bluuebunny/crossref_metadata_2025_split huggingface dataset:
Turret Mooring System Design and Analysisfor Harsh Environments
Authors: Huang Ken , Judge Sandra 
Published: October 2008

Abstract
This paper discusses key factors that must be considered in the design and analysis of internal turret mooring systems for ship-shaped FPSO vessels in harsh environments. Peculiarities of this type of mooring system, such as extreme sensitivity to non-collinear environments, excessive vertical motions at the fairlead, and complicated thruster control strategies, require that design and analysis of the mooring system be closely interrelated to other subsystems such as turret and riser systems, as well as to the vessel itself. In addition, the selection of the mooring design code that will be followed can have a significant impact on the final mooring line tensions derived and it is important to understand the types of analytical approaches that can be used as well as their limitations when applied to turret moored vessels. Model testing, especially for turret moored FPSOS, can prove particularly beneficial if properly planned. With advance knowledge and understanding of the possible implications of all these factors, trade-offs in the design can be properly evaluated.

Introduction
In recent years Floating Production, FPSO mooring system Storage and Offloading (FPSO) systems have &en gaining popularity due to the cost effectiveness of developing marginal fields with expected production lives of less than 10 years. ?Ilk is especially true when these fields are located in remote areas lacking the support of infrastructures such as existing pipeline networks. One type of application that is becoming more prevalent is the internal turret moored FPSO tanker. As these vessels move into deeper waters with harsh environments, the design of their subsystems, including moorings, turrets, and risers, becomes critical. These three key subsystems are interrelated. The riser design will determine the vessel offset criteria for the mooring system design. The mooring line loads have to be transferred to the turret for structural strength analyses. The turret location will affect not only the weathervaning capability of the vessel, but also the dynamic loads on the mooring lines due to the vertical motions at the fairlead The turret design may place restrictions on the number of mooring lines allowed, and the layout of the mooring lines may pose interference concerns for the risers, It is important to understand how these subsystems are related, and why many aspects of the design or analysis of the mooring system for a turret moored FPSO must be carefully approached.
Other important considerations for turret moored FPSOS, particularly in harsh environments, are the selection of the mooring analysis procedures and the design cede. Theenvironmental loads on the vessel, the motions of the vessel, and ultimately the mooring line tensions are all impacted by the type of analysis performed and details of the code requirements. The mooring analysis procedure generally followed today for turret moored vessels were developed for more conventional semisubmersible-type mooring systems, and the resulting limitations should be understood.
The Hydrodynamic Model Testing for Closed Loop DP Assisted Mooring
Authors: Aalbers A.B. , Merchant A.A. 
Published: October 2008

Abstract:
Far East Livingston Shipbuilding (FELS) is presently completing the construction of the Smedvig Production Unit SPU 380, which will be operated as FPSO for Esso BALDER Field Offshore Norway.
In good cooperation with FELS and ND&A Inc. of Houston an extensive model test program was carried out for approval and optimization of the DP assisted mooring system. The main aspects were:Investigate the performance of the mooring in two water depths, i.e. 250 m and 70 m.optimization of DP control for the three azimuthing thrusters.Measurement of motions and wave induced loads at e.g the bilge keels, keel and deckhouse front.Determination of limit sea state for turning the vessel around against the weather.
The tests were carried out in the Wave and Current Basin of MARIN, using a closed loop DP control system to steer the thrusters.
The paper presents the findings with respect to the effect of DP control strategy on mooring loads and present selected results of wave induced loads on bilge keels and deck house.

Introduction
In 1994, the SPU 380 construction was started on speculation. Therefore the model test investigation of its mooring covered a range of water depths. The main dimensions of the vessel are given in Table 1. II is an FPSO concept with a drag chain turret located at about 30 m forward of the midships, see Fig. 1. Nowadays, turret mooring concepts are considered the most economicalSPM systems, since the reliability of high pressure flexible risers has been proved and the technology of catenary moorings has developed to high standards of refinement with the use of composite mooring arrangements. Basically, two mooring concepts are in the market: passive moored and DP assisted moored F(P)SO'S. The passive systems stem from a past of single point moorings withfully rotatable fluid swivels e.g on the Tazerka (SALS, 1982) and Central North Sea (1996) FPSO'S, The DP assisted concepts were developments from drillship technology through e.g. the Petrojarl vessel in 1986 [o the Gryphon A FPSO in 1993.
In DP assisted mooring on a drag chain turret, as for the SPU 380, jumper hoses are used instead of a continuous multistack fluid swivel. The presence of the DP system allows to turn the vessel in moderate sea conditions to uncoil the jumper hoses. The deckhouse is placed at the bow, upwind of the process area and turret area. Due 10 the heading control that can be exerted by the thrusters, the permanent mooring on a turret located relatively far aft the bow is feasible, see e.g Ref. [1].
For the SPU 380 the mooring consisted basically of a 92 mm (3.75'), 10 leg chain system, connected to winches and running out through fairleads below the keel of the turret.
Atlantic Alliance: The Next Generation Tension Leg Platform
Authors: Logan B.L. , Naylor S. , Munkejord T. , Nygaard C. 
Published: October 2008

