Palmer A.,National University of Singapore |
Zheng J.,National University of Singapore |
Brunning P.,Subsea7 |
Journal of Pipeline Engineering | Year: 2014
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.
Knappett J.A.,University of Dundee |
Brown M.J.,University of Dundee |
Bransby M.F.,University of Dundee |
Hudacsek P.,University of Dundee |
And 8 more authors.
Geotechnique | Year: 2012
Grillage foundations are an alternative to solid surface mudmats for supporting seabed infrastructure, offering improved hydrodynamic performance and savings in foundation material. Recent research has demonstrated that grillages can be designed to have similar vertical bearing capacity to a mudmat with the same footprint. This is extended herein by: (a) determining grillage performance under horizontal loading at constant vertical load (V-H); (b) the application and development of existing plasticity-based models for predicting performance; (c) comparing the V-H behaviour with surface mudmats; and (d) discussing the implications for design. Experimental tests were conducted in sands over a range of densities and in two different modes, representing different installation procedures. In over-penetrated tests, the foundations were installed to achieve a vertical bearing capacity V0, followed by horizontal loading at a constant vertical load with V < V0: In normally penetrated tests, foundations were installed to V0 before horizontal loading at constant vertical load with V=V0: Both normalised V-H yield surfaces and a plasticity-based simulation model are presented for use in design. Laboratory-scale grillages offer improved horizontal capacity in loose and medium-dense sands and similar horizontal capacity in very dense sand, compared with surface mudmats.
Sarkar A.,Subsea7 |
Gudmestad O.T.,University of Stavanger
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2010
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.
Damblans G.,PRINCIPIA |
Berhault C.,École Centrale Nantes |
Le Cunff C.,PRINCIPIA |
Molin B.,École Centrale Marseille |
And 4 more authors.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2013
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 , 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 , no large specific experiment or study exists for hydrodynamic flows , . Therefore no guidelines exist to help prevent or predict galloping while designing cross-sections and pipe arrangements. Until recently, only the Blevins criteria  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) . 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 , , 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.
Fowkes M.,Subsea7 |
Bryson K.,Subsea7 |
Proceedings of the Annual Offshore Technology Conference | Year: 2014
As the need to exploit offshore oil and gas deposits in increasingly challenging environments increases, the economic development and safe operation of technologies has become more critical. The requirement to sample and establish the characteristics of produced well fluids has been long established in order to provide: • Fluid composition and flow data for each well • Reservoir management philosophy • Fiscal allocation Traditional methods for sampling and testing of wells employed the use of a dedicated subsea test header, pipeline, or riser connected to test separators and individual single phase flow meters located on a surface production facility. But as production has moved to deeper water, Multi-Phase Flow Meters (MPFM) have been introduced to monitor or meter individual well production, prior to a production manifold combining the production from several wells for onwards transport in a single riser or flowline. Since reservoir and well fluid characteristics alter over their life cycle, it is essential that MPFM be recalibrated to account for this to ensure their continued accuracy. Subsea 7 has developed and operated an ROV deployed Remote Hydrocarbon Sampling Skid capable of taking separate samples from up to eight individual wells in a single dive. During operation and recovery the temperature and pressure of the samples is maintained to prevent the sample coming out of phase and prevent hydrates forming in the sample or skid pipework. On recovery the sample bottles are removed from the skid and transported ashore for analysis to allow calibration of MPFMs and for fiscal allocations to be determined.. Copyright 2014, Offshore Technology Conference.
Gair G.,Subsea7 |
Ferguson H.,Subsea7 |
Proceedings of the Annual Offshore Technology Conference | Year: 2014
The latest advances in sensor and autonomous technology provide the opportunity to change the way that future inspection and condition assessment of the subsea infrastructure is carried out. The potential for smart sensors to be an integral or retrofit able part of the infrastructure and the increasing capability of autonomous vehicles is already promoting discussions. Recent work by standards groups is producing new and robust methods of harvesting sensor data; subsea hardware suppliers are looking at increased in-suite equipment monitoring and intervention methods; the océanographie community has developed remote seabed environmental monitoring systems. These are all significant indicators that show a general trend is towards smarter systems. Some of the more significant challenges that remain in the subsea inspection arena are changing methods and practices that have been evolved over many years. It is only to be expected that the introduction of new technology will change the norms and will need to be managed. Key decision making parameters can be identified by revisiting the type and format of the measurements required to make an acceptable assessment of subsea infrastructure. Early engaging with operators, service providers, sensor manufacturer and standards groups will be essential. This paper aims to set out the key benefits that can be achieved by embracing the technology and provide a look ahead to show what future services might look like. Copyright 2014, Offshore Technology Conference.
