Opus An Offshore Platform Upending Simulation System

A man-computer system for simulating upending motions of offshore platforms has been used to study one of the largest tower structures designed by the industry to date, and the analytical results have been verified by scale model tests. The man-computer system combines the man's insight and experience with a highly interactive computer's accuracy and speed, permitting synthetic yet adequate understanding of complicated hydrodynamic phenomena. Scale model tests have demonstrated that the man computer approach to understanding upending motion is valid, and have substantiated the concept that an interactive analytical system based on rudimentary physical principles can contribute significantly to planning a far-reaching scale model test program. 1. INTRODUCTION 1.1 Tower Upending Studies The development of petroleum reserves in the far offshore has brought new demands on the designs of the fixed platform structure that supports offshore activities. Greater water depths, more severe environmental conditions and increased operating deck loads demanded by the economics of development and production have combined to make the platform structure not only taller and wider, but far heavier than once envisoned or considered practical. The erection of the larger platform has acquired a new complexion as well. Because of its size, no longer can the structure be hoisted at its top by a' barge crane and allowed to sink to vertical. Rather, a ballasting scheme must be developedand carefully tested to effect a controlled upending motion that will jeopardize neither the tower nor the support vessels attending the erection operation. Thus, from a structural configuration with sufficient integral buoyancy to float the tower, a scale model is usually used to test in a tank a predefined erection operation, the model performance generally being accepted as representing how the prototype will respond. If the original design was good, the dual requirements of a structurally sound configuration and a hydrostatically stable and controllable body will have been simultaneously achieved. This good fortune, however, is sometimes not the case: while a design might satisfy all in place structural requirements, the upending operation might be hazardous or not possible at all. Thus, a new design cycle might be necessary. Analytical studies of upending motion by computer have become more common throughout the industry, both to assist in designing a configuration with adequate integral buoyancy, and to predict an upending trajectory and floating stability. Analytical studies provide the structural engineer and naval architect an opportunity to experiment with different structural configurations, to test in a preliminary way whether the structure can be upended, and to specify that a scale model of only a feasible structure be built. The naval architect especially benefits from analytical studies in that a broader based model testing program can be planned in advance; that is, he can determine what should and what should not be studied in the model test program. With a comprehensive program planned, he can perform only those tests that yield important information about upending not revealed by the analytical investigation.

Tubular joints are integral components of offshore structures and as such, many codes and standards address their design. The fatigue damage process of tubular joints in offshore structures is inherently variable and uncertain. In addition, potentially, there are important bias and uncertainties introduced by the analytical models used in design codes and standards. Therefore, in the development of reliability based fatigue design and requalification criteria, it is important to recognize these differences and to develop the best estimates of joint fatigue durability. This paper summarizes a study to identify the primary sources of bias and uncertainty associated with assessment of fatigue lives of tubular joints in offshore platforms. Based on the extensive screened test data, the important uncertainty sources of tubular joint fatigue durability has been examined, and the uncertainty models are developed to facilitate development of reliability based fatigue design and requalification criteria and fatigue inspection guidelines for tubular joints in offshore platforms. Introduction The development of the reliability based offshore platform design and requalification guidelines involves defining the scope (class of structure, load cases, etc.) and code format - including definition of characteristics values; selecting reliability measures; assessing uncertainties in loads and resistance; establishing target reliability levels; and determination of factors of safety, and load and resistance factors. Tubular joints are one of the main technical problems and high cost areas in the design, construction and maintenance of steel, template-type offshore structures. The uncertainty assessment of the tubular joints is therefore one of the most important components in the development of the reliability based design and requalification criteria for offshore platforms. The nature of uncertainties of the joint capacity and durability and methods for their modeling and analysis is a key in reliability based structural design of offshore platforms. Similarly, it is a key in development of realistic inspection and maintenance programs for these structures. In the context of development of criteria for design and requalification of platforms1 and floating facilities2 in the Bay of Campeche and development of inspection and maintenance programs for these facilities3,4, this study was intended to address a paradox that had developed from inspections of platforms in the Bay of Campeche.5 This paradox was that when inspections were made of joints in older platforms that were evaluated using detailed fatigue analysis methods6 to have fatigue lives that were in the range of months to years, no cracking could be detected. However, damage was found at other joints where it was not predicted or expected.5 This raised the question of: what was the confidence with the fatigue analyses? The objective of this paper is to summarize development of uncertainty models of the fatigue strength of tubular joints. Following a brief review of uncertainty of tubular joint fatigue durability, the sources of uncertainties in tubular joint fatigue durability are logically organized and quantitatively and qualitatively evaluated. Based on this evaluation, the uncertainty models are developed to facilitate development of reliability based fatigue design and requalification criteria, and guidelines for the inspection and maintenance of template-type offshore platforms.

