Offshore Terminals Research Articles

O PAPEL DA ORGANIZAÇÃO MARÍTIMA INTERNACIONAL NA PROTEÇÃO DO MEIO AMBIENTE MARINHO

Tankers transport liquid cargoes in bulk across the globe, representing a crucial and highly lucrative mode of maritime transport. Given this context, the secure transport of crude oil, derivatives, petrochemicals, and liquefied gases, as well as cargo transfers between inshore, onshore, and offshore terminals, necessitates standardization and effective regulations. In response to a series of oil tanker accidents in 1976-1977, the International Convention for the Prevention of Pollution from Ships (MARPOL) was established, which is the primary international framework for preventing marine pollution. This convention includes regulations aimed at preventing and mitigating pollution from ships, addressing both accidental discharges and routine operational emissions, and is currently supported by six technical annexes. Consequently, ensuring safe operations and environmental protection is a global priority for shipping companies. Researching and promoting this topic serves as a means of disseminating information to users.

Vulnerability assessment of offshore terminals in the Sultanate of Oman: The case of a security audit for SPM Terminal of Mina al Fahal

Nowadays, the pressure for enhanced attention to critical infrastructure security and the focused concern on threats emanating from both domestic and foreign terrorist groups have fostered new challenges for Petrochemical Seaports and Offshore Terminals (PSOTs). These tendencies dictate to maintain comprehensive security regimens that can be integrated with national and international strategies to support the country’s security against terrorism. Therefore, the need for a Security Risk Management (SRM) programme will be an essential part of the business of running a seaport particularly if the addressed port or terminal is handling hazardous chemicals produced from a nearby plant or refinery for export purposes. As a result, by the use of a case study in this paper, the identified security risk factors for an offshore Single Point Mooring (SPM) terminal located inshore side of the seaport of Mina al Fahal in Sultanate of Oman will be assessed by introducing its designated Security Risk Factor Table (SRFT) in order to examine the vulnerability of the addressed terminal. Consequently, the proposed framework can be used by intelligence analysts or port security and risk managers for the protection of these critical infrastructures. Suitable mitigation measures and further treatments for lessening the impact of a successful terrorist attack or potential likelihood of other threats in PSOTs facilities will be studied carefully.

Risk analysis of offshore terminals in the Caspian Sea

Nowadays in offshore industry there are emerging hazards with vague property such as act of terrorism, act of war, unforeseen natural disasters such as tsunami, etc. Therefore industry professionals such as offshore energy insurers, safety engineers and risk managers in order to determine the failure rates and frequencies for the potential hazards where there is no data available, they need to use an appropriate method to overcome this difficulty. Furthermore in conventional risk based analysis models such as when using a fault tree analysis, hazards with vague properties are normally waived and ignored. In other word in previous situations only a traditional probability based fault tree analysis could be implemented. To overcome this shortcoming fuzzy set theory is applied to fault tree analysis to combine the known and unknown data in which the pre-combined result will be determined under a fuzzy environment. This has been fulfilled by integration of a generic bow-tie based risk analysis model into the risk assessment phase of the Risk Management (RM) cycles as a backbone of the phase. For this reason Fault Tree Analysis (FTA) and Event Tree Analysis (ETA) are used to analyse one of the significant risk factors associated in offshore terminals. This process will eventually help the insurers and risk managers in marine and offshore industries to investigate the potential hazards more in detail if there is vagueness. For this purpose a case study of offshore terminal while coinciding with the nature of the Caspian Sea was decided to be examined.

Quantitative risk analysis of loading and offloading liquefied natural gas (LNG) on a floating storage and regasification unit (FSRU)