Abstract
Since 1990, the technical and commercial environment in the oil and gas industry in the U.K, has seen a step change in relationships. This has contributed to significantly improved development cost and time parameters. By harnessing the potential energy and expertise in the market place, many more marginal fields are now below brought into production. This paper gives an insight into the exceptional results that can be achieved by bringing together complementary skills and expertise, having a common vision for the future.

Introduction
The Atlantic Alliance (AA) is a joint venture formed by the AMEC and Iaing groups from the U.K. and the Aker group from Norway. AA came together in late 1994 for BP's prequalification process for deepwater solutions for the UK North Sea and Atlantic waters. 1 Msprocess resulted in AA being rated as 'best in class' by BP for a concrete tension leg platform, AA were then invited to participate in a design competition against other consortia with alternative solutions, for the second West of Shetlands development known as Atlantic Frontier Programme II (AFP II). The AA proposals were based on a down scafed version of the first concrete TLP by Aker for Conoco's Heidrun field in Norway. A step changein costs and schedule were achieved but not sufficiently to win the project.
BP and AA however, felt that the relatively short bidding period had not given enough time to fully release the potential of the concrete TLP solution. A joint workshop and subsequent study brought together a selection of key individuals with Gulf of Mexico, Norwegian and U.K. related experience to explore options to radically reduce time and cost parameters. By Christmas 1995 this study work had delivered the potential for a major breakthrough for the next generation TLP. At the time of writing, this is now moving into the full concept development phase ready for its first project.

Study Process and Result
Expectation For the TLP to be retained in the development matrix as a concept of opportunity, a step change in competitiveness (versus the FPSO) must be realised. Expectations were that through this work, a concept would be defined that will realise the requisite level of step change througha CAPEX reduction of 25% from AFP IIa delivery programme reduction from commitment to 24 months from the AFP II schedule of 30 months, i.e. 20%,an installation window that is not seasonably limited, i.e. similar to a FPSO
Result The study work delivered a step change opportunity. The New Generation TLP has taken us beyond our expectations with:an estimated 30% reduction in CAPEX,a sub 24 month programme from commitment anda weather window of 12 months - in line with an FPSO.
Precise Target Prediction From 3-D Seismic Data: Case Histories From the Gulf of Mexico
Authors: Duncan Peter M. , Nester Douglas C. 
Published: October 2008

Abstract
Modern 3-D seismic datasets provide information about the subsurface that goes well beyond the accurate mapping of complex structures. Utilizing attribute analysis of reflection character, it is often possible to peer inside the structure to estimate reservoir quality and fluid content. Carefulapplication of this analysis will lead to more precise prediction of what the drill bit will find and therefore allow the confidence to drill smaller hydrocarbon accumulations.
This paper will illustrate such analysis on two prospects in the Gulf of Mexico. In both cases attribute analysis of 3-D data was successfully used to predict the presence or absence of hydrocarbons in specific reservoir intervals with a high degree of precision.

Introduction
The burden of experience now firmly establishes the importance of 3-D seismic, The first and most obvious benefit of 3-D is the improved structural image of the subsurface as a result of 3-D migration, i.e. the elimination of off-linestructures. A second benefit of 3-D is the ability to visualize the subsurface in 3 dimensions. This allows for a much greater level of certainty in most interpretations, A third benefit of 3-D takes us beyond the realm of mapping reflection times, that is locating the container, to analysis of reflection character in order to see inside the container.
Understanding and interpreting reflection character have always been parts of the explorationist 's toolkit. In the past, numerical methods designed to make such analysis moreobjective were plagued by inconsistencies related to the inaccuracies of 2-D data. Our experience is that tools such as numerical inversion (impedance estimation), analysis of amplitude variation with offset (AVO) and geostatistics can be used with some real success once a good 3-D dataset is in hand.
The tangible benefit to the exploration process of these numerical tools is the ability to quantify reserve potential and estimate risk. It is obvious that as one tries to justify drilling for smaller targets, one must be able to concurrently increasethe chance of success if reasonable economic hurdles are to be met. The following two case histories demonstrate our experiences with these tools.

