Hutton TLP Installation

The offshore industry has spent the last several years developing semisubmersible platforms capable of supporting both drilling and production activities. The production trees are located on top of the top tensioned risers (TTRs) on a Dry Tree Semisubmersible. A key challenge in the design of these vessels is to reduce the heave motion as much as possible to enable the use of state-of-the-art riser tensioners. A model test campaign was executed as part of the developmental program. The primary objective of this campaign was to improve the accuracy of the numerical tools to be used in the design process. Riser tensioners are typically hydro-pneumatic devices, with a nonlinear tension-stroke relationship. A riser tensioner was developed at model scale which had a similar nonlinear behavior to the prototype. Examining the effect of this tensioner on the global motions was an additional objective of this test campaign. The techniques used to model this nonlinear spring is described, and its effect on global motions investigated. A key challenge in model testing platforms intended for ultra-deep water (e.g. greater than 7000 ft) is the modeling of the mooring and riser system. The premise for the design of the model mooring system is 1.) maintain as best as possible the force-offset relationship of the mooring lines and 2.) be able to describe the model test configuration in the numerical tools to be used for global design. The near taut behavior of the prototype mooring system is modeled using heavy chain and a high-catenary mooring line.

The design and analysis of a quayside mooring system for safe mooring of Prelude FLNG under extreme environmental conditions were carried out. The design of the mooring system considered the yard operation conditions and maximum wind speed during a typhoon. In order to secure the mooring safety of Prelude FLNG under an extreme environment, a special steel structure was designed between the quay and Prelude FLNG to maintain the distance from the quay to a certain extent to avoid a collision with the inclined base. The mooring safety was also ensured by installing additional new parts on the quay. A mooring analysis and mooring safety review were performed with more rigorous modeling considering the nonlinearity of the mooring rope and fender. In order to secure additional safety of the mooring system under extreme environmental conditions, a safety assessment was conducted on the failures of the mooring components proposed in the marine mooring guidelines. Based on the results of the mooring analysis, it was confirmed that the Prelude FLNG can be safely moored even under the extreme conditions of typhoons, and a worst case scenario analysis verified that the mooring system design was robust enough. The proposed mooring analysis and design method will provide a basis for the safe mooring of ultra-large floating offshore structures of similar size in the future.

The mooring system safety and the floating structure motion response in the survival condition are the main criteria in mooring system design. The safety factor of mooring system should be examined in the situation that the mooring system is intact and one mooring chain is broken. However, the previous researches mainly focus on the safety of the intact mooring system or the safety of the damaged mooring system in the steady stage. In this context, the safety of the damaged mooring system in the transient stage is investigated on a VLFS’s mooring system comprising 20 mooring lines. It is found that the effect of the breakage of the mooring chain in the transient stage is equivalent to an impact load, which will significantly reduce the safety factor of the mooring system while increasing the motion response of the VLFS. The optimal mooring system deployment in line breakage condition is further investigated by establishing a multi-objective optimization problem using NSGA-II. It can be found from the numerical results that the proposed optimal mooring system deployment technique can effectively improve the safety of mooring system while suppress motion response of the VLFS.

