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This paper investigates the operating benefits and limitations of utilizing carbon dioxide in hydro-pneumatic energy storage systems, a form of compressed gas energy storage technology, when the systems are deployed offshore. Allowing the carbon dioxide to transition into a two-phase fluid will improve the storage density for long-duration energy storage. A preliminary comparative study between an air-based and a carbon dioxide-based subsea hydro-pneumatic energy storage system is first presented. The analysis is based on thermodynamic calculations assuming ideal isothermal conditions to quantify the potential augmentation in energy storage capacity for a given volume of pressure containment when operating with carbon dioxide in lieu of air. This is followed by a transient thermal analysis of the carbon dioxide-based hydro-pneumatic energy storage system, taking into account the real scenario of a finite thermal resistance for heat exchange between the gas and the surrounding seawater. Results from numerical modelling revealed that the energy storage capacity of a carbon dioxide-based subsea hydro-pneumatic energy storage system operating under ideal isothermal conditions can be theoretically increased by a factor of 2.17 compared to an identical air-based solution. The numerical modelling revealed that, under real conditions under which transient effects resulting from a finite thermal resistance are accounted for, the achievable factor is lower, depending on the charging and discharging time, the initial temperature, and whether a polyethene liner for corrosion prevention is considered or not. [ABSTRACT FROM AUTHOR]

This paper investigates the operating benefits and limitations of utilizing carbon dioxide in hydro-pneumatic energy storage systems, a form of compressed gas energy storage technology, when the systems are deployed offshore. Allowing the carbon dioxide to transition into a two-phase fluid will improve the storage density for long-duration energy storage. A preliminary comparative study between an air-based and a carbon dioxide-based subsea hydro-pneumatic energy storage system is first presented. The analysis is based on thermodynamic calculations assuming ideal isothermal conditions to quantify the potential augmentation in energy storage capacity for a given volume of pressure containment when operating with carbon dioxide in lieu of air. This is followed by a transient thermal analysis of the carbon dioxide-based hydro-pneumatic energy storage system, taking into account the real scenario of a finite thermal resistance for heat exchange between the gas and the surrounding seawater. Results from numerical modelling revealed that the energy storage capacity of a carbon dioxide-based subsea hydro-pneumatic energy storage system operating under ideal isothermal conditions can be theoretically increased by a factor of 2.17 compared to an identical air-based solution. The numerical modelling revealed that, under real conditions under which transient effects resulting from a finite thermal resistance are accounted for, the achievable factor is lower, depending on the charging and discharging time, the initial temperature, and whether a polyethene liner for corrosion prevention is considered or not.

In this study, the pressure compensation mechanism of a reducer bellows is analyzed. This device is typically used to reduce the size of undersea instruments and improve related pressure resistance and sealing capabilities. Here, its axial stiffness is studied through a multi-fold approach based on theory, simulations and experiments. The results indicate that the mechanical strength of the reducer bellows, together with the oil volume and temperature are the main factors influencing its performances. In particular, the wall thickness, wave number, middle distance, and wave height are the most influential parameters. For a certain type of reducer bellows, the compensation capacity attains a maximum when the wave number ratio is between 6:6 and 8:4, the wall thickness is 0.3 mm, and the wave height is between 4-5 mm and 5-6 mm. Moreover, the maximum allowable ambient pressure of the optimized reducer bellows can reach 62.6 MPa without failure, and the maximum working water depth is 6284 m. [ABSTRACT FROM AUTHOR]

Traditionally, subsea pipelines designed for the transportation of oil, gas, and water are constructed using carbon steel due to its strength, toughness, and ability to operate at temperatures up to 427 °C. However, polyethylene (PE), especially its high-density variant (HDPE), presents advantages such as reduced installation costs, diminished water leakage, and superior corrosion resistance. As research endeavours to enhance PE properties, its adoption for subsea applications is anticipated to rise. This study first delineates the mechanical behaviour of HDPE pipelines for offshore installation, identifying pulling tension, dimension ratio, water depth, and air fill ratio as the paramount lay parameters. Subsequently, a theoretical bend radius equation was derived from pipelaying mechanics using a purely geometric approach. Within this equation, two determinants, parameter X and parameter Y, dictate the sagbend bend radius. Regression analysis elucidated the relationships of lay parameters with both X and Y, yielding a general equation for X in terms of pull tension, water depth, and air fill ratio and another for Y as a function of water depth. Together, these geometric determinants underpin the sagbend bend radius estimation model. For overbend bend radius prediction, a lay index (IL) was fashioned from the aforementioned three parameters. Correlation assessments between the lay index and overbend bend radius revealed R2 values of 0.940, 0.836, and 0.712 for pipes with diameters of 2.0, 2.5, and 3.0 metres, respectively. This underscores the model's proficiency in predicting the bend radius, albeit with decreasing precision for larger-diameter pipelines. [ABSTRACT FROM AUTHOR]