Natural Gas is becoming an important energy source option and the capacity of the world to produce it is surging. Large reserves of natural gas exist worldwide, particularly in areas where the resources exceed the demand. Therefore, natural gas is liquefied for shipping; and its storage and regasification process usually occurs in onshore facilities. Recently, Liquefied Natural Gas (LNG) offshore terminals have been proposed as an attractive alternative solution. This paper presents a complete quantitative risk analysis (QRA) of undesired events that may occur during the loading and unloading of Liquefied Natural Gas (LNG) considering a typical LNG carrier and an offshore terminal similar to those operating in Brazil. Initially, a historical survey of accidents at LNG facilities, along with a detailed study of LNG carriers and LNG offshore terminals, is presented to support hazard identification. Once the potential hazardous events are categorized in some possible scenarios, a probabilistic potential hazard assessment is performed; moreover, the frequencies of occurrence of the undesired events are estimated. Afterwards, traditional consequence models are briefly discussed aiming to identify the weakness of each one that supports the specification of the model used in the consequence analysis of a specified case, which is evaluated by providing the data to estimate the total risk of the installation. The risk is evaluated in terms of social and individual risk. Lastly, possible control measures able to reduce the frequency of occurrence, or mitigate the impacts associated with the analyzed scenarios, are proposed and new risks levels are estimated by considering those control measures. The paper presents a complete QRA, presenting the tools and the models chosen to perform the analysis as well as some of the advantages and limitations regarding the use of these tools and models.

An experimental study of the wave excitation in the gap between two closely spaced bodies, with implications for LNG offloading

The side-by-side offloading of liquid natural gas (LNG) at offshore terminals involves a fixed and a floating body in close proximity; the offshore terminal being the fixed body and the LNG tanker the floating body. The closeness of the two bodies leads to the formation of a long and relatively narrow gap, within which there is the potential for large amplifications of the water surface elevation. The present paper uses experimental results to characterise both the size and nature of the excitation within the gap. It also illustrates the effect of the vessel motion on this amplification by considering a 1:100 scaled model of an LNG tanker as well as its fixed approximation. It is found that the body's ability to move acts to increase the frequency at which resonant amplification within the gap occurs (the resonance frequency). The incident wave conditions considered include regular and irregular waves in both beam- and head-sea orientations; the latter leading to very different gap end conditions. The nature of the resonant amplification for the floating LNG tanker is shown to be similar for the two orientations, suggesting that the gap end conditions do not drive the resonant amplification. Consideration of the nonlinearity within the gap illustrates that resonant amplification occurs at the resonance frequency, irrespective of whether the fluid motion is first or second harmonic. The present paper provides data relevant to the safe offloading operations of an LNG tanker and demonstrates the importance of incorporating the vessel motion in numerical modelling procedures.

Evaluation of the PRICO liquefaction process using exergy-based methods

The PRICO process is a single mixed-refrigerant process used for small-scale LNG plants, including offshore terminals. The working fluid (refrigerant) is a mixture of methane, ethane, butane and nitrogen. The behavior of the mixture in processes such as cooling, heating, compression, evaporation and condensation depends on its composition and on the part of the chemical constituents of the mixture that are in the gas and liquid phases. The state-of-the art for the evaluation and optimization of the PRICO process is discussed. Exergy-based analyses, i.e. exergetic, exergoeconomic and exergoenvironmental analyses, are applied to the evaluation of the PRICO liquefaction process of natural gas. The purpose of the paper is to identify options for improving the PRICO process and to demonstrate the application of exergy-based methods to the improvement of an LNG plant. The perspectives from the thermodynamic, economic and environmental impact points of view are discussed.

浮体を用いたLNG タンクのスロッシング防止に関する研究

Recent developments with offshore terminals and floating liquefied natural gas (FLNG) production, storage and offloading applications have included the new requirement that the storage tanks be able to handle unrestricted filling with LNG. If membrane-type tanks are used in such new systems, the occurrence of sloshing in the half-load condition becomes one of the most important design issues. In this paper, the authors propose a simple anti-sloshing floating device to be installed inside a liquid cargo tank. By setting the device on the free surface of the liquid cargo, the original free surface is divided into two or more sub-surfaces, and resonant sloshing of the liquid can be avoided by changing the natural frequency of its motion. This floating device can follow the liquid height change in the tank during loading and unloading operations of the liquid cargo, a feature that is especially preferable in FLNG applications. The authors examine the performance of the proposed anti-sloshing device by a series of model experiments and numerical simulations, which indicate that the device's performance is very promising.