The purpose of this paper is to describe the authors' recent experience with the analysis, design, and installation of polyester rope mooring systems for deep water applications. Among the latest research activities, this article describes a series of full-scale tests performed on polyester rope provided for several spread moored systems offshore Brazil and West Africa. One of the main purposes of the performed tests was to determine non-linear stiffness characteristics of the rope; but other parameters used in the design and optimization of the polyester rope mooring system were also investigated. Introduction The past decade has seen a steady increase in the number of polyester rope deep-water mooring system for oil and gas exploration, especially floating production facilities. Brazil has always been in the frontier of the application of synthetic mooring ropes. Industry forecasts point to a strong increase in the number of such systems, considering the latest deepwater discoveries made offshore Brazil. Due to the past and present history of success in the use of polyester rope for the mooring of deep water floating system offshore Brazil, it is a general consensus that this trend will continue into the future and expand to other producing regions such as The Gulf of Mexico and West Africa as it can already be observed. There are many obvious advantages in using polyester ropes on deep water mooring systems. We could mention a few of them such as: lighter weight, desirable elastic characteristics and superb fatigue performance; on the other hand when engineering and installing such a system there are specific issues to be appropriately dealt with by the designer and the installation personnel. This paper will discuss some of the peculiarities associated to the design; analysis and deployment of polyester rope mooring system for deep water applications. The main topic of discussion in this article is a practical way to model the elastic stiffness of polyester mooring ropes in order to have a simple and reliable model that produces reasonably conservative extreme mooring loads and vessel-offsets. Such numeric model describing the elastic behavior of the polyester ropes have a significant impact on mooring system for floating facilities for deep water applications, with a specific application to the mooring of FPSO's. Typical Polyester Rope Mooring System for Deep Water FPSO Applications Fig. 1 depicts a typical deep water FPSO spread moor system. Each anchor leg is constituted by two segments of chain, one located at the bottom and the second close to the surface; joined by a single or multiple segments of polyester rope. In case of the mooring system shown on Fig. 1 we can see three (3) segments of polyester rope joined by two (2) short segments of chain.

In recent decades, the emphasis on renewable resources has grown considerably, leading to significant advances in the sector of wave energy. Nevertheless, the market cannot still be considered as commercialized, as there are still other obstacles in the mooring system for wave energy converters (WECs). The mooring system must be designed to not negatively impact the WEC’s efficiency and reduce the mooring loads. Firstly, the overview of the types of wave energy converters (WECs) are classified through operational principle, absorbing wave direction, location, and power take-off, respectively, and the power production analysis and design challenges of WECs are summarized. Then, the mooring materials, configurations, requirements, and the modeling approaches for WECs are introduced. Finally, the design of mooring systems, including the design considerations and standards, analysis models, software, current research focus, and challenges are discussed.

A shallow water disconnectable STL turret mooring and riser system has been developed for water depth between 30 and 50 m. This technology is based on APL’s disconnectable STL (Submerged Turret Loading) and STP (Submerged Turret Production) technologies which had been widely applied for water depth between 70 m to 2600 m for FPSOs and LNG offshore terminals. The advantage of disconnectable system is that the mooring and riser system can be designed to a preferred sea state. When the sea state is higher than design sea state (like hurricane), the vessel can be disconnected and sail away. The shallow water STL system consists of STL buoy, mooring lines, riser system and landing pad. The interface with vessel is the same as traditional STL system. The mooring and riser system are connected to the vessel through STL buoy and can be pulled into vessel by using ship winch. Unlike traditional STP and STL buoys, the shallow STL buoy has a net weight and will stay on the landing pad when disconnected from vessel. The landing pad is designed to support the impact load from STL buoy and supply enough friction for the STL buoy to stay in position during 100-year storm. The mooring system design has taken the advantage of directionality of weather when close to the shore by using different mooring line length in different directions. Further an innovative Hold-Back-Wave riser configuration has been developed for shallow water system. The riser configuration has a larger flexibility compared to traditional wave configuration and has proved to be feasible for significant wave height at least 7 m when connected to the vessel and 10+ m when disconnected from the vessel. Model test for the disconnectable shallow water turret mooring and riser system had been performed in MARINTEK, Trondheim with a LNG re-gasification vessel model at 30 m water depth. For connected system, significant wave height Hs = 6 m and 8 m has been tested. The mooring and riser system perform well, as predicted. For disconnected system (when the buoy sitting on the landing pad), significant wave height Hs = 10 m has been tested. The STL buoy is sitting on the landing pad without significant movement and the riser system performs well. SIMO program has been used to calibrate the model test results with numerical simulations. By adjusting surge, sway, yaw damping and 2nd order wave drift force, the calibrated SIMO model agrees well with model test results and can be used for similar development.

