After suffering major setbacks, Chevron’s massive Big Foot project finally achieved first oil last November in the US Gulf of Mexico. With the setbacks in the rear-view mirror, project personnel spoke about the challenges. 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 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.
For successful floating mobile offshore drilling unit (MODU) operations, proper marine riser and mooring equipment and their management are critical. When dealing with MODU operations, there are two types of stationkeeping systems, spread mooring and DP. The vast majority of floating MODUs are equipped with spread-mooring systems. Some have a limited amount of dynamic thruster assist to their spread-mooring system. Almost all of today's semi and drillship MODUs have an eight-point mooring system consisting of anchor chain, wire rope, or a combination.
In the early days, ships were very attractive and the most common floating mobile offshore drilling units (MODUs). Ships mobilized quickly and could carry a large amount of operator consumables, such as casing and bulk mud. However, their motions in weather proved to be a significant disadvantage in even mild environments. If a ship-shaped unit was hit on its beam with even moderate swells, the roll could raise havoc with efficient productivity. The Offshore Co. (now Transocean) developed and patented the turret mooring system (Figure 1).
The growth and evolution of offshore drilling units have gone from an experiment in the 1940s and 1950s with high hopes but unknown outcome to the extremely sophisticated, high-end technology and highly capable units of the 1990s and 2000s. In less than 50 years, the industry progressed from drilling in a few feet of water depth with untested equipment and procedures to the capability of drilling in more than 10,000 ft of water depth with well-conceived and highly complex units. These advances are a testament to the industry and its technical capabilities driven by the vision and courage of its engineers, crews, and management. From an all-American start to its present worldwide, multinational involvement, anyone involved can be proud to be called a "driller." Since the beginning in the mid-1800s until today, the drilling business commercially has been very cyclic. It has been and still is truly a roller-coaster ride, with rigs being built at premium prices in good economic times and ...
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.