Case 1: Taking Marginal Prospects To Profitability
The first case history focuses on the use of advanced seismic imaging techniques to accurately estimate reserve volumes on prospects thought to have marginal economics. With theseprospects, small reserve fluctuations can take a well from being profitable to one that you wished never had been drilled.
This example is from the offshore Gulf of Mexico and involves the analysis of a potential hydrocarbon indicator (" bright-spot") that could not be drilled from an existing platform and therefore, required the setting of a satellitestructure and a tie back to existing production facilities. The potential hydrocarbon indicator is seen in the upper right corner of the seismic line in Figure 1,
The Experimental Verification of Extreme Value Response of a Moored Tanker
Authors: Mirza Saadat , Hunstad Gry 
Published: October 2008

Abstract
For the design of a mooring system, extreme values of the motion response of Floating Production Storage and Offloading vessel moored in random seas must be investigated. The tank test results of a model of such a tanker anchored in 800m of water are analysed. The extreme valueestimation for the high and low frequency response was done by methods detailed in Naess I, and the API RP2P2.
The main conclusions are that the Gaussian method underestimates the prediction. The API RP2P underestimates the heave and the roll motion of the tanker, but shows good comparison for surge, sway and yaw. The SRSS (Square rootof sum of squares) gives results which are equivalent to the API estimation. Both the Least Square method and the Modified SRSS overestimate in some cases. The underestimation of the loading in the heave direction by the API code has been taken into account in the design.
The statistical parameters are compared with similar published data to show the dominance of the 2nd order effect on motion response and the tensions in the mooring lines. Further analysis was done by dividing the time history inoverlapping intervals as proposed by Kinoshita3. The influence on the estimation of the extreme values are discussed.
The significance aspect of the work is the prediction of extreme values from either the time series simulation or the experimental data of limited length to help in load estimation of mooring lines.

Introduction
In the future, the oil and gas industry is heading towards exploration and production in deeper waters, the ability to understand and predict the dynamic behaviour of moored floating structures is therefore of great importance. The significance of the low frequency response in relation to thewave induced responses and the total responses is an important matter.
In the analysis of the motion response of a floating structure moored in random seas, it is important to investigate the extreme values of the motion. This motion response has a quadratic component, which is normally called the slow-drift motion. The quadratic response is non-Gaussian in nature, although the total response is generally treated as Gaussian (Ref. 3).
It is known that the dynamic behaviour of moored floating structures to a large extent is characterised by non-linear phenomena. This makes experimental work particularlyimportant. For complete studies of the key phenomena of the motion behaviour of the system and the resulting extreme responses, the combination of experimental work with parallel theoretical/numerical work is often an optimal solution. The estimation of extreme values by mathematical techniques have been proposed by various authors in the past. Naess4 gave an explicit expression for probability distribution of 1st and 2nd order response. But the Formula was too complicated for practical use. Kato5 presented an approximate procedure for calculation of the combined response distribution which is much easier to use.
Full Scale Field Trial of Taut Leg Mooring using Fiber Rope and Suction Anchor attached to a Semi-Submersible Drilling Unit
Authors: Ølberg Stein , Guttormsen Tom , Molland Gunvald , Andersen Jarle 
Published: October 2008

1 Abstract
This paper describes a full scale field trial of taut leg mooring performed by Saga Petroleum ASA in August/September 1996 offshore Norway, using suction anchors and two types of fiber ropes attached to a semi-submercible drilling unit. The purpose of the field trial was to qualify taut leg mooring as an effective mooring system for floating drilling units.
The subject drilling unit was conventionally moored by 8 chain/wire lines. The field trial was based on installing two additional mooring lines consisting of one polyethylene(Dyneema) and one polyester fiber rope in a taut leg mode using suction anchors. The operation was performed in 200 m water depth.
The two large suction anchors were installed and removed from a standard AHTS vessel by use of a purpose built launching frame. This operation is normally performed by large, heavy lift vessels or crane barges.
The tension and elongation of two fiber ropes were continuously monitored and stored by a data acquisition unit at site during the trial. Additional laboratory tests of the fiber ropes were carried out before and after the field trial.
Saga Petroleum's field trial has demonstrated that taut leg mooring using fiber ropes and suction anchors is a viable and effective alternative to conventionally moored and dynamically positioned drilling units, especially in congested seafloor areas and in deep water.