The structural analysis and design of the Heidrun tension leg platform presented many technical Challenge a that had to be overcome in a fast and efficient manner to meet the demands of a very tight schedule. Some are inherent in the nature of a compliant structure such as a TLP with its complicated interaction between the structure, the mooring system and the environment and the importance of proper weight and at ability control during the different phase a of construction and operation. However, many other a were unique to the Heidrun platform. The Heidrun hull is the first large offshore structure built entirely of high strength lightweight aggregate (LWA) concrete. The topside modules form an integral component of the structural system of the platform. The interface between the steel topside modules and the concrete hull proved to be a very complex engineering task requiring very detailed analyses, tight fabrication and installation tolerances as well as testing of a number of key components. Ringing loads were included in the structural design of the platform for the first time in an offshore structure. The transportation of the large topside modules, mounted transversely on barges, and their mating to the hull was unique. The reserve capacity built into the design to provide additional safety in the critical components of the structure. The paper presents an overview of the multitude of challenges encountered during the detail design of the platform. Introduction The Heidrun TLP introduced several structural innovations not seen previously on any offshore platform. Examples of these include the concrete Module Support Beams (MSBS) as a main structural member of the platform and for supporting the topside modules, unique solutions for connecting the topside modules to the substructure, exclusive use of high strength LWA concrete in the construction of the hull, design and fabrication of very large diameter columns, and design of the platform for the structural effects of ringing. This paper gives an overview of the structural analysis and design activities required in connection with the development of the Heidrun TLP and concentrates on design aspects which are novel or required more extensive consideration due to the nature of the TLP configuration or construction method. A short description of the platform is provided followed by the most significant aspects of thehydrodynamic and structural analyses. Special analyses and some of the unique design considerations associated with the hull and topsides design are presented. For completeness brief descriptions are given of the construction sequence of the hull, the foundations and the independent design verification performed for the structural design.

An experimental study on transporting a free-float capable tension leg platform for a 10 MW wind turbine in waves