With the global oil and gas resource development accelerating its expansion into deepwater and ultra-deepwater areas, taut mooring systems have gradually become key technical equipment. However, the complex coupling mechanism between the material parameters of polyester cables and their dynamic responses has not been fully revealed, and existing design methods mostly rely on simplified models, lacking systematic verification with real environmental data and dynamic responses. Based on on-site platform data, this study proposes a multi-dimensional integrated collaborative optimization design scheme for deepwater tension leg mooring systems, aiming to provide guidance for mooring design projects in similar sea areas and enhance the safety and economy of deepwater mooring systems. To address the nonlinear optimization challenges of multi-body coupled systems, this study establishes a time-domain multi-body coupled model of the platform-riser-taut mooring system and conducts systematic research in combination with the NSGA-II multi-objective genetic algorithm. First, a multi-body coupled time-domain simulation model is constructed based on the actual geometric dimensions of the platform structure and large-scale measured environmental data, covering wave-frequency and low-frequency dynamic response characteristics. Second, statistically representative working conditions are adopted to verify the accuracy of the model's dynamic response. Third, a global sensitivity analysis is conducted to quantify the influence weights of polyester cable parameters and reveal the main control factors of the mooring cable's dynamic response. Fourth, with API-RP-2SM as the constraint, a multi-objective optimization function of the standard deviation of mooring tension and the extreme value of platform displacement is established to solve the Pareto frontier of parameter combinations. Finally, the optimization effect is verified based on typical working conditions, forming a full-process analysis method for mooring optimization. This study provides a digital solution with practical engineering value for the design of deepwater mooring systems. The research results show that: (1) The environmental loads in the target sea area exhibit significant quarterly periodic characteristics, with extreme working conditions in the first quarter accounting for 1%. (2) The length and diameter of the polyester cable have a significant impact on mooring tension. When the length of the polyester cable increases from 1850m to 2000m, a single variable of 2.5% causes the mooring tension to change by approximately 60%. The innovation of this paper lies in proposing an optimization scheme for the mooring system based on the real data from the platform. This method combines environmental data with multi-objective optimization algorithms, breaking through the limitations of traditional empirical design. At the same time, based on the actual data from the site, representative working conditions are selected to support model verification, revealing the quantitative influence laws of polyester cable material parameters on the non-linearity of mooring tension, so as to provide real guidance for similar engineering design and construction in similar sea areas.

Production techniques and designs have been developed to take full advantage of the unique dynamic characteristics of a Tension Leg Platform (TLP). The application of the information presented in this paper could be used to economically develop deep water reservoirs considered to be marginal if conventional fixed platforms were used. Data obtained in this development program indicates that the production risers can remain connected under all environmental conditions that the TLP would experience. Included are graphs, specialized hardware designs, sketches of special operating techniques and TLP performance data. INTRODUCTION For many years, the petroleum industry has developed offshore production from fixed platforms. Initially these platforms were installed in shallow water (<100'). Over the years, fixed platforms have been used in ever increasing water depth and have established a history of proven performance. In 1977, Shell Oil Company began installation of the Cognac platform offshore Louisiana in 1025 feet of water. Deep water fixed platforms are expensive. Only large and prolific reservoirs can be considered for development using a fixed platform in deep water. Development of comparatively small reservoirs or those located in water depths beyond the economic limit of a fixed platform require alternate production concepts. One alternative that has been considered is a completely submerged seafloor production station. In 1972 the Shell-Lockheed production system was installed on a well in the Gulf of Mexico at a water depth of 375 feet. A second alternative which takes advantage of readily available semi-submersible drilling platforms and much proven equipment and techniques is the floating platform production system. The first such installation is Sedco-Hamilton's Floating Production Facility (FPF) on the Argyll Field in the North Sea. The system has been operating for approximately three years. A sub sea manifold receives prediction from four satellite sub sea wells where individual production risers transmit the flow up to the platform. After processing in onboard separators, the product is transferred through a ten (10") inch central riser back to the seafloor manifold. A Single Point Mooring (SPM) system and tankers are used to deliver the crude to shore facilities. The production and transfer risers are supported from the platform by riser tensioners which accommodate a maximum rig heave of ten (10') feet. Prudent operation of such a conventionally moored facility requires that the wells be shut-in, and that the risers be purged of oil and retrieved well in advance of weather which would impede such operations. The result is downtime and a less cost-effective program. Also, when production is resumed, flow rates are often lower. The Tension Leg Platform production system offers potential for improved production efficiency because the platform does not heave, roll, or pitch in response to wave motion. The absence of heave not only simplifies the riser design and tensioning, but also permits the risers to remain connected during all weather conditions.

