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Goodlad M.,Subsea7
Society of Petroleum Engineers - SPE Offshore Europe Conference and Exhibition, OE 2013

Subsea7 have designed, fabricated, and installed Bundles (towed pipeline production systems) for over 33 years, with 69 installed to date. Over the previous 3 decades operators choice of Bundles as a field development option has been steady but intermittent. However over recent years Bundles have been embraced by field developers as a technically and commercially attractive solution to allow difficult fields to be developed, they are now being proposed by operators and design houses at concept selection phase. Subsea7 is currently experiencing the busiest period of Bundle design/installation activity ever; a record 8 bundles installed during 2011/2012 and further 8 confirmed installations by the Q2 of 2015. A number of the installed or currently in-design Bundles are firsts for Subsea7. The paper will discuss the benefits of Bundle technology for rejuvenating and extending existing facilities or new developments. A number of case studies to demonstrate the technical and commercial advantages will be discussed; • Apache Bacchus - Active Heating of Production Fluid using produced water, • BP Andrew - Longest tie-back utilising Bundles, 4 bundles connected in series totalling 27.8km, • COP Jasmine - Highest Temperature Bundle 155°C (to PD8010), • Total West Franklin - Highest Design Temperature 160°C (to DNV) & Largest Diameter Carrier Pipe, • BG Knarr - Deepest Water Depth 410m, and integrated flow assurance design, • Shell FRAM - First Bundle with two midline structures. The technical benefits driving the increased interest in Bundle Technology for field development will be discussed; • Highly efficient insulation systems, heated bundles utilising Hot-Water or Electrical Trace-Heating, • Design/construction method allows full system integration testing onshore allowing fast hook up and commissioning offshore, low stress installation method by CDTM (Controlled Depth Tow Method) minimizes stress and fatigue on internal flowlines, • Design of bundle cross-section/system allows expansion at both ends, reducing build-up of axial forces, reducing the need for intermediate expansion spools, and allowing efficient design for HP/HT field developments, • Eliminate requirement for specialised installation vessels (Reel-lay, S-Lay, J-Lay, and Heavy Lift) by utilising readily available vessels, and incorporating subsea structures within the towed Bundle System. Copyright 2013, Society of Petroleum Engineers. Source

Sarkar A.,Subsea7 | Gudmestad O.T.,University of Stavanger
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE

The lifting analysis of a subsea structure determines the maximum allowable design sea state in which the structure can be installed safely. Normally, such analysis on the structure at the splash zone governs the expected largest forces in the hoisting system and in turn the allowable sea state since the water particle kinematics is larger in the splash zone. In this paper, the DNV Recommended Practice for Modelling and Analysis of Marine Operation (DNV-RP-H103, April 2009) is discussed with emphasis on the hydrodynamic coefficients and analysis methodology for the splash zone lifting analysis. An approach is suggested here to take into account the free surface proximity effect on added mass of flat surfaces in the absence of test results. Discussions on the following points are also included, • For structures which show restricted sea state due to large double pendulum motion and consequently high dynamic tension in the crane wire, a solution could be obtained by lowering the sling angles. • For inertia dominated structures, the drag coefficients should be chosen with caution unless experimental results are available since the drag may induce unrealistic damping in the system. • For the structural design of large subsea structures, the design DAF for submerged condition should be chosen from a preliminary lifting analysis result. The current industrial practice of using DAF = 2 with respect to the static submerged weight could be increased following the analysis result to optimise the use of the crane capacity by achieving a higher design sea state. • For lifting analysis of structures with large added mass / submerged weight, modelling of winch speed may represent a worse loading case as compared to the case with zero winch speed in the splash zone. • For the splash zone analysis, correct modelling of the stiffness of the crane structure along with the wire is important. The assumption that the crane structure is rigid may lead to unrealistic analysis results. Experimental programmes to obtain further information on the amplitude dependent characters of the hydrodynamic coefficients, the stiffness and the damping of the Crane, the wires etc are furthermore recommended. Copyright © 2010 by ASME. Source

