Air Products, BHGE, Norsafe, and Sofec won contracts for Eni’s Coral South FLNG project in Mozambique. A routine maintenance project became more complicated when an ROV inspection exposed unexpected trenching that reduced the holding capacity of the system. As many platforms begin to produce beyond their design life, maintenance of mooring systems becomes more critical. With redundancies in place, operators may be unaware of initial failures, which can have major consequences if another failure occurs.
With the purchase, the growing, privately-held Chrysaor Holdings will expand its UK North Sea production to 185,000 BOE/D. The state-run offshore company has found a gas and condensate field that holds an estimated 250 million BOE. The latest example of the offshore sector's march toward automated wellbore construction will take shape later this year in the North Sea. Just 2 months after issuing more than a hundred licenses, the Oil and Gas Authority begins the process again for a whole new set of blocks. The company announced it would “initiate the process” of marketing its UK Central North Sea fields as part of a portfolio review.
Wendt, Fabian F. (National Wind Technology Center, National Renewable Energy Laboratory) | Robertson, Amy N. (National Wind Technology Center, National Renewable Energy Laboratory) | Jonkman, Jason M. (National Wind Technology Center, National Renewable Energy Laboratory)
During the Offshore Code Comparison Collaboration, Continued, with Correlation (OC5) project, which focused on the validation of numerical methods through comparison against tank test data, the authors created a numerical FAST model of the 1:50-scale DeepCwind semisubmersible system that was tested at the Maritime Research Institute Netherlands ocean basin in 2013. The OC5 project revealed a general underprediction of loads and motions by the participating numerical models. This paper discusses several model calibration studies that were conducted to identify potential model parameter adjustments that help to improve the agreement between the numerical simulations and the experimental test data. These calibration studies cover wind-field-specific parameters (coherence, turbulence), and hydrodynamic and aerodynamic modeling approaches, as well as rotor model (blade-pitch and blade-mass imbalances) and tower model (structural tower damping coefficient) adjustments. These calibration studies were conducted based on relatively simple calibration load cases (wave only/wind only). The agreement between the final FAST model and experimental measurements is then assessed based on more complex combined wind and wave validation cases. The analysis presented in this paper does not claim to be an exhaustive parameter identification study but is aimed at describing the qualitative impact of different model parameters on the system response. This work should help to provide guidance for future systematic parameter identification and uncertainty quantification efforts.
Zhang, X. Y. (American Bureau of Shipping) | Yong, F. (National University of Singapore) | Li, Y. P. (Hohai University) | Yi, J. T. (Chongqing University) | Lee, F. H. (National University of Singapore) | Chen, X. (Beijing Jiaotong University) | Wang, S. Q. (American Bureau of Shipping)
The quest for reliable and cost-effective solution of installing piles in deepwater led to the development of dynamically installed piles that embed themselves into the seabed through free-fall. Several variations of dynamically installed piles have been devised and successfully entered into service at deepwater offshore sites. The most notable one is the torpedo pile patented by Petrobras.
To facilitate the design and installation of the dynamically installed piles, ABS has developed Guidance Notes to provide geotechnical design and structural assessment methods. This paper presents an overview of the guidance and details of the technical development that forms the basis of the recommended methods.
In support of the development of the guidance, finite element analyses and centrifuge tests were conducted to study pile/soil interaction and to verify and further improve the prediction methods for pile pullout capacity. The pile inclination after installation, which has a significant effect on the pile pullout capacity and is of significant concern to the offshore industry, was thoroughly studied. Since the dynamic installation process results in lower short-term pullout capacity of the pile, it is recommended that the piles be installed for a sufficiently long period to allow the development of the pullout capacity. A prediction of the pile capacity restoration over time was developed based on the results of a series of centrifuge tests. A framework on the normalized vertical and horizontal component is proposed to predict the pile pullout capacities subjected to different loading angles.
ABSTRACT Nearshore solutions for storage and regasification of liquefied natural gas using large floating structures such as FLNGs (Floating Liquefied Natural Gas) and FSRUs (Floating Storage and Regasification Units) are becoming popular due to their economic and safety advantages. Permanent mooring systems are designed specifically to keep these large floating structures within an acceptable excursion range for the site-specific environmental conditions and design life of the structure. The typical jetty mooring arrangement commonly used for temporary berthing is upgraded to nearshore position mooring of FLNG/FSRUs. The higher mooring loads and longer design life require consideration of several factors, which are discussed here. A case study has been carried out based on the ABS Guidance Note on Nearshore Position Mooring to provide a detailed analysis procedure. The effect of bathymetry, water depth, tide, directional wind, wave and current, interaction between the mooring lines, fenders and the vessel, interaction between the LNGC (Liquefied Natural Gas Carrier) and FLNG are studied. Sensitivity of mooring load prediction to various modeling parameters is also presented. Finally, an overview of the latest industry effort of developing guidelines for the assessment of environmental loads and nearshore mooring system is given. Floating terminals are large infrastructures that provide a convenient means for the storage and regasification of liquefied natural gas.
