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[Truncated abstract] The Arabian Gulf oil and gas production reserves have made it one of the world's strategic producers since early 1960s, with many of the existing platforms stretched beyond their original design life. Advances in drilling technology and reservoir assessments have extended the requirement for the service life of those existing platforms even further. Extension of the life span of an existing platform requires satisfactory reassessment of its various structural components, including piled foundations. The American Petroleum Institute Recommended Practice 2A (API RP2A) is commonly used in the Arabian Gulf for reassessment of existing platforms. The API guidelines have been developed for conditions in the Gulf of Mexico, the waters off Alaska and the Pacific and Atlantic seaboards of the USA. However, the Arabian Gulf conditions are fundamentally different to those encountered in US waters. Hence, there is a need to develop guidelines for reassessment of existing offshore structures to account for the specific conditions of the Arabian Gulf. This thesis performs statistical analyses on databases collected during this research from existing platforms to calibrate relevant load and resistance factors for the required guidelines. The developed guidelines are based on established approaches used in developing international codes and standards such as API RP2A-LRFD. The outcome of this research revolves around the following three main issues: 1. Calibration of resistance factors for axial capacity of piles driven in the carbonate soils API RP2A (1993, 2000) does not quantify limiting soil parameters for piles driven in carbonate soils and provides a single factor to predict the capacity of piled foundations. This research identifies a set of limiting engineering parameters and calibrates corresponding capacity reduction factors to predict axial capacity of driven piles in the carbonate soils of the Arabian Gulf. ... This contrasts with Section 'R' of API RP2A (1993, 2000), which focuses on extreme environmental conditions when performing reassessment. The probabilities of failure considered in this research do not include errors and omissions (controlled by quality assurance procedures) or material deterioration (controlled by choice of materials, detailing, protective devices, and inspection and repair procedures) or reliability-based maintenance. Addressing operating overload conditions requires attending to two issues, namely the capacity of piles driven in carbonate soils and OALL, which have been addressed in this research. The operational overload situation is likely to occur during shutdown condition or during drilling or work over activities where significant OALL are usually applied to platform decks. Such operational overload can be managed by placing signs at various open areas on the platform nominating the maximum load limits (kPa), introducing procedures that ensure that maximum load limits are not exceeded during operation and management of human behavior by reinforcing the importance of following the procedures. The outcomes of this research are expected to have a profound influence on reassessment of existing platforms in the Arabian Gulf.
The Arabian Gulf oil and gas production reserves have made it one of the world's strategic producers since the early 1960s, with many of the existing platforms stretched beyond their original design life. Advances in drilling technology and reservoir assessments have extended the requirement for the service life of those existing platforms even further. Extension of the life span of an existing platform requires satisfactory reassessment of its various structural components, including piled foundations. The American Petroleum Institute Recommended Practice 2A (API RP2A) is commonly used in the Arabian Gulf for reassessment of existing platforms. The API guidelines have been developed for conditions in the Gulf of Mexico, the waters off Alaska and the Pacific and Atlantic seaboards of the USA. However, the Arabian Gulf conditions are fundamentally different to those encountered in US waters. Hence, there is a need to develop guidelines for reassessment of existing offshore structures to account for the specific conditions of the Arabian Gulf. This thesis performs statistical analyses on databases collected during this research from existing platforms to calibrate relevant load and resistance factors for the required guidelines. The developed guidelines are based on established approaches used in developing international codes and standards such as API RP2A-LRFD. The outcome of this research revolves around the following three main issues: 1. Calibration of resistance factors for axial capacity of piles driven in the carbonate soils 2. Development of open area live loads (OALL) on offshore platforms 3. Effect of extreme storm conditions on the reliability of existing platforms in the Arabian Gulf The outcomes of this research are expected to have a profound influence onreassessment of existing platforms in the Arabian Gulf.
This book presents a study for the determination of environmental load factors for Jacket Platforms in Malaysia and a methodology to determine the life extension of aging platforms. The simplified methods described here could be used for determining not only structural reliability but also safety factors. Its content is particularly interesting to design and maintenance engineers who are working in offshore or onshore industry.
Offshore Risk Assessment was the first book to deal with quantified risk assessment (QRA) as applied specifically to offshore installations and operations. Risk assessment techniques have been used for more than three decades in the offshore oil and gas industry, and their use is set to expand increasingly as the industry moves into new areas and faces new challenges in older regions. This updated and expanded third edition has been informed by a major R&D program on offshore risk assessment in Norway and summarizes research from 2006 to the present day. Rooted with a thorough discussion of risk metrics and risk analysis methodology, subsequent chapters are devoted to analytical approaches to escalation, escape, evacuation and rescue analysis of safety and emergency systems. Separate chapters analyze the main hazards of offshore structures: fire, explosion, collision, and falling objects as well as structural and marine hazards. Risk mitigation and control are discussed, as well as an illustration of how the results from quantitative risk assessment studies should be presented. The third second edition has a stronger focus on the use of risk assessment techniques in the operation of offshore installations. Also decommissioning of installations is covered. Not only does Offshore Risk Assessment describe the state of the art of QRA, it also identifies weaknesses and areas that need further development. This new edition also illustrates applications or quantitative risk analysis methodology to offshore petroleum applications. A comprehensive reference for academics and students of marine/offshore risk assessment and management, the book should also be owned by professionals in the industry, contractors, suppliers, consultants and regulatory authorities.