To avoid the impact of marine environmental loads such as wind, wave and current, mud line low temperature on drilling and completion operation string and production string, offshore pipe-in-pipe structure was widely used for its good safety protection, thermal insulation, transmission and other properties. At present, the mechanics, strength and safety analysis of pipe-in-pipe(PIP) were mainly based on single pipe structure. In order to systematically sort out the mechanical analysis method of PIP during operation, firstly, the structural composition of PIP, the internal pressure, external pressure and buckling design and verification analysis methods of offshore single pipe were introduced. Then, according to the characteristics of horizontal collapse of offshore pipe string, the main four collapse modes and the calculation method of collapse transmission pressure of PIP were explained based on the single pipe collapse and its propagation formula. Finally, on the basis of summarizing the theory and results of PIP dynamic analysis, the development direction of PIP structural dynamics was put forward. The study is helpful to the in-depth study of structural mechanics of offshore PIP, and can provide reference for the safe operation of PIP in deep water in China. [ABSTRACT FROM AUTHOR]

Decisive steps in innovation and competitiveness are needed to meet global greenhouse gas emissions and climate goals. As an effective method for reducing carbon emissions, carbon dioxide (CO2) storage and utilization on the seabed enable the transport of captured CO2 via pipelines or ships to permanent storage sites, such as saline aquifers or depleted oil and gas reservoirs in subsea sediments, or by injecting CO2 for the replacement and displacement of subsea resources (oil, gas, gas hydrates, etc.). Subsea CO2 utilization and storage (SCUS) involves several research hotspots worldwide, including international and local laws and regulations, security, economics, environmental impact, and public acceptance. Its current research and engineering progress are also of great interest. In addition, the vigorous implementation of the energy transition and the rapid development of renewable energy sources globally have resulted in significant advancements in SCUS. This paper provides an overview of carbon dioxide storage and utilization mechanism in the seabed, analyzes key technical and economic issues, and summarizes existing research on safety risks, monitoring technologies, and investment and operating cost control to identify remaining knowledge gaps. This is followed by an overview of global engineering practice to update on current progress. Finally, combined with the actualities of China, the potential and trend of China's seabed carbon storage and utilization are summarized. This review demonstrates the enormous development prospects for seabed carbon storage and utilization, although some risks remain including leakage and contamination, with which innovation in monitoring technologies and the self-sealing effect of gas hydrate, safe subsea utilization and storage of CO2 can be achieved. Additionally, considering the development of renewable energy and the demand for large-scale energy storage, hydrogen, ammonia, or other energy carriers and carbon dioxide storage and utilization can be coupled into an industrial chain to form an economically competitive carbon geological storage mode.

Recently, large offshore wind power plants have been installed far from the shore, using long HVAC three-core armored cables to export power. Its high capacitance may contribute to the appearance of unwanted phenomena, such as overvoltages or resonances at low frequencies. To adequately assess these problems, detailed and reliable cable models are required to develop time-domain/frequency-domain analyses on this type of cables. This paper presents, for the first time in the literature, an assessment on the performance of 3D finite element method-based (3D-FEM) models for developing frequency-domain analyses on three-core armored cables, confronting simulation results with experimental measurements found in the literature for three real cables. To this aim, a simplified ultra-shortened 3D-FEM model is proposed to reduce the simulation time during frequency sweeps, through which relevant aspects never analyzed before with frequency-domain 3D-FEM simulations are addressed, such as total losses, induced sheath current, magnetic field around the power cable, positive and zero sequence harmonic impedances, as well as resonant frequencies. Also, a time-domain example derived from the frequency-domain analysis is provided. Remarkable results are obtained when comparing computed values and measurements, presenting the simplified ultra-shortened 3D-FEM model as a valuable tool for the frequency-domain analysis of these cables. [ABSTRACT FROM AUTHOR]

Traditionally, subsea pipelines designed for the transportation of oil, gas, and water are constructed using carbon steel due to its strength, toughness, and ability to operate at temperatures up to 427 °C. However, polyethylene (PE), especially its high-density variant (HDPE), presents advantages such as reduced installation costs, diminished water leakage, and superior corrosion resistance. As research endeavours to enhance PE properties, its adoption for subsea applications is anticipated to rise. This study first delineates the mechanical behaviour of HDPE pipelines for offshore installation, identifying pulling tension, dimension ratio, water depth, and air fill ratio as the paramount lay parameters. Subsequently, a theoretical bend radius equation was derived from pipelaying mechanics using a purely geometric approach. Within this equation, two determinants, parameter X and parameter Y, dictate the sagbend bend radius. Regression analysis elucidated the relationships of lay parameters with both X and Y, yielding a general equation for X in terms of pull tension, water depth, and air fill ratio and another for Y as a function of water depth. Together, these geometric determinants underpin the sagbend bend radius estimation model. For overbend bend radius prediction, a lay index (IL) was fashioned from the aforementioned three parameters. Correlation assessments between the lay index and overbend bend radius revealed R2 values of 0.940, 0.836, and 0.712 for pipes with diameters of 2.0, 2.5, and 3.0 metres, respectively. This underscores the model’s proficiency in predicting the bend radius, albeit with decreasing precision for larger-diameter pipelines.