First step in optimizing LNG storages for offshore terminals

The development of new LNG offshore facilities addresses new technical challenges that need to be deeply investigated to overcome the new constraints raised from the offshore operability. One of the key issues concerns the management of LNG storages. As future offshore LNG projects could be implemented in areas with harsh environmental conditions, the motions of the floating structure combined to the design and operating parameters should widely affect the behavior of the LNG inside partially filled tanks. Therefore, the knowledge available from onshore LNG storages has to be completed taking into account the offshore environment. The first concern deals with the production of Boil-Off Gas (BOG) during LNG’s unloading and storage operations under offshore conditions, where specific offshore parameters would contribute in increasing the production of BOG. For that purpose, a new optimized LNG storage process based on an increased operating pressure ( P = 500 mbarg) in the TRITON FSRU’s tanks has been investigated during LNG’s unloading and storage operations with LNG emission. It mainly showed that by operating at 500 mbarg, the production of BOG is nearly 4 times reduced during unloading operations compared to LNG carrier standard operating pressure (100 mbarg) and nearly suppressed during the storage phase. The second concern deals with managing the rollover risk under offshore conditions. In this context, GDF SUEZ performed a pioneer qualitative assessment to highlight the impact of the liquid motion on the rollover mechanisms in the TRITON FSRU’s tanks. The liquid motion completely modifies the mixing mechanisms in LNG stratified layers. The mixing is no longer governed by the molecular diffusion induced by the thermal effects but by the dynamic flow effects induced by the fluid wave movement into the layers. Moreover, this assessment showed that the time needed for a stratification to evolve up to a complete mix is severely reduced compared to the onshore LNG storage while the assessment of the induced BOG peak depends as usual on the energy stored in the stratification when being mixed and could be of the same order of magnitude as for onshore rollover.

Application of a generic bow-tie based risk analysis framework on risk management of sea ports and offshore terminals

Ports and offshore terminals are critical infrastructure resources and play key roles in the transportation of goods and people. With more than 80 percent of international trade by volume being carried out by sea, ports and offshore terminals are vital for seaborne trade and international commerce. Furthermore in today's uncertain and complex environment there is a need to analyse the participated risk factors in order to prioritise protective measures in these critically logistics infrastructures. As a result of this study is carried out to support the risk assessment phase of the proposed Risk Management (RM) framework used for the purpose of sea ports and offshore terminals operations and management (PTOM). This has been fulfilled by integration of a generic bow-tie based risk analysis framework into the risk assessment phase as a backbone of the phase. For this reason Fault Tree Analysis (FTA) and Event Tree Analysis (ETA) are used to analyse the risk factors associated within the PTOM. This process will eventually help the port professionals and port risk managers to investigate the identified risk factors more in detail. In order to deal with vagueness of the data Fuzzy Set Theory (FST) and possibility approach are used to overcome the disadvantages of the conventional probability based approaches.

Gas on the Water

This article highlights the race to bring liquefied natural gas (LNG) onto America’s continental shelf. The new LNG tanker Excelsior moored to the underwater buoy of Excelerate Energy’s Energy Bridge and, after receiving a Coast Guard go-ahead, began re-gasifying its contents and injecting them into the nation's pipeline grid. Energy Bridge tops a list of nearly a dozen offshore terminals in various stages of planning or construction. It joined an even longer list of LNG terminals in various phases of planning or construction trying to do the same thing on land. Offshore terminals will play a role in this total, as Energy Bridge is demonstrating. Placing terminals at sea eliminates some of the concern about transporting LNG near or through populated coastal regions.

Integrating Geologic and Economic Data Using a Geographic Information System (GIS): Offshore Gulf of Mexico

A comprehensive data base consisting of graphical elements with associated attribute values has been compiled for the Gulf of Mexico. These geographically registered data, obtained from federal, state, third party, and company sources, consist of economic, past and present hydrocarbon production, and geologic information. Data representing man-made features such as pipelines, offshore drilling structures, terminals, and ship channels were evaluated with water depth and coastline proximity to estimate cost/risk factors of oil exploration and production. Hard production data and soft data including estimates of oil maturity, undiscovered hydrocarbons, fault timing, and time of oil generation were likewise geographically registered with federal and state lease blocks. All attribute data were compiled at the well, field, and tract level in a company-standard relational data base for estimation of play boundaries, recoverable reserves, and valuation of bid strategies. Conventional 2-D GIS technology in a relational environment enhances the evaluation of available data for assessing hydrocarbon potential on a unit by unit basis. These analyses provide the input for true 3-D reservoir evaluation in the geological sense and with registered economic data, provide cost versus return estimates for any 3-D volume, given some known error.