This paper presents a procedure a coupling of the finite element method and normal mode technique for obtaining the elastic dynamic response of offshore platforms subjected to arbitrary time and space-dependent forces. The finite element method deals with the complexities of the actual problem by reducing it to an assembly of structural elements, with known elastic and inertial properties, connected together at a discrete number of points on their boundaries. The normal mode technique is then used to reduce the resulting matrix equation of order N to the solution of N single degree-of-freedom equations with certain constraints on the assumed form of damping. An example analysis, utilizing this procedure and an actual offshore platform under the action of two different types of dynamic forces, is presented. These forcing functions are: wave forces as determined through the use of a fifth-order gravity-wave theory and seismic forces as generated by the north-south component of the May 18, 1940, El Centro, California, accelerogram. The platform is assumed to respond according to the assumptions associated with the Bernoulli-Euler beam and bar theory. INTRODUCTION In the field of offshore platform analysis and design, as in many other fields, the tools of analysis are derived through an evolutionary process. As knowledge and ability increase for more accurate prediction of the environmental forces on platforms, the methods of analysis must improve to maintain consistent accuracy. The American Petroleum Institute(l) in its Recommended Practice for Planning, Designing, and Constructing Fixed Offshore Platforms recognizes this evolutionary process and encourages designers of offshore platforms to use "all research advances available to them" The advent of high-capacity, high-speed digital computers has revolutionized the field of structural dynamic analysis. In the past the approach was to reduce the structural model to the simplest form, usually an "equivalent"single-or dual-degree-of-freedom system or "equivalent" beam or bar model for which known closed-form solutions to the dynamic equations were available. While this approach gave valuable insights into the nature of the dynamic response problem, it did not give the detailed elastic response information that is possible today. This paper presents a method which the authors believe is the next step in the evolutionary process of offshore-platform dynamic analysis. It is a combination of the finite element method and the normal mode technique. The finite element method more accurately takes into account the geometry of the system than the so-called "equivalent" methods. Although the finite element method and the normal 'mode technique have been known for a number of years, it is only with advanced computer technology that these approaches have been economically feasible for the analysis of large complex structures. This economic feasibility, the increased accuracy of predictions of dynamic forces on platforms in the operating environment, and the desire of operators to construct offshore platforms in deeper water and use them under more hostile operating conditions, will force designers to use more advanced methods of dynamic analysis.

Offshore platforms in seismically active areas should be designed to survive severe earthquake excitations with no global structural failure. In seismic design of offshore platforms, it is often necessary to perform a dynamic analysis that accounts for nonlinear pile soil structures interaction effects. This paper summarizes an inexpensive and practical procedure compatible with readily available structural analysis software (ANSYS) for estimating the nonlinear lateral response of fixed offshore platforms resting on flexible piles subjected to seismic loading. In the proposed model, piles and jacket members are modeled using BNWF (Beam on Nonlinear Winkler Foundation) and FE (Finite Element) approaches respectively in an integrated model. In this paper, nonlinear seismic response analysis of an existing sample offshore platform has been performed and sensitivity of the results to the model main parameters is investigated.

Studies for specific arctic offshore structures-drilling and production platforms, offshore terminals, piers, and underwater (under-ice) storage - confirm the advantages of concrete caissons: mass, low-temperature performance, economy, and speed of installation performance, economy, and speed of installation at the site. Stability is attained by sand and gravel fill, piles, or prestressed anchors. Text The proper development and exploitation of the resources of the Arctic Ocean requires that structures be developed which are suitable to the environment, offer a high degree of security, are economical, and are practicable for construction during the extremely short working periods available. The Arctic Ocean presents, of course, a wide spread of environmental zones, varying from the shallow water lagoons to the offshore ice pack area. Ice dominates all design criteria pack area. Ice dominates all design criteria although seismic forces on occasion may approach the same order of magnitude. The dynamic nature of ice failure by crushing necessitates that any structure have ductile behavior throughout the entire temperature range to which it may be exposed. The resonant period of the structure should be substantially longer than the period of ice crushing, that is, longer than about 1 second; thus, mass is required. Of over-riding consideration in structures planned for such widely varying and extreme planned for such widely varying and extreme conditions, is the nature of failure under overload. It cannot be brittle nor subject to self-propagating cracking. Environmental considerations require that every possible step be taken to prevent pollution in an accident. Thus, a structure for Arctic Ocean service bears a great deal of resemblance to a nuclear reactor pressure vessel. In design, one must take the structure through a whole series of limit states, each with its own probability and degree of security or safety factor. Economics play a major role also, for successful development of the resources of the arctic requires that structures and systems be economically feasible. The utilization of the resources, such as oil, is in the temperate zone Production in the arctic therefore, must be Production in the arctic therefore, must be matched with transport systems in order to be economically competitive with other sources of oil and ultimately other sources of energy.