This study proposes new methods for the reliability-based design of structural systems, with emphasis on offshore mooring systems. After a brief introduction to the mooring systems, two main objectives are discussed in this dissertation. The first objective is the calculation of the probability of failure of a structural system, which is an important input for a reliability-based design or any quantitative risk assessment. Two different methods are proposed for calculation of the probability of failure: a method based on the Monte Carlo simulations and a method based on the basic rules of probability, which is called the Progressive Reliability Method (PRM). Both methods are flexible to the definition of system failure. For example, the probability of a serviceability or ultimate-strength failure can be assessed using any of the two methods. It is shown that the two methods produce similar results, but PRM is preferred because it is exact and usually faster to implement. The second main objective in this dissertation is to develop a method for the optimization of the design of a structural system, given a target probability of failure. In this method, using the structural analysis of a preliminary design, the ratio of the optimal to the preliminary mean capacity of each component, which is called the Optimality Factor, is determined. Two design strategies are considered. First, an optimal design is intended to achieve the maximum system integrity. System integrity is defined as the balanced contribution of system components to its reliability. To quantify the system integrity, the Integrity Index is defined, and its calculation for various systems is discussed. Second, a designated failure scenario is considered, where some components serve as a fuse to protect some other components. This design strategy is especially applicable to mooring systems with drag anchor foundations because normally, if a drag anchor is pulled out from the seabed, it can cause significant damages to nearby subsea facilities. Using the rules of probability, a method is then developed to calculate the optimality factor of each component. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/149292
The growing interest in the use of offshore platforms in deeper waters and harsher environments, as well as the desire to extend the operation of existing structures beyond their design lives, is increasing attention on the assessment of their dynamic response and their failure conditions under extreme storm loading. There are a large number of factors influencing the performance of dynamically sensitive platforms, but a major issue is how to include all of the irregularity, directionality and nonlinearity that ocean waves cause on their loading. Therefore, the role each plays in the assessment of dynamically sensitive structures under extreme loads is investigated systematically in this thesis. The aim is to develop practical methods to estimate extreme response and the probability of failure of dynamically sensitive offshore structures in a given sea-state. The directionality and nonlinearity of ocean waves has been captured in this thesis by extending the formulations of the NewWave and Constrained NewWave theories. NewWave is a deterministic method that accounts for the spectral composition of the sea-state, and can be used as an alternative to both regular wave and full random time domain simulations of lengthy time histories. Based on this theory a predetermined crest height and the surface elevation around the crest during an extreme event can be theoretically simulated. Constrained NewWave, which is generated by mathematically constraining a NewWave within a random time series, allows the irregularity of ocean waves to be considered. These wave theories have been extended in this thesis to include 2nd order and directionality effects, and their formulations have been written into a new Fortran code for calculation of the water surface and water particle kinematics. The effects of irregularity, directionality and nonlinearity of ocean waves on dynamically sensitive structures are then shown for an example mobile jack-up drilling platform. The sample jack-up platform is modelled in the USFOS software, and includes the effects of material and geometrical nonlinearities as well as spudcan-soil-structure nonlinear interactions. Finally, based on structured application of multiple Constrained NewWaves in combination with the Monte Carlo method, a framework is proposed to estimate the extreme response and the failure probability of dynamically sensitive offshore structures exposed to a given duration of the one extreme sea-state. The results demonstrate that in an extreme event the irregularity, directionality and nonlinearity of ocean waves have considerable effects on the overall performance of the sample jack-up platform. It is shown that the extreme response and the probability of failure of the sample jackup are not only governed by the maximum crest elevation but also depend on the random background of ocean waves. In addition, it is indicated that the inclusion of the directionality effects of ocean waves results in reductions in the extreme response and failure rate of the sample jack-up platform. On the other hand, the nonlinearity effects cause additional energy in low and high frequencies and raise the crest height, which increases the extreme response of the sample jack-up platform. The methods developed in this thesis have application to any dynamically sensitive structure and will help reduce the level of uncertainty in predicting their extreme response or failure probability. This may help in extending their operational conditions, say into deeper waters and harsher sea-states, or in extending their operational life.
Offshore Risk Assessment was the first book to deal with quantified risk assessment (QRA) as applied specifically to offshore installations and operations. Risk assessment techniques have been used for more than three decades in the offshore oil and gas industry, and their use is set to expand increasingly as the industry moves into new areas and faces new challenges in older regions. This updated and expanded third edition has been informed by a major R&D program on offshore risk assessment in Norway and summarizes research from 2006 to the present day. Rooted with a thorough discussion of risk metrics and risk analysis methodology, subsequent chapters are devoted to analytical approaches to escalation, escape, evacuation and rescue analysis of safety and emergency systems. Separate chapters analyze the main hazards of offshore structures: fire, explosion, collision, and falling objects as well as structural and marine hazards. Risk mitigation and control are discussed, as well as an illustration of how the results from quantitative risk assessment studies should be presented. The third second edition has a stronger focus on the use of risk assessment techniques in the operation of offshore installations. Also decommissioning of installations is covered. Not only does Offshore Risk Assessment describe the state of the art of QRA, it also identifies weaknesses and areas that need further development. This new edition also illustrates applications or quantitative risk analysis methodology to offshore petroleum applications. A comprehensive reference for academics and students of marine/offshore risk assessment and management, the book should also be owned by professionals in the industry, contractors, suppliers, consultants and regulatory authorities.
Researchers in the engineering industry and academia are making important advances on reliability-based design and modeling of uncertainty when data is limited. Non deterministic approaches have enabled industries to save billions by reducing design and warranty costs and by improving quality. Considering the lack of comprehensive and defini