environment. The dry environment between the concentric pipes allows high performance dry insulation to be used, ultimately achieving a thermal performance greater than that which is possible with a simpler wet insulated flowline. For the exploitation of High Pressure / High Temperature (HP/HT) reservoirs, a pipe in pipe system can provide the necessary thermal insulation and the integrity for transporting hydrocarbons at high temperatures above 120°C – the current limit of conventional wet thermal insulation. Compared to a wet insulated pipeline, the mechanical configuration of a pipe-in-pipe is inherently more complex and consists of several components (insulation, centralisers, water stops, field joints) which all have differing heat transfer properties. The magnitude of each component’s effect on the overall thermal performance must be understood during the design to avoid either under or over insulating the system potentially leading to operational problems and/or wasted expense. However, due to the relatively complex heat transfer processes at work, very accurate quantification of the effects is often cumbersome to calculate with little or no added meaning due to greater uncertainties in other parts of the design. However, there are cases when the design comes together in a way such that a small change in insulation thickness may tip the design into requiring a larger sleeve pipe diameter to accommodate the extra thickness. As pipes are most economically purchased in standard diameters (8, 10, 12 inch, etc.) the jump from a 14 inch to a 16 inch sleeve pipe for example not only adds significant material cost, but may have huge implications to the installability of the pipeline. Hence before making the jump to a larger pipe diameter, it makes sense to first evaluate the basis for the required thermal performance (e.g. the criticality, operational and flow assurance impacts of a marginally reduced thermal performance), and also the calculation methodology – often conservative simplifications are included early on in the design when the fabrication and installation implications are not fully evaluated or understood. This article aims to provide an overview of the current thermal design approaches for pipe-in-pipe systems, and to highlight the choices available to the engineering team and the areas with scope for optimisation. The relative magnitude of the various resistances to heat transfer will be quantified, with focus on the most relevant aspects of the heat transfer with respect to pipe-in-pipes. While this paper does not address active heating, the improvements to the passive insulation discussed would directly affect the power requirements of actively heated systems.

This paper details a new flowline thermal performance control system in which the overall heat transfer coefficient (U-value) of a pipe-in-pipe system can be varied. Large scale physical testing was carried out as part of the technology qualification to verify the system and design models developed. The solution is ideally suited for the increasing numbers of High Pressure High Temperature (HPHT) field developments being made; where the fluid temperature, pressure and flowrates will change significantly over the field life. It allows a new approach to flowline thermal design and operation to be taken for various types of field development. A qualification program has been performed with independent verification body assessment of the work and results and confirms the predicted performance. This paper describes the qualification method to DNVGL-RP-A203 and associated Technology Readiness Level (TRL) assessment of the components. The physical design of the system is presented along with examples of how benefits can be realised through its use.