Slugging flow is a condition caused by a liquid obstruction at the riser base. It exhibits cyclic behaviour. The cycle consists of a protracted time of no gas production at the riser's top, followed by the arrival of a liquid slug with a length greater than the riser height, and ultimately the breakthrough of a significant gas surge. The cycle time might range from a few minutes to a few hours, depending on the system size and flow conditions. In offshore oil production, feedback control is a practical and cost-effective way to prevent slug flow. To control the flow rate or the pressure in the pipeline, adjusting the choke valve opening on the topside facility is generally utilised as the control input. From a practical standpoint, designing a control system based on topside data rather than seabed measurements is preferable. Controlling the topside pressure alone is difficult and ineffective in reality, but combining it with the flow rate results in a more reliable control solution. Measuring the flow rate of a multiphase flow, on the other hand, is difficult and expensive. All the topside measurements-based slug control techniques was critically reviewed and necessary recommendations for enhanced control performance provided. In conclusion, this review acknowledged that slugging is a well-defined flow pattern, yet despite having been studied for several decades, current slug control methods still have robustness issues. Slug flow problems are expected to become even more intense in the future as a result of longer vertical risers driven by deep-water Exploration and Production (E&P).

The integration of a magnetic gear (MG) and permanent magnet machine to realize a torque dense, hermetically sealed, low maintenance subsea propulsion thruster is investigated. An MG element with an airgap shear stress more than 140 kPa was developed and manufactured. The careful selection of design parameters enabled the hermetically sealed magnetically geared thruster to achieve more than 90% efficiency at its peak power requirement. [ABSTRACT FROM AUTHOR]

Subsea valves and actuators are typically installed at very deep-water depths between 1 and 3 km. The seawater column at such depths applies a high amount of pressure on subsea valves and actuators. Therefore, one way to make sure that subsea equipment and components can withstand the tremendous external pressure of the seawater is to make the component wall thick enough, as is the practice for subsea valves. Subsea actuators, unlike valves, are not designed thick enough since actuators shells are not pressurized by internal fluid. The alternative solution to prevent the implosion and failure of actuators due to seawater pressure head, and to avoid increasing material cost by increasing wall thickness, is to use a pressure balance compensation system. The main research question is twofold: how to select between the available compensation systems in the industrial world and how to implement conceptual design for the selected compensation system. The research does not include a detailed design of the compensation system. The spring type pressure compensation system is reviewed in this paper and is not recommended due to the possibility of spring damage due to high cycling load. Installing the pressure compensation on the surface and connecting the compensation oil fluid to the subsea equipment through piping or tubing is more costly, less efficient and heavier compared to a bladder type compensation system. Bladder type compensation, also known as closed compensation, is widely used for subsea actuators as an environmentally friendly solution. This paper proposes a conceptual design for this type of compensation system that includes a wall thickness calculation according to American Society of Mechanical Engineers Sec. VIII Div. 02 requirements, as well as pressure relief valves installed on the compensation system according to American Petroleum Institute (API) 526 requirements. [ABSTRACT FROM AUTHOR]

The response of permafrost to marine submergence can vary between ice‐rich late Pleistocene deposits and the thermokarst basins that thawed out during the Holocene. We hypothesize that inundated Alases offshore thaw faster than submerged Yedoma. To test this hypothesis, we estimated depths to the top of ice‐bearing permafrost offshore of the Bykovsky Peninsula in northeastern Siberia using electrical resistivity surveys. The surveys traversed submerged lagoon deposits, drained and refrozen Alas deposits, and undisturbed Yedoma from the coastline to 373 m offshore. While the permafrost degradation rates of the submerged Yedoma were in the range of similar sites, the submerged Alas permafrost degradation rates were up to 170% faster. Remote sensing analyses suggest that 54% of lagoons wider than 500 m along northeast Siberian and northwest American coasts originated in thermokarst basins. Given the abundance of thermokarst basins and lakes along parts of the Arctic coastline, their effect on subsea permafrost degradation must be similarly prevalent. Plain Language Summary: Permafrost is defined as any ground or rock colder than 0°C for two or more consecutive years. In unglaciated regions of Siberia during the last ice age, the ground froze 1 km deep. When the ice sheets and glaciers melted at the end of the last Ice Age, millions of square kilometers of this cold permafrost were inundated with seawater on shallow Arctic shelves, creating subsea permafrost. Even today, new permafrost is submerged because of coastal erosion. Once submerged, heat and salt flow thaw the permafrost. However, the rate of subsea permafrost thaw partially depends on its temperature, ice content, and sediment type. Some permafrost areas called Alases already experienced deep thaw and refreezing from Arctic lake formation and drainage. On the southern coastline of the Bykovsky Peninsula in Siberia, we carried out non‐invasive marine geophysical surveys parallel to the coastline to estimate how fast permafrost thaws beneath a submerged Alas next to a lagoon and permafrost areas without Alases. We discovered that subsea permafrost degradation was up to 170% faster beneath the submerged Alas nearshore. To highlight the broader relevance of these Alas‐lagoon landscapes along the Arctic coastline, we map out Arctic lagoons. Key Points: Subsea permafrost degradation was up to 170% faster below submerged thermokarst basins compared to submerged Yedoma remnants nearshoreRe‐worked permafrost beneath thermokarst basins adjacent to lagoons induces rapid offshore thawAlong the assessed Arctic coastline, 54% of lagoons originated in thermokarst basins [ABSTRACT FROM AUTHOR]