This paper presents the design and analysis of an improved lightweight, bottom-founded, offshore platform for multi-purpose use in support of field development operations in water depths to 500 feet and possibly greater, and in severe as well as in mild marine environments. The concept, an innovation based on current tripod-type structures, utilizes a novel framing support system which results in an extremely efficient design with a broad range of applicability. The development of diverse applications for the concept and an assessment of its limits of applicability are discussed. This paper is of interest to the designer, the engineer, or others wh O are seeking an alternative, straightforward and cost effective approach to the design and installation of offshore platforms. The data presented is useful to those assessing the economic feasibility of an offshore field development. The paper discusses platform performance data, including member stresses, deflections, and natural periods of vibration, and offers criteria related to the environment, payload, and water depth for which the concept is best suited. Estimated platform weight and cost data versus water depth for various environments and development scenarios are presented and compared with data from more conventional platform concepts. It is demonstrated that the improved concept offers significant advantages over current designs. OBJECTIVE OF THE DESIGN This design concept was developed in response to the ever growing need for more cost effective solutions to the development of our offshore hydrocarbons reserves. The objective of the design was to develop an offshore structure that 1) is very lightweight, 2) has a relatively high deck load capacity, 3) is suitable for use in a large range of water depths, 4) is adaptable for the pre-drilling and completion of wells, 5) can be fabricated in a relatively short period of time, 6) can be installed with conventional lifting and/or drilling equipment, and 7) can be easily relocated for reuse at another offshore site where the water depth differs greatly from the first site. GENERAL DESCRIPTION The basic concept is a tripod structure as illustrated in Figures 1 to 3. The configuration shown in these figures is called a "Right Angle" configuration because it appears, when viewed from the side, as a 90° right angle. The right angle configuration offers greater access for the drilling of wells. In a "symmetrical" configuration the apex of the tripod is placed at the centroid of the triangular base. The symmetrical configuration is suitable for those applications that do not have wells. The principal component of the structure is the column. The column is designed as a separately installed element which is lifted or floated into place offshore in a single piece. It may contain risers, umbilicals, sumps, caissons, and other facilities as needed for offshore operations. The column is designed to support a cantilevered equipment deck.

In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures. The structural integrity of platform components under the maximum and minimum operating loads of environmental conditions is required for risk assessment and inspection plan development. In-place analyses have been executed to check that the structural member with all appurtenances robustness and capability to support the applied loads in either storm condition or operating condition. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The analysis includes interpretation of dynamic design parameters based on the available site-specific data, together with foundation design recommendations for in-place loading conditions. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have important effects on the results of the in-place analysis behavior. The result shows that the in-place analysis is quite crucial for safe design and operation of offshore platform and assessment for existing offshore structures.

Design basis accidents and accident analysis with particular reference to offshore platforms

API RP2A WSD is a design code in practice for design of jacket platforms in the Persian Gulf but is based on the Gulf of Mexico environmental condition. So for the sake of using this code for the Persian Gulf, it is better to perform a calibration based on this specific region. Analysis and design of jacket platforms based on API code are performed in a static manner and dynamic analysis is not recommended for such structures. Regarding the fact that the real behavior of the offshore jacket platforms is a dynamic behavior, so in this research, dynamic analysis for an offshore jacket platform in the Persian Gulf under extreme environmental condition is performed using random time domain method. Therefore, a new constructed offshore jacket platform in the Persian Gulf is selected and analyzed. Fifteen, 1-h storm, simulations for the water surface elevation is produced to capture the statistical properties of extreme sea condition. Time series of base shear and overturning moment are derived from both dynamic and static responses. By calculating the maximum dynamic amplification factor (DAF) from each simulation and fitting the collected data to Weibull distribution, the most probable maximum extreme (MPME) value for the DAF is achieved. Results show that a realistic value for DAF for this specific platform is 1.06, which is a notable value and is recommended to take into practice in design of fixed jacket platform in the Persian Gulf.