Recent mooring research indicates that fiber ropes with higher strength and higher stiffness would benefit floating offshore platforms in water depths beyond 2000 meters in terms of reduced offset and reduced weight in comparison with polyester rope mooring. More advanced fibers with high strength and high stiffness are also entering into market. The industry has used high strength and high stiffness ropes for temporary moorings and mobile offshore drilling unit moorings. However, high strength and high stiffness fiber ropes have not yet been used for permanent moorings. This paper summarizes studies conducted by the industry on the high strength and high stiffness fiber ropes. An overview is provided for the existing research results, testing conducted, application guidelines, rope qualification processes, project experience, lessons learnt and the challenges of using high strength and high stiffness ropes for permanent moorings. Based on the industry experience of using polyester rope for permanent mooring and knowledge gained on high strength and high stiffness rope, this paper provides recommended assessments that could facilitate the application of high strength and high stiffness ropes for permanent deepwater moorings.
Deepwater drilling and production has been in existence for decades, and with it, stationkeeping philosophies and technologies have evolved with time and experience. In years past, moorings were designed purely with robustness and simplicity in mind, dropping anchors as rigs arrived on location, with the expectation to weather the storms, but now, with increased strengths seen in tropical rotating storms (TRS), ice floes, and deeper operating water depths, more sophisticated mooring components have been developed. Chain has yielded ground to wire and synthetic ropes. Stockless anchors have been replaced with piles, gravity installed anchors, and sophisticated high holding capacity (HHC) drag anchors. The connecting hardware has become “smart,” evolving from kenters and c-links to sensor and sonar-equipped remotely releasable systems.
The main drivers for this evolution have been environmental – extreme metocean events, corrosion, wear and fatigue – from the floater to the seabed and below.
This paper will present how “dumb steel” mooring systems have evolved into sophisticated and detailed engineered foundations that span miles of ocean real-estate, while allowing for a new level of vessel mobility that reduces risks to people and assets.
ABSTRACT Mooring systems of many long-term/permanent floating offshore installations (FOIs) are approaching the end of their original design life. Some FOI mooring systems are seeking life extension to support continued production/storage or planned tieback. Worldwide, many offshore mooring systems have been approved for continued service. This paper presents a state-of-the-art review of the current industry practice on mooring system life extension with an emphasis on fit-for-service technical assessment but excluding the project economic considerations for decision-making. The objective is to initiate an industry-wide approach to improve technical assessment for mooring life extension by identifying gaps and challenges. A comprehensive survey was carried out on the available policies from the regulatory authority and technical guidance from the industry. The major technical challenges are discussed covering baseline information collection, in-service mooring inspection, damage/degradation assessment of components, mooring design re-analysis, and remaining life prediction. Recommendations on technological development, industry guidance, and life cycle integrity management were made to advance the current industry practice of mooring system life extension. Recently, there is growing attention to life extension, also known as continued service, of long-term/permanent floating offshore installations (FOIs) as many of them are approaching the end of their original field life, and some of them are seeking continued production from the same or adjacent oil and gas fields. These FOIs include FPSOs, FSOs, SPARs and semi-submersible platforms, as well as offloading buoys.
Station-keeping capability of offshore oil rig is important so that mooring integrity become a critical design factor. Several unexpected accidents of chain mooring failure were related to new mechanism called Out-of-Plane Bending (OPB) and In-Plane Bending (IPB). The main factors causing OPB-induced fatigue are tension, friction, and interlink angle. To consider this mechanism during the design stage, chain interlink angles from global-system simulation should be computed accurately in time domain. The results are sensitive to the degree of accurate modeling of fairlead connection.
In this study, time-varying chain interlink angles with underwater chain stopper system (chain-hawse) are investigated with hull-mooring-riser coupled time-domain simulation program CHARM3D, which has been developed in TAMU for the past two decades. Several scenarios of chain-hawse system and environment are investigated to observe the corresponding effects on interlink angles.
Luz, Felipe F. (Federal University of Rio Grande do Sul) | de Menezes, Eduardo W. (Federal University of Rio Grande do Sul) | Cimini, Carlos A. (Federal University of Minas Gerais) | Amico, Sandro C. (Federal University of Rio Grande do Sul)
Carbon fiber reinforced polymer (CFRP) cables present outstanding performance in terms of specific stiffness and strength, but their behavior is not yet fully understood, especially regarding the influence of the cable’s construction on its properties. In this study, the mechanical performances of a standard (6+1) X 7 stranded CFRP cable composed of 49 rods (wires) and a 1 X 61 spiral CFRP cable (61 rods) under tensile and bending loading were analyzed using a numerical model. The spiral cable showed higher load at break (980 kN) compared to the stranded cable (878 kN) and higher minimum bending radius.