Due to recent failures of high‐strength steel bolts that were assembled in the splash zone and the submerged zone of offshore structures, the applicability of European steel construction standards regarding subsea use was investigated. It was found, that Eurocode 3 and EN 1090‐2 do not cover specific requirements for the installation of bolts under water. The influence of water on tightening, bolt preload and slip factor of faying surfaces were examined using special testing equipment. Different tightening me‐thods and alternative washer systems were applied. Lubrication of bolts used according to the standards mentioned does not seem suitable for underwater application. Self‐loosening and bolt overload are potential risks that come with under water installation of corresponding bolt assemblies. Design surface class of faying surfaces could be verified under water, but failure behavior was different when tested under water compared to regular testing conditions. [ABSTRACT FROM AUTHOR]

Hydraulic systems provide a clean and stable supply of hydraulic fluid for subsea valves and actuators installed on the subsea bed in subsea production systems. Subsea control systems are used for contemporary subsea fields instead of installing the control system on topside. Although all-electric subsea systems are state-of-the-art with benefits such as health, safety, and environment improvement, as well as efficiency and lower cost, hydraulic systems are still used for the development of many subsea fields. One of the main questions in the selection of a subsea hydraulic field is whether to choose an open or closed loop hydraulic system. The main characteristic of an open loop hydraulic system is that the hydraulic fluid is discharged into the marine environment during the actuation of the subsea valves. Conversely, the hydraulic fluid is returned to the topside facilities through an umbilical system in a closed loop system. Given that closed loop systems are more eco-friendly, the main question in this research is to examine the effect of the actuator connection of the closed loop system on actuator design. Two cases of actuated valves connected to a closed loop system are analyzed in this paper. The first is a 71/16-in. subsea slab gate valve in the pressure class of 517 bar with a linear spring return fail-safe close (FSC) actuator located on a manifold branch. The data indicates that the piston rod and cylinder diameter of the FSC linear actuator should be increased by some millimeters due to the accumulation of hydraulic oil at the bottom of the actuator. The hydraulic oil in the closed loop system helps in closing the actuator and spring force, so the spring constant and torque should be reduced as a result. The second case involves a 16-in. subsea ball valve in the pressure class of 517 bar with a double-acting fail-as-is rack and pinion actuator. The conclusion in this case is to avoid making any change in the design of double-acting actuator in connection to the closed loop system. [ABSTRACT FROM AUTHOR]

Information on the contribution of offshore oil and gas (O&G) platforms to fish productivity is required to contribute to the decision-making process to remove, partially remove, or retain these structures during decommissioning after petroleum production ceases. The present study assesses the biomass and fish production of one common and abundant fish species (Caesioperca lepidoptera – butterfly perch) and two commercially fished species (Helicolenus percoides – reef ocean perch; Nemadactylus macropterus – jackass morwong) on eight O&G platforms and in surrounding natural habitats in the Bass Strait, south-east Australia, where options for decommissioning are being assessed. High-definition stereo-video imagery was collected by remotely operated vehicle (ROV) from eight platform facilities, their immediate benthic surrounds, reference areas reflective of the likely pre-installation seabed state (sand-dominated) and a nearby natural 'reef' area referred to as south-east reef (some limestone foundation). The biomass of all three species was low in the benthic surrounds of platforms, at reference locations and at south-east reef where minimal cover by benthic organisms was recorded and, as such, there was little to no fish production for the three study species in these areas. We observed a total fish biomass of 2.85 tonnes across the eight platforms for the three fish species surveyed, with high variability across platforms. Total production (P) across all platforms was estimated at 1244 kg/year for the three species, with a mean fish production density of 82 g/m2/year. Approximately 79% of total production is considered 'new' production (984 kg/year i.e., the production attributed to the presence of the platforms; with a mean production density of 64 g/m2/year). The remaining 21% could be retained or redistributed into the surrounding area if platforms were removed. C. lepidoptera accounted for the majority (90%) of biomass and of total production for all three species across all locations surveyed. Despite only accounting for a small proportion of platform surface area, the bottom 5 m sections of platforms had 41% of the total biomass observed and accounted for 46% of total production of these three study species. Production measures for platforms surveyed here are relatively high compared to other artificial reefs and habitats around the world. Total removal of these platforms will likely result in a reduction of fish biomass and fish productivity (incl. several fishery species) in the immediate vicinity. • Platforms promote fish diversity and abundance in areas where it would be otherwise be minimal. • Platform production measures were relatively high compared to other artificial reefs and habitats around the world. • The bottom 5 m sections of platforms contained 41% of the total biomass observed and accounted for 46% of total production. • Complete removal of infrastructure would likely eliminate most fish production at that location. [ABSTRACT FROM AUTHOR]

