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.
The BP operated Greater Plutonio field development offshore Angola comprises a spread-moored FPSO in 1,300 m water depth, serving as a hub processing the fluids produced from or injected into the subsea wells. The selected riser system is a riser tower tensioned by a steel buoyancy tank at its top end and distributed foam buoyancy along a central structural tubular. The riser bundle is asymmetric in cross-section and this paper presents the work performed to determine the specific hydrodynamic characteristics of the design. Both basin tests and CFD analysis results are presented with discussion on some specific hydrodynamic issues: vortex-induced vibration (VIV) of the global riser tower system, VIV of individual risers, and the dynamic stability of the global system (i.e. galloping). Finally, guidelines for the assessment of the hydrodynamic behaviour of such system geometries are proposed. The results of this paper demonstrate that the Greater Plutonio riser bundle represents an effective solution in term of hydrodynamic behaviour and is not sensitive to VIV fatigue or galloping.
Turret-Moored FPSOs are frequently used for deepwater developments worldwide, with consideration of disconnectable turrets for harsh environment applications. This trend makes the interaction between the FPSO hull, mooring system, and riser systems a vital design parameter for arctic conditions. This paper provides a review of the various riser systems that can be considered for turret-moored FPSOs. These include proven coupled and decoupled systems (flexibles, Steel Catenary Risers, Steel Lazy Wave Risers, and hybrid decoupled riser systems), and also new riser concepts (e.g. the TCR - Tethered Catenary Riser, or the TSLWR - Tethered Steel Lazy Wave Riser). These systems are described in terms of design and functionality. These riser systems are discussed with consideration of the particular challenges of disconnectable turret-moored FPSOs and specificities of arctic conditions.
Turret-Moored FPSOs are more and more used for deepwater developments worldwide, with consideration of disconnectable turrets for harsh environment applications. This trend makes the interactions between FPSO and riser system, and the optimized selection of the riser system, of greater importance.The paper provides a review of the various riser systems that can be considered for turret-moored FPSOs: proven systems, both coupled (flexibles and rigid risers) and uncoupled systems (hybrid single and multiple riser systems), and new riser concepts. These systems are described in terms of design and functionalities; fabrication and installation methods are presented.Pros and Cons for these riser systems are discussed, with consideration of the particular challenges brought by turret-moored FPSOs (e.g. large floater motions, riser hang-off geometry constraints at turret, hang-off loads, riser interferences, riser pre-installation, turret disconnection constraints). Elements for selection of the most appropriate riser system are proposed, considering a range of project specificities.
The CLOV development is located offshore Angola in a water depth of 1,300m and includes two Hybrid Riser Towers. The first oil was successfully achieved on June, 12 2014 as initially scheduled at project award in July 2010. This paper provides an overview of the engineering scope through all phases of the Hybrid Riser Towers delivery and how such input was used to determine some key aspects of the execution plan.The paper starts with a description of the design of the Hybrid Riser Towers developed for the CLOV project. Moving through the various phases of the package (from design engineering to procurement, fabrication and offshore installation), the paper details the associated fabrication and installation methods and focuses on the engineering analyses developed to drive the design and the associated installation methodologies. A number of examples are also highlighted in which the input from the engineering analyses was used to introduce key changes to the fabrication and installation philosophies developed for past similar projects (Girassol and Greater Plutonio).The example of the Hybrid Riser Towers development on the CLOV project provides a perfect field to investigate the extent of the engineering scope of similar riser packages and how to optimize the benefit from such analyses. The Riser Tower design selected for CLOV project benefits from past experience gained on Girassol and Greater Plutonio Riser Towers (Ref.[1], [2], [5] and [7]) and consequent improvements. Significant updates to the Hybrid Riser Towers design and installation methodologies driven by the analyses from CLOV project are presented with details on the way they helped reduce technical risks and secure the delivery schedule. Based on this experience, recommendations are provided on how to best approach the engineering scope covering all phases of large and technically complex projects with tight schedule constraints.This paper provides the latest updates on state of the art engineering analyses covering design, fabrication and installation of Hybrid Riser Towers and associated installation methodologies for deepwater developments.
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