Karunakaran D.,Subsea7 |
Subramanian S.,Subsea7 |
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2015
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.
Society of Petroleum Engineers - SPE Offshore Europe Conference and Exhibition, OE 2013 | Year: 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.
Gouveia J.,Subsea7 |
Sriskandarajah T.,Subsea7 |
Karunakaran D.,Subsea7 |
Manso D.,Subsea7 |
And 6 more authors.
Proceedings of the Annual Offshore Technology Conference | Year: 2015
Steel catenary risers (SCR) have been a favored choice for recent ultra-deep waters field developments subjected to harsh environments and large floating production units (FPU) motions. The design of SCRs in such conditions is always a great challenge where the key issues are the fatigue near the hang-off and at the touch down point; clashing between lines, especially on fields with a large number of wells and high payloads on the production unit. This paper describes the solution provided by the Buoy Supporting Risers (BSR) concept which has recently been installed in the Santos basin offshore Brazil. Subsea7 detailed the original concept of BSR system, from the design to fabrication and installation. The BSR concept combines several benefits to overcome the challenges of installing SCRs on ultra-deep waters, such as: Allowing decoupling between installation of risers/flowlines and the platform, reducing payload on the production unit, very small dynamics transmitted from production unit to the risers, resulting in significant less fatigue issues. Also, the BSR concept reduces the risks associated with clashing and interference due to the smaller dynamics when compared to traditional coupled solutions. Fabrication is also addressed to highlight main challenges associated to assembling and welding clad and lined pipelines. In this paper the key aspects of the design and qualification are presented. Due to sour and C02 service requirements for the production and water injection risers, it was decided to use corrosion resistant alloy (CRA) mechanically lined pipe for the entire line, with the exception of the top and touch down sections, where metallurgical clad pipe was used. Considering its novelty, a significant amount of qualification and testing was demanded. Among the technological innovations part of the SCR package is the first successful application of a pressurized mechanically lined pipe by reel-lay method. The solution involved an extensive qualification program, including full scale tests on vessel. The methodology and rationale to allow the application of high strain levels during spooling mitigating potential risk of wrinkling within the internal liner, had to be addressed during the detailed design by extensive Finite Element Analysis and validation tests. The SCR itself, due to de-coupling of motions by the buoy, have negligible dynamic response from vessel motions, thereby behaving almost like a static system with robust fatigue performance. The only meaningful fatigue in SCRs is due to current induced VIV and is mitigated using strakes. There was negligible potential clashing with adjacent SCRs. This paper provides a summary of design and qualification work carried for SCRs lined pipes installed in the BSR system and a discussion regarding main outcomes. Copyright © (2015) by the Offshore Technology Conference All rights reserved.
Suwarno G.,Subsea7 |
Lim G.,Subsea7 |
Proceedings of the Annual Offshore Technology Conference | Year: 2014
The most economical way to install long subsea pipeline in deepwater is using S-lay method because of the lay speed due to number of workstations. But on S-lay method, the lay vessel requires a massive structure which we called "Stinger" to bring the pipe down to seabed. A Stinger is an extension structure at the stern of the vessel which used to support the pipeline on its way to seabed. This stinger is also used to control the strain level by controlling the radius of stinger by adjusting the stinger angles and also the elevation of the roller boxes. The length and the radius of the stinger will govern the pipe departure angles which in the end, it will govern the length of pipe span on catenary as well as the tension require for pipe laying. Typically modern stinger consists of two or more space frame stinger structures and hold by stinger holding frame and stinger hitch. On each of the space frame, the pipeline will be supported by a few roller supports. This support is called "Roller Box". The Stinger radius can be adjusted by setting the "Roller Box" at desired heights and also set the angles between stinger sections. Typically during pipelay analyses, stinger is assumed to be fixed and rigid. At certain extent, this stinger structure rigidity assumption is valid. This is due to the many pipelay operations have been analyzed base on this assumption, but there must be a limitation for this assumption, which depends on the stiffness of the stinger (the flexibility of the stinger). The oil and gas pipeline project has gone deeper and deeper, and the deepwater pipeline will require a longer S-lay stinger for installation, and typically the unsupported part of the stinger also become longer, which makes the stinger behave more flexible and leads to a questionable common practice by assuming the stinger structure is always rigid in pipelay analyses. This study is about to use pipelay analyses software and structural analyses program to calculate the displacement of the stinger base on pipeline reaction load on the roller box taken from pipelay analyses. And the interaction between two softwares will be used to predict appropriate stiffness of the stinger. At the end of the study, comparison using "Rigid Assumptions" and "Non Rigid Assumption" on pipelay analyses is drawn to understand the stinger stiffness effect on the stain level, tension required and the gap on the last roller. Copyright 2014, Offshore Technology Conference.