Valve failure is a big risk and a costly phenomenon in the offshore sector of the oil and gas industry. It results in severe negative consequences such as loss of asset; loss of production due to plant shutdown; health, safety and environmental (HSE) issues such as hydrocarbon (oil and gas) spillage; environmental pollution; and sometimes loss of human life. Different types of valve failures have occurred in the Norwegian offshore industry for various reasons such as poor material selection, corrosion, mechanical failure of valve components due to high stresses and loads, lack of coating and lack of inspection. The aim of this paper is to review and critique some of the wrong material selection approaches for industrial valves in the offshore sector of the oil and gas industry that lead to the corrosion and failure of valves, and to provide an appropriate material selection solution to mitigate these failures. Seven cases of material failures due to corrosion, including a valve gear box in coated cast iron, bolting made of low alloy steel with hot dip galvanized coating, a stem key made of a low alloy steel, stem material in 17-4 PH, spring material in Inconel X750, duplex, super duplex and hard nickel alloys in subsea as well as graphite packing in seawater, are reviewed, and preventive measures are proposed to avoid corrosion risk. In general, the use of carbon and low alloy steel for valves in the offshore environment should be limited and the use of corrosion-resistant alloys (CRAs) is proposed. [ABSTRACT FROM AUTHOR]

Despite the abundance of telemetric applications for ecology, behaviour and physiology of marine life, few efforts were reported about the use of acoustic telemetry for SCUBA divers. Such systems are required to follow the medical conditions of divers with chronic health problems such as diabetics. This study communicates the details of a study to design, manufacture and test a prototype system that measures the blood glucose while diving and transmit the results in real time to the surface. A subcutaneous glucose sensor placed on the diver transmits wirelessly the glycaemia data to a microcontroller based RF receiver board placed in a custom built waterproof casing. This board works as a relay to transmit the blood glucose value to an acoustic modem SAM-1 Desert Star Systems LLC, Monterey Bay, CA, USA via RS232 serial communication. The modem transmits the data to the other modem, which is placed underwater at 1 m depth with a maximum baud rate of 100 bit/sec with ultrasound communication. Finally, the data reaches a portable computer from RS232 serial interface of the acoustic modem. The data is displayed and logged on the computer based at the surface. The whole system is tested to 11 Bar in hyperbaric chamber. The acoustical data link is first established between two computers located at surface to test the reliability of the communication. The acoustical link experiments were successful for 20 minutes of simulated signals for the depth, interstitial glycaemia, breathing frequency and temperature information. The overall efficiency was 80.1%, with 474 bytes sent and 378 bytes received. The bandwidth of the acoustical link is very low max 4 reading/min but is adequate for glycaemia monitoring that can be as low as 1 reading every 5 minutes. Finally the system recorded the interstitial glucose of divers in 8 open water dives successfully and will be beneficial for studying diabetic divers. The system has a potential to be used to verify and optimize the existing protocols on diabetic divers. It offers as well an emergency system to monitor the non-diabetic divers during extreme exposures such as saturation diving.

This work describes the dynamics of an underwater pipeline subjected to an incident flow composed of a uniform flow and a sinusoidal component. The motion equations of the pipeline and the fluid flow around the pipeline are solved simultaneously with a numerical model that considers in-line oscillations (one degree of freedom) and a second numerical model that additionally includes cross flow (two degrees of freedom). The amplitude response and drag forces on the pipe are compared for both models considering parameters such as the difference between the excitation and natural frequencies of pipelines and the relative value between the sinusoidal and uniform components of the incident flow. Important differences in numerical predictions of both models are observed when the excitation frequency is greater than the natural frequency of the system and when the amplitude of the oscillatory component of the incident flow is greater than the amplitude of the uniform flow. [ABSTRACT FROM AUTHOR]