Time-domain numerical simulation is generally considered an accurate method to predict the mooring system performance, but it is also time and resource-consuming. This paper attempts to completely replace the time-domain numerical simulation with machine learning approaches, using a catenary anchor leg mooring (CALM) system design as an example. An adaptive sampling method is proposed to determine the dataset of various parameters in the CALM mooring system in order to train and validate the generated machine learning models. Reasonable prediction accuracy is achieved by the five assessed machine learning algorithms, namely random forest, extremely randomized trees, K-nearest neighbor, decision tree, and gradient boosting decision tree, among which random forest is found to perform the best if the sampling density is high enough.

This paper discusses key technical issues for classing deepwater mooring systems, Special applications of new mooring components such as synthetic fiber ropes, suction pile anchors and Vertically Loaded Anchors (VLA) have been presented. This paper establishes the design criteria for synthetic fiber ropes, suction pile anchors, and VLAs. The rationale as presented is based on recent projects and research and development results from joint industry studies. Testing and installation considerations for synthetic fiber ropes and field test requirements for suction pile anchors and VLAs are reviewed and discussed. Additional design and analysis requirements for the use of synthetic fiber ropes are also proposed for a taut leg mooring system. This paper represents a summary of experiences gained through the application of these innovative mooring technologies in mooring components and anchoring devices. The guidelines set by ABS as presented in this paper are intended to enhance safety standards in marine operations while meeting the new challenge to moor floating units in deep water. Introduction With the recent explosive growth in deepwater drilling and production operations worldwide. American Bureau of Shipping (ABS) is actively involved in classification of several conversions to deepwater and new-built floating platforms including semi-submersibles, ship-shaped drilling units and tanker-based FPSOs (Floating Production. Storage and Oftloading), Most of these floating units will be moored in the ever increasing water depths. In deep water, the conventional catenary mooring systems become less stiff and have a larger horizontal spread, with much higher mooring component costs and payload penalties. To cope with these challenges, new mooring systems for stationkeeping of floating units have been developed for ongoing projects. such as those offshore of Brazil installed or to be installed. by Petrobras in 1997 and 1998. These include polyester synthetic fiber ropes. VLA and suction pile anchors applied in the taut leg mooring systems. Classification of Deepwater Mooring Systems General. ABS has established the position that the scope of classification of an FPSO system shall include three major items, Le., the mooring system, the vessel, and the production facilities [Ref. 1]. Other equipment and systems such as import and/or export risers may also be classed, if requested by the owner. Since the early 1970s, ABS has provided numerous classification services for floating production systems. Table I lists some recent projects in water depths greater than 500 meters. There are special considerations to be addressed for the design and analysis of mooring systems in deepwater applications. The key element, when it comes to novel systems involving new components such as synthetic fiber ropes, suction anchors, vertically loaded anchors, etc., is to provide a comparable and compatible safety standt1rd to that of the traditional catenary mooring with chain wire and drag embedment anchors. It is well recognized that the mooring line loads tend to favorably adjust themselves when movements of drag embedded anchors occur in the traditional catenary mooring system, This is the rationale for the safety factors of the anchor holding capacity being much lower than those of the mooring line tension,