Influence of wave board type on bounded long waves

The long wave energy attached to the grouping of natural waves has been shown to play a very important role in the design of mooring systems, offshore terminals, floating structures, harbours, etc. Therefore, in model testing, efforts should be made to reproduce only the correct amount of long wave energy present in nature. However, when only traditional first-order control signals are applied to the wave generator errors will be introduced. Hence, a second-order signal has to be calculated and imposed in order to obtain satisfactory long wave conditions in the physical model. The necessary signal and transfer functions are outlined below for all common types of wave boards. It is demonstrated that dependent on the type (piston, hinged, etc.) considerable differences can be found in the amplitude of the required second-order control signal. Also the erroneous longwave energy is assessed in case of only first-order wave generation. The results indicate that in such situations significant deviations from th...

The Action of Irregular Waves on Ships Moored on Terminals

For the analysis of the dynamic characteristics of ships moored at the offshore terminals under the action of wind waves, the moored ship system may be simplified to be linear. Introducing the transfer function Ye(ω), the impact energy of a moored ship on the terminal resulting from a random sea may be obtained from the spectrum of the ocean waves. Furthermore, by using the directional function of impact Y2(α), the directional spectrum of the impact by ships can also be estimated. The results show that there is a significant relationship between the spectrum of the ocean waves and the impact energy of the ship.

Long Wave Problems in Laboratory Models

For the design of harbors, offshore terminals, floating platforms, etc. it is of great importance that the long waves in nature are correctly represented in the physical model, because of the dominant influence of the long waves on mooring forces and slow-drift oscillations. Mostly, the long waves are a function of the grouping of wind waves. The present second order wave generation analysis reveals several long wave terms of practical interest. Various terms dominate in different frequency ranges, and this influences the control of the wave generators. For practical purposes a simple procedure for estimating the group-induced long waves and the necessary amplitude of the generator piston is proposed. These quantities are obviously important for the choice of model scale, since the practical limits of piston stroke, resolution, water depth, etc. must be observed. The long wave errors in traditional model tests with only first order wave generation are investigated. In shallow water model tests the long wave effect tends to be underestimated, while it is exaggerated in deep water tests.

High-Amplitude Low-Cycle Fatigue in Concrete Sea Structures

F ourteen prestressed concrete structures are now in service as oil drilling, production, and storage platforms in the North Sea. Other fixed concrete structures are in service as offshore terminals, floating docks, floating terminals, breakwaters, and floating bridges in many parts of the world. These structures will typically be subjected to 2 x 108 cycles of waves during a normal service lifetime. At the same time, concepts are being developed for concrete structures in the Arctic regions, where they may be subjected to many extended periods of continuous crushing of sheet ice. One such structure, the Dome Petroleum's Tarsiut caisson-retained island, is currently under construction in the Canadian Beaufort Sea. Such ice crushing may have a frequency of peak force development similar to the natural period of the structure.' If continuous crushing is assumed to act in one direction for 25 percent of the time over an ice regime lasting 4 months per year, such a structure could experience 107 cycles in a 50-year lifetime. In the case of waves, a probable long-term history of expected loadings can be developed, from which the stress ranges versus number of cycles (S-N curves) can be computed. In the case of Arctic ice, the distribution of ridges in the sheet and the forces and stresses acting on the structure are less well determined; however, a Poisson distribution appears probable 2 with relatively few large events interspersed among a large number of moderate and low cycles (see Fig. 1). The typical concrete sea structure, such as those in the North Sea, is so

Structural Design of Production Risers and Offshore Production Terminals

Offshore production terminals and deepwater risers are seeing increasing use by the offshore oil industry. The structural design of these units presents a unique challenge compared to other offshore systems. Development of design loading conditions and fatigue histories is especially interesting due to the complex interaction of nonlinear riser and vessel dynamics, the statistical nature of maximum loads and the need to consider directionality as well as the magnitude of environmental loading. This paper presents a complete procedure for predicting design loads and fatigue histories for production risers and offshore terminals. The emphasis will be on systems wherein a dedicated vessel is connected to the riser by a rigid mooring arm. A number of structural design configurations will be surveyed. Techniques for preliminary sizing, dynamic analysis, model testing and fatigue analysis will be discussed. The application of this procedure to several specific design cases will be summarized.