The demand for raw materials is growing and deep-sea mining is becoming increasingly important. It is of great interest to be able to analyze materials directly in the deep sea for mining or research applications. Laser induced breakdown spectroscopy (LIBS) is a laser-based, non-contact method for analyzing material in terms of its elemental composition. This paper presents the design of a LIBS system to be operated in a water depth of up to 6000 meters. A compact double pulse laser with adaptable pulse interval was developed to address different water depths. The complete LIBS setup was tested in a pressure chamber and shows emission lines from zinc up to a water pressure of 600 bar. To the best of our knowledge, this was the first LIBS measurement at 600 bar water pressure. [ABSTRACT FROM AUTHOR]

Submarine permafrost is perennially cryotic earth material that lies offshore. Most submarine permafrost is relict terrestrial permafrost beneath the Arctic shelf seas, was inundated after the last glaciation, and has been warming and thawing ever since. As a reservoir and confining layer for gas hydrates, it has the potential to release greenhouse gasses and impact coastal infrastructure, but its distribution and rate of thaw are poorly constrained by observational data. Lengthening summers, reduced sea ice extent and increased solar heating will increase water temperatures and thaw rates. Observations of gas release from the East Siberian shelf and high methane concentrations in the water column and air above it have been attributed to flowpaths created in thawing permafrost. In this context, it is important to understand the distribution and state of submarine permafrost and how they are changing. We assemble recent and historical drilling data on regional submarine permafrost degradation rates and review recent studies that use modelling, geophysical mapping and geomorphology to characterize submarine permafrost. Implications for submarine permafrost thawing are discussed within the context of methane cycling in the Arctic Ocean and global climate change. [ABSTRACT FROM AUTHOR]

A valve is a mechanical component in a piping system that is used to open and close the fluid passage, avoid return of the fluid, control the flow, or for safety purposes. An industrial valve contains different parts in general, such as pressure-controlling and pressure-containing parts. The valve stem is categorized as a pressure-containing part, and failure of this component leads to leakage of the fluid to the environment. Thus, failure of the valve stem leads to asset losses, oil or gas spillage into the environment, human injury or death, and in general health, safety, and environmental concerns. Therefore, this article addresses some of the main stem design features to minimize the risk of failure in stem. The main design features are the maximum allowable stem torque to enable the stem to handle the operator torque or force, stem diameter calculation, material selection, anti-blow out and anti-static design. Different materials for the stem, especially those with high mechanical strength, are proposed in this article. The anti-blow out design feature and solutions for stem and closure member connection, as well as stem and body connection, have been explained in detail. The anti-static design will provide electrical continuity among the stem, ball, and body to minimize the risk of fire inside the valve due to the accumulation of static electricity in the valve's soft materials, which has been explained. The valve stem sealing is not included in this article and requires separate research. [ABSTRACT FROM AUTHOR]

This article undertakes a comprehensive investigation of the damage incurred by the Schilling-manufactured Titan 4 seven-function manipulator during the period of 2017–2022. This particular manipulator stands as the most widely employed equipment on work class remotely operated vehicles (ROVs) globally. The article delves into a detailed discussion of ROVs in general, with a specific focus on those belonging to the work class category. Furthermore, the manipulator is dissected into its constituent elements, as delineated by the manufacturer, and each individual component is subjected to separate evaluation. The damages that were encountered are described in detail, along with the corresponding repair processes. To quantify the likelihood of future damage to the various manipulator elements over the subsequent five-year period, the obtained damage results are inputted into the Geogebra program. This enables the calculation of the probability of damage occurrence for each individual component. The research findings are ultimately summarized and juxtaposed with the real-life experiences of ROV operators, which are captured through a meticulously designed questionnaire. The questionnaire is carefully constructed to elicit valuable insights from the operators regarding the most common faults or defects observed in the Titan 4 manipulator. It is important to note that this manipulator-focused investigation is based on the author's first-hand experience as a ROV Supervisor in the offshore oil and gas industry. The combination of practical expertise and the empirical data gathered from the questionnaire responses ensures a comprehensive and well-rounded examination of the Titan 4 manipulator and its associated operational challenges. • Leaks or damage to seals is the most common cause of damage to the manipulator. • The jaws of the manipulator are the element most exposed to damage. • There is a correlation between operator errors and manipulator damage. • It is possible to identify potential preventive measures against future failures. [ABSTRACT FROM AUTHOR]