The components of the Hutton TLP tension legs are assembled using integral rotary shouldered couplings. This taper threaded coupling was purposed designed to withstand the severe fatigue and high static loads imposed by the environmental and pretension requirements. As no previous work had been undertaken on the design of high strength taper threaded couplings for this application a carefully coordinated design and manufacturing programmer had to be developed. The paper outlines the design and analysis techniques used, together with the testing performed and the results obtained. In addition, the task of ensuring that design requirements were met during manufacture and installation wi11 al so be discussed and solutions, in particular the purpose designed electronic gauging system, described. INTROUCTION Installation of the TLP at the Hutton Field was completed on the 15th July, 1984 with the mooring system's sixteen tension leg assemblies, four at each platform corner, connected to the seabed foundations. The two days of tension leg deployment was the final test for coupling computability when components from three different manufacturing sites were connected together for the first time. A total of 256 joints were "made up" to the prescribed design limits required to ensure satisfactory performance throughout the platform operating life. Proceeding this short installation period was a design process which lasted four years and encompassed extensive analysis and testing. During this time material requirements were pushed to extremes, new attitudes were required in production and new technology introduced into thread gauging practices to enable the manufacture of couplings in accordance with stringent performance requirements. In addition the assembly and make up requirements for this coupling were more demanding than that required for conventional drill collars. MOORING SYSTEM DEFINITION Each tension leg assembly (1) comprises seventeen components as shown in Figure 1. At the upper end of each leg is a tension adjusting assembly which transfers the leg load to the hull structure via the load block assembly. The load path extends down three tension 1eg elements to the crossload bearing which is located at the base of the tension leg shrouds. A further eleven tension leg elements extend below the crossload bearing terminating at the anchor connector which locks into the foundation template. A 75mm bore is provided down the centre of each tension leg to allow hydraulic operation of the anchor connector, this is filled with a corrosion inhibitor which also acts as a couplant for the in service NDE' system. Angular displacement of the tension legs due to the horizontal motion of the platform is accommodated by elastomeric flex joints in the anchor connector and cross load bearing. The seventeen components are connected by integral rotary shouldered screwed couplings as shown in Figure 2.

With the increasing demand for key technologies in deepwater oil and gas exploration, the mooring system, a critical component for the positioning of deepwater floating platforms, plays a vital role in ensuring the stable operation of offshore oil and gas platforms under harsh working conditions. In this study, we propose an optimization method for mooring systems based on Enhanced Multi-task Genetic Optimization (EMGO). Taking a semi-submersible platform mooring engineering project in the South China Sea as an example, a multi-body coupled model of the semi-submersible platform and its mooring system was established in compliance with mooring system design specifications. A custom-developed program was utilized to generate 7,751 sets of dynamic mooring system data. Subsequently, an enhanced multi-task learning (MTL) neural network was designed to predict platform offsets and mooring line axial tensions under various working conditions with high accuracy. The optimal performance of the MTL model achieved a mean squared error (MSE) of approximately 0.044 and R-Square (R²) of 0.96. Combining the enhanced MTL model with a genetic algorithm, iterative optimization was performed to converge on an optimal mooring design parameter set tailored for the semi-submersible platform. The proposed method achieved a reduction of over 20% in maximum axial tension in mooring lines and a reduction of over 10% in maximum platform offset. The EMGO algorithm demonstrated excellent capability in high-dimensional nonlinear fitting and generalization. Validation of the optimized design was performed on taut mooring systems of three additional semi-submersible platforms, confirming the feasibility and effectiveness of the optimization method under extreme environmental conditions in the South China Sea. This study introduces an innovative intelligent design method for deepwater taut mooring systems, which significantly improves the safety and reliability of ultra-deepwater platforms. It provides valuable guidance for intelligent design in offshore and marine engineering fields.