Damblans G.,Principia | Berhault C.,Ecole Centrale Nantes | Le Cunff C.,Principia | Molin B.,Ecole Centrale Marseille | And 4 more authors.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE

Bundle arrangements are currently used in the design of underwater riser towers or oil export lines. A bundle is made of several parallel pipes linked together at intervals. Even if individual pipes are of circular section, the global external cross-section seen by the fluid is non-circular. When placed in a current, a bundle may be therefore prone to plunge instability [6], also know as "galloping". When designing such bundle's section, it is important to be able to predict its susceptibility to galloping and what are the implications on the whole structure. Galloping is taking place in a low frequency range compared to VIV but with larger amplitude, up to several diameters. Instability can also occur in torsion through a coupling effect with transverse oscillations. Riser Vortex Induced Vibrations have been studied for decades, and numerous experiments have been performed both in-situ and in model test facilities to understand and predict the instability of a slender cylindrical structure in current. The main motivation is the consequences of VIV on riser fatigue life. If galloping and related instabilities are well known in aerodynamics [9], no large specific experiment or study exists for hydrodynamic flows [1], [7]. Therefore no guidelines exist to help prevent or predict galloping while designing cross-sections and pipe arrangements. Until recently, only the Blevins criteria [1] were available to predict the risk of instability. Based on recent examples of riser tower, experimental and numerical investigations are carried out within the "Gallopan" project in the frame of CITEPH (Concertation pour l'Innovation Technologique dans l'Exploration Production des Hydrocarbures) [11]. The main objective is to propose guidelines to avoid or reduce the risk of galloping in bundle cross section design. Two cross section shapes are investigated, a square cross section for which results are available in the literature [1], [10], and a bundle cross section specifically designed to be unstable. Model tests are performed in two steps: • Captive tests and transverse forced oscillation tests in steady current to derive hydrodynamic coefficients; • Free oscillations tests in steady current to identify the range of reduced velocity where instability occurs as well as the response amplitudes. A specific experimental arrangement, based on a vertical pendulum system is used. Numerical investigations are focused on the use of a standard riser analysis tool. Hydrodynamic coefficients issued from experiments are introduced. Model test set-up is reproduced for comparison purpose. Copyright © 2013 by ASME. Source

Karunakaran D.,Subsea7 | Subramanian S.,Subsea7 | Baarholm R.,Statoil
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE

Recently turret-Moored FPSOs have been used in many deep water developments worldwide, with consideration of disconnectable turrets for harsh environment applications. This trend makes the interactions between FPSO and risers system more important. Further, Steel Lazy Wave Risers (SLWR), which is a compliant variant of the mostly commonly used Steel Catenary Risers (SCR), is becoming an attractive riser option. The paper provides a review of the various riser systems that can be considered for turret-moored FPSOs, and specific emphasis on Steel Lazy Wave Risers. A detailed case study of Steel Lazy Wave Risers for a typical turret moored FPSO with disconnectable turret is presented. This system is described in terms of design and functionalities, the fabrication and installation methods are presented. The case study shows clearly that SLWR are an attractive alternative to be used for FPSO with disconnectable turret and is very efficient to fabricate and install in a very cost effective manner. Pros and Cons for SLWR are discussed, with consideration of the particular challenges of turretmoored FPSOs with large floater motions, hang-off geometry constraints at turret, hang-off loads, riser interferences, risers pre-installation, and turret disconnection constraints. © 2015 by ASME. Source

Palmer A.,National University of Singapore | Zheng J.,National University of Singapore | Brunning P.,Subsea7 | Lim G.,Subsea7
Journal of Pipeline Engineering

FISHING TRAWLS CAN damage pipelines on the seabed. It is important to be able to predict the force on a pipeline when trawlgear is pulled over it. Analysis and comparison with full-scale measurements indicate that the conventional calculation is incomplete, but that it is usually conservative.The pull-over load has more than one component, and the components depend on the trawl velocity in different ways. The factors that need to be included in more complete models are discussed. Source

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