• Generalized architecture of Offshore Power System establishes a framework. • Offshore power generation, transmission, distribution and consumption subsystems. • Also offshore energy storage, intelligence and environment subsystems. • Nuances between specific systems, influences of the oceanic environment. • Technologies and research for economic, social and military activities in oceans. This review describes the offshore power system (OffPS), a research area of electricity that—despite being deeply investigated in scattered fragments—has not been comprehensively conceptualized as an integral system of interrelated components, equipment, functions and subsystems. Part of this lack of systemic approach is due to the fact that this system normally does not subsist by itself. It depends on structural elements for protection and support. OffPS gathers all the characteristics of a system and has several configurations, subsystems, and functions. In many cases, OffPS is subjected to extreme forces imposed by offshore weather conditions. For this reason, it is duly enclosed, protected and supported by several offshore-resistant mechanical machines such as ships, submarines, offshore platforms, floating ports and power plants. The prevalence of OffPS has been geographically expanding in recent years and it is spreading over vast portions of the oceans. On a larger extent, it is evolving towards an offshore power grid, a network that connects countries and even entire continents. It is also adjusting to multi-agent power access, in what is called multi-terminal OffPS. In order to encompass such a variety of topologies and applications, a generalized architecture of OffPS is proposed. It establishes a basic framework for this review on the latest research advances in offshore power generation, transmission, distribution, consumption, energy storage, offshore intelligence and environment. Nuances between specific offshore power systems, influences of the surrounding environment, interactions between OffPS subsystems and other research areas are then described within this framework. The aim of this review is to facilitate a better systemic understanding of the major challenges and importance of offshore power system research in contemporary society. [ABSTRACT FROM AUTHOR]

The WITT (Whatever Input to Torsion Transfer) energy harvesting device converts chaotic motion in six degrees of freedom to a single unidirectional output, which can be coupled to a generator to provide electrical power. The WITT energy device of this size order has an operational sweet spot of approximately 2 Hz, with up to 100 mm amplitude displacements, although it is tunable within the WITT device by varying the pendulum length and mass. To operate in this nature, subsea vortex-induced vibration (VIV) was chosen to drive the system. This is achieved by connecting the WITT energy transmission to cylindrical cross-section pipe sections, creating a modular system that can be varied for sites with different conditions or power requirements. Numerical predictions were performed for a wide range of design variations over a broad range of operating conditions using different VIV calculation techniques. This informed the likely dimensions for different sites and power requirements, so that an off-the-shelf solution could be quickly provided to a client, providing a sealed modular subsea energy solution. Tank testing was performed to compare to the numerical predictions and determine the effect of the WITT energy device on the system dynamics, demonstrating the concept is feasible. A range of possible applications are provided, from powering subsea monitoring equipment through to reduction of riser fatigue by reducing VIV. [ABSTRACT FROM AUTHOR]

This paper presents a compilation of data describing interfacial tension between oil and seawater (IFT (oil-water)) as a function of dispersant dosage. The data are from several earlier laboratory studies simulating subsea oil blowouts to evaluate subsea injection of dispersant (SSDI). Three dispersants were tested with four oil types to give a large variation in oil properties (paraffinic, light, waxy and asphaltenic). A general expression for IFT (oil-water) as a function of dispersant dosage is proposed based on the compiled data. IFT (oil-water) versus dosage is needed by algorithms to predict oil droplet sizes from subsea releases. However, such a relationship based on averaged data should be used with care and IFT measurements on the actual oil-dispersant combination should always be preferred. • Subsea release of oil and gas is simulated in a 6 m high tower basin. • IFT (oil-water) is measured on oil sampled in-situ during tank experiments. • Data is compiled from experiments with multiple dispersant and oil types. • An equation is suggested for IFT (oil-water) as a function of dispersant dosage. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid-boost Modular Multilevel Converter (MMC) for the Medium-Voltage (MV) Variable Speed Drives (VSDs) employed in subsea applications, such as oil and gas recovery. In the presented architecture, a hybrid-boost MMC with a reduced number of semiconductor devices driving a multiphase Induction Machine (IM) is investigated. The stepped output voltage generated by the MMC reduces or eliminates the filtering requirements. Moreover, the boosting capability of the proposed architecture eliminates the need for bulky low-frequency transformers at the converter output terminals. A detailed illustration of the hybrid-boost MMC operation, the expected limitations/constraints, and the voltage balancing technique are presented. A simulation model of the proposed MV hybrid-boost MMC-based five-phase IM drive has been built to investigate the system performance. Finally, a downscaled prototype has been constructed for experimental verification. [ABSTRACT FROM AUTHOR]

Abstract Both oil droplets and gas bubbles have simultaneously been quantified in laboratory experiments that simulate deep-water subsea releases of both live oil (saturated with gas) and additional natural gas under high pressure. These data have been used to calculate particle size distributions (50–5000 μm) for both oil and gas. The experiments showed no significant difference in oil droplet sizes versus pressure (from 5 m to 1750 m) for experiments with live oil. For combined releases of live oil and natural gas, oil droplet sizes showed a clear reduction as a function of increased gas void fraction (increased release velocity) and a weak reduction with increased depth (increased gas density/momentum). Oil droplets were reduced by a factor of 3 to 4 during simulated subsea dispersant injection (SSDI) and no significant effect of pressure was observed. This indicates that SSDI effectiveness is not dependent on water depth or pressure. Highlights • Subsea release of oil and gas under high pressure is simulated in the laboratory. • Particle distributions of gas bubbles and oil droplets are quantified simultaneously. • The experiments were performed with oil saturated by natural gas (live oil). • Oil droplet formation was not found to be dependent of depth or pressure. • Reduction in droplet size during dispersant injection showed no pressure dependency. [ABSTRACT FROM AUTHOR]