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleum engineering. Summary Offshore production operations play a major and expanding role in the oilindustry. Compared with land operations, offshore operations typically requiremore planning because of the more complex systems, planning because of the morecomplex systems, equipment, and logistics involved. Higher completion rates andreserve bases are necessary to justify the high cost of developing offshorefields. Future exploration and development activity is trending toward deeperwater and more hostile environments, and innovative engineering and operatingtechniques will continue to be required to meet these challenges. Introduction The oil and gas industry began producing offshore in the late 1890's near Summerland, CA; wood wharves were built in the shallow ocean waters to supportderricks and necessary producing equipment. The industry has evolved andexpanded so that the number of offshore producing platforms now approaches 10,000 worldwide. Technology also has evolved for offshore production with specialized engineering and research in oceanography, platform construction anddesign, and production systems design. Today, offshore oil represents about 25% of the world's oil production. Themap in Fig. 1 shows the offshore basins in which industry is actively exploringand producing. It is evident that these offshore basins hold the key to future international oil supplies and that the petroleum industry must continue tomeet technological challenges in both established and frontier locations. Offshore production operations present a unique set of engineering andoperating problems compared with operations conducted on land. Developing fields offshore requires larger investments because of higher drilling and producing costs, transportation and logistical problems, and the need for aplatform base on which to conduct operations. For example, in 1983 the averageoffshore well drilled in the U.S. was twice as deep and four times as costly asthe average U.S. onshore well . Fields developed offshore, therefore, must becapable of producing at greater flow rates and in sufficient volumes to makethese significantly higher investments attractive. This paper provides anoverview of offshore production operations and keys on the major differences between offshore and land production operations, which include producing production operations, which include producing structures, well completions, production handling systems, operations organizations, and logistics. Offshore Structures The most obvious condition that sets offshore operations apart from those onland is the water itself. The offshore environment can range from shallow in land lakes and protected bays to deep, unprotected seas and oceans. Most operations offshore are conducted in water depths less than 300 ft [91 m];however, operations in water depths greater than 1,000 ft [305 m] now areoccurring frequently and will become more common with the advent of deep water technology. A platform must be constructed to support operations offshore, and special consideration is given to site-specific development and environmental conditions when designing the platform decks and structure. JPT P. 583

In December of 1988 a joint venture led by Freeport Sulphur Company discovered a major brimstone deposit of 67,000,000 long tons twenty miles offshore in the Gulf of Mexico. At a production of 2 million tons of sulphur per year this facility will be in operation for the next 30 years. This paper will cover the process of automating the frasch sulphur mine including design and planning, redundancy, reliability, training and configuration. A description of system architecture which allows information for production to be gathered and handled at the facility from process control, production and drilling will be presented. The ability to monitor and control the offshore platform from an onshore facility via satellite communications and the ability to network the process control system with a local area network of host and personal computers will be discussed. INTRODUCTION Main Pass Block 299, is located (Fig. 1) in 210 feet of water, 20 miles east of the mouth of the Mississippi River in the Gulf of Mexico. The production facilities will incorporate the latest technology based upon previous applications, the company's expertise in offshore sulphur mining and on proprietary mining techniques that use seawater in sulphur mining. The offshore production facility will be installed on a series of offshore platforms (Fig. 2) linked together by more than a mile of bridges. The Main Pass facilities are scheduled for completion in late 1991 with sulphur production beginning soon thereafter. One of the greatest tools in assisting operations achieve high safety and efficiency goals is through production automation. Improved productivity as well as improved management of production information can be realized from a modern process control system. Through automation and remote monitoring, operating costs can be reduced and production revenues increased. The strategy was to implement a completely integrated information system - one that gives the association of the process operations data with management and business systems data. AUTOMATION PROCESS Planning There are a great number of factors to consider when developing a plan for plantwide process control and flow of information. The needs and requirements of production planning, engineering, maintenance, material handling, scheduling and overall management are unique when it comes to process control data and business information systems. The first step in the planning of the control system was assembling a team of people from the various areas listed above. The company had to make a decision to make available the best that the company has to offer in the areas of production, maintenance and engineering to be a part of the team. Because of their other responsibilities in construction of this facility as well as running existing facilities it is almost impossible for them to spend a majority of their time on process automation alone. Once a team was established then the next step was to set the criteria for controlling the process and the handling of production data.