The Surveying Requirements for Deep-Draught Routes

Less than a third of the world’s continental shelves has been surveyed by echo sounder, the rest, if surveyed at all, has been covered only by hand-lead and line. Large rocks and wrecks undoubtedly lie undetected between individual casts of the lead and even between quite modern echo sounding profiles. The draught of merchant ships has doubled since the 1960s. Minimal underkeel clearances are now accepted and many new routes are being used across the continental shelves between offshore energy exploitation platforms and new shore terminals. Examples are given of typical shelf surveys and of various ways of meeting modern requirements, including the use of multiple echo sounders, sidescan sonars and sector scanning sonars. Reference is made to the effects on charting of the increasing amount of data available on individual wrecks and seabed obstructions as well as the use of traffic separation schemes. Attention is drawn to the need to monitor the depth in unstable seabed areas, the effect of negative surges and the need for source-data diagrams on charts.

Underwater inspection/testing/ monitoring of offshore structures

The extraction of offshore oil and gas deposits has resulted in installation of massive steel and concrete platforms in progressively deeper and more hostile waters. Concern for the safety of platform personnel, potential damage to the environment, and the assurance of profitable, unimpeded, extraction of these offshore resources is a concern of host-country governments and the offshore operators. Requirements for underwater inspection of these structures and the techniques and tools to conduct such inspection vary widely from country-to-country. In some instances periodic inspection is required by law; in other instances there is no requirement whatever once the structure has been installed. The instruments to conduct underwater inspections also vary; their effectiveness is sometimes questionable, and the cost of underwater inspection to the operator (which will eventually be borne by the consumer) is high and will get higher as the water depth and complexity of the structure increases. The purpose of this six month study was: 1) to identify and describe all actual or potential underwater inspection requirements (national and international) for fixed concrete and steel structures promulgated by the governments of offshore oil and gas producing countries and by the offshore operators themselves; 2) to identify and assess the state-of-the-art in underwater non-destructive testing/monitoring/inspection of offshore structures; 3) to evaluate the capability of servicing and hardware producers to meet the inspection requirements identified; and 4) to describe and establish priorities for specific tasks for technology development that should be undertaken to satisfy current and future requirements. While this study concentrates on fixed offshore oil and gas structures, the results also reflect the state-of-the-art in underwater inspection/testing for other offshore structures as well, e.g., floating power platforms; offshore terminals and deepwater ports. The data for this study were collected in three stages. First, an intensive literature review was conducted to initially identify those organizations and governments active in projects related to the study goals (the results of this literature survey are presented in Appendix I). Second, telephone interviews were conducted to further identify “Requirements” sources and suppliers/manufacturers of inspection/testing capabilities in the U.S. and Europe. Third, personal interviews were conducted with individuals active in hardware production or inspection services. Personnel and organizations contacted (both by telephone and on a personal basis) are identified in Appendix II (Requirements) and III (Capabilities), respectively. Approximately four months were required to satisfy the data collection phase; the remaining two months were spent analyzing, reducing and synthesizing the data obtained.

Offshore subsea engineering

As a result of years of research and development work on subsea completions, manifolds and flowlines, followed by field installations in relatively shallow and calm waters, a number of well completion and flowline laying and connecting methods are available and operational. The installation methods are basically diverless and control and maintenance are achieved by sophisticated systems; likewise the floating offshore terminals such as the E.L.S.B.M. and the Spar have been designed, built and put into operation. Although these systems were meant to be installed mainly in deeper waters, say beyond 210 m where diver access and the use of conventional techniques would become rather limited for technical and economic reasons, it is now evident that many fields in shallower waters can be more economically and efficiently developed or complemented by the use of deepwater techniques. Current development work concentrates on the design and evaluation of multibore production risers, floating production platforms and pipelaying and repair.

MODEL TESTS WITH DIRECTLY REPRODUCED NATURE WAVE TRAINS

Hydraulic model tests are still recognized as the best and in many cases the only tool, indeed, for investigations of design criteria for harbours concerning a) the effect of wave disturbance on moored ships in harbour basins and at offshore terminals, b) stability of structures and wave forces on structures. Model tests with waves have until recently usually been made with regular waves varying the wave height, wave period, wave direction for each test run. An important improvement in the model technique has been the development of irregular wave generators, capable of generating waves directly from nature wave records. The following aspects are presented below 1) A discussion on the methodology of wave model tests. 2) A method for direct reproduction of nature wave records. 3) A method for determining the incoming wave heights in a short wave flume with a reflecting structure and reflection from the wave generator paddle.