Abstract There is an upcoming "P&A wave" of wells that need to be permanently plugged and abandoned, especially in mature, offshore areas such as the North Sea and Gulf of Mexico. It is important to ensure that plugged wells do not leak after abandonment, as there could be several potential leak paths such as microannuli in plugged wells. To ensure well integrity after abandonment, permanent well barriers must extend across the full cross section of the well. That includes establishing barriers in all annuli, which could however be quite time-consuming and thus costly. This paper is a review of challenges and technologies for P&A of offshore wells, with an emphasis on cost-effective solutions while establishing permanent well barriers. An overview of cement and other plugging materials is given, as well as a discussion of different types of potential leak paths and failure mechanisms in permanently plugged and abandoned wells. Moreover, recent technology developments such as utilizing shale as barrier for P&A are described. A discussion on the special considerations related to P&A of subsea wells is also included. [ABSTRACT FROM AUTHOR]

Abstract Limited experimental and field data are available describing oil droplet formation from subsea releases at high pressure. There are also analytical challenges quantifying oil droplets over a wide size and concentrations range at high pressure. This study quantified oil droplets released from an orifice in seawater at low and high pressure (5 m and 1750 m depth). Oil droplet sizes were quantified using a newly developed sensor (Silhouette camera or SilCam). The droplet sizes measured during experiments at low and high pressure, using the same release conditions, showed no significant difference as a function of pressure. This lack of a pressure effect on oil droplet sizes was observed for both untreated oil and for droplet formation during subsea dispersant injection or SSDI. This strongly indicates that the effectiveness of SSDI is not influenced by water depth or pressure, at least for simulated subsea releases of oil alone (no gas). Highlights • Limited data exists on oil droplet formation from subsea releases at high pressure. • Experiments were performed at pressure corresponding to 5 and 1750 m depth. • No significant difference in oil droplets sizes was observed at high & low pressure. • This was also observed during dispersant injection (1 & 2% dosage). • This indicates that dispersant injection effectiveness is not dependant on pressure. [ABSTRACT FROM AUTHOR]

The article presents the effectiveness of a subsea optical wireless communication (OWC) system comprising a light-emitting diode (LED) transmitter and a photodiode (PD) receiver when operated at various water depths in the Arabian Sea. An optical attenuation profile identified from solar hyperspectral irradiance measured in up to a 90-m water depth in the Arabian Sea using a remotely operated vehicle is used as inputs to the subsea OWC communication effectiveness assessment (CEA) model developed using MATLAB. It is identified that a 30-W LED-PD-based OWC system, with the noise equivalent power of 10−12 W/√Hz, could have a horizontal range and data rate of 146 m and 1 Mbps in water depths ≥220 m in the Arabian Sea. For the same data rate, the horizontal range reduces to 65 m at a 90-m water depth in the same location during the day. In coastal waters, the system could have a data rate of 10 kbps at a 30-m range. A six-fold increase in the transmitter electrical power could increase the horizontal range by a factor of 1.5. An experimental 30-W LED-PD-based OWC system developed and operated in a calibrated tank facility is found to have a data rate and range of 3.2 Mbps and 3 m, respectively. The performance of the prototype complies with the ideal CEA model with an accuracy of 84% under similar inherent channel property and apparent system parameters. Keywords: optical, subsea, wireless communication [ABSTRACT FROM AUTHOR]

The main objective with subsea mechanical dispersion (SSMD) is to influence the fate of an oil spill in the marine environment by significantly reducing oil droplet sizes from subsea release of oil. Earlier studies have indicated that the capability of SSMD to reduce oil droplet sizes is comparable to subsea dispersant injection (SSDI). Earlier testing of SSMD has mainly used a low viscus paraffinic oil. Focus for this study was to study SSMD and SSDI effectiveness using five oil types spanning out a wide variation of relevant oil properties. Effectiveness was quantified as the reduction in oil droplet sizes measured by a Silhouette camera. Testing of the two technologies were completed in the same experiment on a simulated subsea release. The results show a variation in effectiveness for both technologies as a function of oil properties. SSMD and SSDI showed comparable effectiveness for all oils tested. • A new technology for dispersion of oil from a subsea blow-out is presented - subsea mechanical dispersion (SSMD). • Laboratory testing shows high dispersion effectiveness using a high velocity water jet for SSMD. • Testing of subsea dispersant injection (SSDI) was also performed with the same five oil types. • SSMD and SSDI effectiveness showed no significant differences as a function of oil properties. • High SSMD effectiveness is obtained with experimental conditions relevant for operational use subsea. [ABSTRACT FROM AUTHOR]