Hurricanes Ivan, Katrina and Rita passed through over 3,000 platforms in the Gulf of Mexico during 2004 and 2005. While most structures performed adequately, 123 were destroyed and over 183 had major above and or below water damage. There was no life loss and no significant pollution, which is a tribute to the Minerals Management Service (MMS) oversight and American Petroleum Institute (API) design codes, specifically API RP2A (RP2A) for the structural design of fixed offshore platforms. RP2A has evolved considerably over the past 38 years since its first edition in October 1969. Some of this is attributable to changes in engineering practice and the results of experimental studies. Some is attributable to the experiences and lessons learned in large storms and hurricanes. These three recent hurricanes resulted in the largest number of destroyed and damaged platforms in the history of Gulf of Mexico operations. There are several industry, API and MMS studies underway to understand what went right and what went wrong, and to update industry guidelines and practices accordingly. This paper presents the initial results of a study performed for the MMS on the performance of fixed platforms in these hurricanes. The paper also ties-in findings of the work and its correlation to RP2A design practices. Background While hurricanes are not a welcome sight in the Gulf of Mexico, they do provide opportunity to observe how platforms perform in the storms and if required, an opportunity to update design codes accordingly. In fact, development of RP2A was in part driven by several hurricanes in the late to mid 1960's including Carla (1961), Hilda (1964), Betsy (1965) and in particular hurricane Camille (1969), which was one of the largest hurricanes to impact platforms in the Gulf of Mexico. All of these hurricanes damaged or destroyed platforms and the industry responded with the development of RP2A. In the 1970's, RP2A further evolved and the platforms were tested by hurricanes Carmen (1974) and Frederic (1979). The 9th edition of RP2A was issued in November 1977 and contained the first industry accepted wave load "recipe" including the use of 100 year return period conditions and consistent hydrodynamic drag and inertia coefficients. The 9th edition represents a substantial improvement in platform design, and is in fact demonstrated by the better performance of 9th edition and later RP2A designs in these hurricanes, as describe later. In 1985 hurricane Juan spawned in the Gulf of Mexico as a "Sudden Hurricane" and the industry was not able to evacuate all of the platforms. Several manned platforms were severely damaged, including several that toppled during the storm. Fortunately, there was no direct life loss associated with the fixed platform failures. Later investigation determined that the platforms were older vintage and in need of repair prior to Juan. It was clear that specific guidelines were required for assessment of existing offshore platforms for fitness of purpose. The industry, including significant support from the MMS, began a series of joint industry and special projects, as well as API initiatives to develop an assessment standard for existing platforms. The result was RP2A Section 17, developed in the early 1990's and originally published in 1996 as a supplement to the 20th edition. Interestingly, in 1992 during the development of Section 17, hurricane Andrew damaged or destroyed dozens of older Gulf of Mexico platforms. A hurricane the size of Andrew had not occurred since Camille and provided an opportunity to both test and then calibrate Section 17 during its development. In 2002 hurricane Lili damaged and destroyed several older platforms, something that had not been see

Using floating platforms to support offshore wind turbines will be necessary for many countries to reach their Net-Zero targets, since much of the wind resource is located at water depths at which fixed offshore wind turbines are uneconomic or technologically unfeasible. However, floating platforms for wind turbines are still at an early stage of development, and there are a wide range of platform designs. This paper reviews the current state-of-the-art of floating offshore wind turbine platform designs which currently have or have previously had a prototype, demonstration, or farm scale project at sea. The most common design goals for the platforms and the corresponding design features of platforms used to achieve those goals are reviewed. Past, current and projected future levelized cost of energy values for floating offshore wind are reviewed and discussed. The development of each platform design is described, including evolving design goals and resulting changes in platform features. Finally, overall trends in platform designs are discussed and divided into three phases, defined by changing goals: (i) influences from the offshore oil and gas industry, (ii) specialization to floating offshore wind, and (iii) further specialization to local environment.