2 Introduction
About 5 – 6 years ago the industry in Norway started to look into exploration drilling in deep waters (800 – 1500 m water depth). This was initiated in preparation for exploring the deep prospects offshore Mid-Norway (Mere and Vering Basins). Saga Petroleum has been working with a simplified rig concept for this application, called "The EfEx Rig" (Effective Exploration). In autumn 1995, taut leg mooring using suction anchors and fiber ropes was raised as an alternative mooring system for this rig concept.
Taut leg mooring using suction anchors and fiber ropes soon developed into a project of its own. As conventional installation of suction anchors so far has been done with expensive heavy lift vessels or barges, it was imperative to develop a more cost effective installation method. In a cooperation between a small engineering company, named Structural Engineering, and Saga Petroleum, a method of deploying suction anchors from a standard anchor handling (AHTS) vessel was developed. This was accomplished by designing a special launching frame.
Saga Petroleum found that in order to qualify this deployment of suction anchors and to evaluate the behaviour of fiber ropes in a taut leg mode, a full scale field trial would be essential. The semi-submercible drilling unit, Deepsea Bergen, was scheduled to drill a well for Saga Petroleum at the Tordis Field in The North Sea, summer 1996. Even though the water depth was only 200 m, this offered a good opportunity for afield trial as Deepsea Bergen was only to be moored by 8 out of possible 10 lines.
Design and Construction of the Mars TLP Deck
Authors: Edwards C.D. , Cox B.E. , Geesling J.F. , Harris C.T. , Earles G.A. , Webre D. 
Published: October 2008

Abstract
The Mars TLP Deck supports a payload of 15,000 tons over an area of approximately 250 feet square, weighs 7,500 tons and was designed and built over a three year period between January 1993 and November 1995.
The design of the Deck incorporated many of the learnings from the previous Auger TLP Deck. An Integrated Deck concept was chosen, but the Deck was fabricated in five liftable modules to avoid the need for offshore mating with the Hull. The interconnection between the modules was designed to ensure that Deck performed as an integrated structure inplace, and was made practical by performing the module lifts at a quayside location. Design details were developed to enhance constructability whilst ensuring long term integrity of the structure. The Fabricator played a significant part in development and review of the Design details. Large scale use of high yield (60 ksi) steel was made for the first time by Shell in a major deck structure.
The Deck modules were fabricated by McDermott Inc. at their facilities in Amelia, Louisiana. Much of the fabrication was performed in buildings, including complete assembly of four of the five modules. Major innovations in construction practice included a much more team oriented approach to the client/contractor relationships, incorporation of light weight fiberglass grating, and a cost effective approach to fire proofing the structure. A "design while build" approach enabled the cycle time for the Deck to be reduced by six months. The completed modules were transported by McDermott to Aker Gulf Marine's Ingleside, Texas facilities where module lift, setting and integration were performed.

Deck Concept
The concept for the Mars Deck was developed early in the sizing cycle for the TLP, and incorporated many of the key learnings from the construction and installation of the Auger Deck. We wished to retain the many positive features from Auger, while making some major changes aimed at cost and cycle time improvements. These major changes were:Designing a integrated deck rather than a support frame with independent modules. This made the structure lighter (by eliminating duplication of structural elements) but also made more of the structure subject to the global (and time varying) loads on the TLP. All the major modules of the deck therefore participated in resisting the global motions of the TLP.Designing the integrated deck so that most of it could be constructed inside buildings. The deck was designed to be built in five sections (which we called modules), which were then assembled and interconnected to form anintegrated deck.Assembly of the complete deck via lifting and setting rather than offshore mating. Early in the project we evaluated several combinations of inshore/offshore sites, use ofexisting or new build heavy lift equipment, and setting in final or temporary locations, to establish the safest and most cost effective means of deck assembly.