The evaluation of existing mooring system and the development of an appropriate optimization design became the key issues in the Liuhua 11–1 FPS dry-dock updating project because this optimized mooring system has to face new challenges, such as the update of site metocean conditions, the revision of wind force coefficients due to upgraded topsides, and the additional corrosion allowance for chain links due to extra 15-year service life extension compared with the original system design. A design team was formed to give the evaluation of the existing mooring system based on mooring line tensions and offset limits according to the latest industry standard for a permanent mooring system. Since the existing mooring system marginally failed the design requirements based on the evaluation, system optimization design focused on the adjustment of mooring line pretensions has been carried out to improve the mooring system performance and eventually to satisfy the classification requirements for the tension safety factors and the platform offset limits driven by the riser designs. The mooring system analysis was conducted in time domain. The Ariane program developed by BV was used in the detailed mooring system analyses. For the calibration and verification purpose, the system evaluation and the optimization design had also been independently verified with DNV's DeepC program. Introduction The LH 11–1 oil field is located about 200km southeast of Hong Kong in the South China Sea in approximately 310m depth of water. LH 11–1 FPS, which named ‘Nanhai TiaoZhan’, is a major component of LH 11–1 oil field development. The FPS was a modified drilling semi-submersible converted from a Sedco 700 series drilling rig built in 1975 and in 1995, it was converted again to a floating production unit in Singapore and then deployed at LH 11–1 oil field, permanently moored by 11 mooring legs. The Unit is classed by American Bureau of Shipping (ABS). It was originally designed for a service life of 10 years (from 1995) and has been continuously operating for more than 15 years. At the same time, a new oil field Liuhua 4–1 (OTC-24042), about 11 km away northwest LH 11–1, was in development planning with the utilization of LH 11–1 FPS facilities through a subsea tieback. Therefore, additional topsides capacities and the life extension of this aged semi-submersible FPS became necessary. CNOOC Ltd, Shenzhen is the owner of this LH 11–1 FPS. COOEC was selected as the contractor for the engineering and construction support of this FPS dry-docking upgrading and life extension project. CSSC Guanzhou Huangpu Shipbuilding Co., Ltd was contracted by the owner as the dry-docking shipyard for the upgrading construction.

An integrated positioning system was developed to control the deep water installation (2,910 ft) and to provide long term X Y Z position monitoring of a submersible platform and its mooring system. After review of requirements and tentative installation procedures, a set of system performance requirements were created to guide system design and development. Development was done with frequent project team reviews to allow inclusion of refinements in positioning system requirements and installation procedures. Software simulation hardware testing, and operational simulations were performed. System field configuration and operations to install and monitor the unmanned semi-submersible platform is presented. INTRODUCTION This paper addresses the design, development, and use of a deepwater integrated positioning accuracy to perform system Installations. In addition, this system is used to perform long term position motion monitoring in very deep water. A critical problem to very deep water floating system installations is the ability to optimize structures and theirs mooring systems for survivability, ease of installation and overall cost. As installations move into very deep water (Le. greater than 2,000 ft) a significant cost saving can be realized by optimizing mooring system design. It is the author's belief that if installation control and positioning accuracies can be provided with a high degree of confidence and accuracy, deep water mooring system designs can be made more efficient, resulting in reduced costs of hardware, installation equipment, and installation time. The Naval Civil Engineering Laboratory (NCEL) is conducting a research and development program focusing on small deepwater semi-submersibles [1]. A principal effort in this research is the Motion Measurement Experiment (MME) which is an at-sea testing program involving a large-scale small semisubmersible moored in 2910 ft. of water [2]. A development effort began in late 1985 for a positioning system, and a navigation and survey plan for the MME. The subject of this paper, the MOSNAV 300 Integrated Navigation System was developed as a result of NCEL's project requirements. The positioning system was designed to perform two major independent operations:position vessels and systems to install moorings and the platform,perform unattended long term monitoring of platform X Y Z displacements and possible anchor movements. Figure 1 presents the final platform site installation system configuration. Significant aspects of the installation sequence included,real-time positioning of two independently operated Installation vessels,monitoring of the suspended mooring segment between the two vesselshigh accuracy real-time point positioning and orientation of each mooring segment on the seafloor. All operations were managed from a single command and control room onboard the Navy installation vessel. Important functions of the unattended X,Y,Z position data collection system include the ability to monitor anchor posltl0ns relative to the seafloor transponder array and acoustic telemetry of seafloor positioning data to a collection package onboard the platform.

Mooring design of offshore aquaculture platform and its dynamic performance