Showing papers on "Submarine pipeline published in 2022"

Geological evolution of offshore pollution and its long-term potential impacts on marine ecosystems

Abstract: • Increasing global offshore pollution as a worldwide problem. • Coastal geological disasters due to global offshore pollution. • Complex offshore sedimentary dynamics through long-term accumulating pollutants. • The stable succession and development trend of marine ecosystems was significantly interrupted. Populations and metropolitan centers are accumulated in coastal areas around the world. In view of the fact that they are geographically adjacent to coasts and intense anthropogenic activities, increasing global offshore pollution has been an important worldwide concern over the past several decades and has become a very serious problem that needs to be addressed urgently. Due to offshore pollution, various geological disasters occur in high frequency, including intensified erosion and salinization of coastal soils, frequent geological collapses and landslides and increasing seismic activities. Moreover, offshore pollution shows increasingly serious impacts on the topography and geomorphology of offshore and coastal areas, including coastal degradation, retreating coastlines and estuary delta erosion. Offshore sedimentation processes are strongly influenced by the pH changes of terrestrial discharges, and sedimentary dynamics have become extremely acute and complex due to offshore pollution. The seabed topography and hydrodynamic environment determine the fate and transport of pollutants entering offshore regions. Coastal estuaries, port basins and lagoons that have relatively moderate ocean currents and winds are more likely to accumulate pollutants. Offshore regions and undersea canyons can be used as conduits for transporting pollutants from the continent to the seabed. It is particularly noteworthy that the spatial/temporal distribution of species, community structures, and ecological functions in offshore areas have undergone unprecedented changes in recent decades. Due to increasing offshore pollution, the stable succession and development trend of marine ecosystems has been broken. It is thus important to identify and regulate the quantity, composition and transportation of pollutants in offshore regions and their behavior in marine ecosystems. In particular, crucial actions for stabilizing marine ecosystems, including increasing species and biodiversity, should be implemented to enhance their anti-interference capabilities. This review provides an overview of the current situation of offshore pollution, as well as major trends of pollutant fate and transportation from continent to marine ecosystems, transformation of pollutants in sediments, and their bioaccumulation and diffusion. This study retrospectively reviews the long-term geological evolution of offshore pollution from the perspective of marine geology, and analyses their long-term potential impacts on marine ecosystems. Due to ecological risks associated with pollutants released from offshore sediments, more research on the influence of global offshore pollution based on marine geology is undoubtedly needed.

Mapping of the levelised cost of energy for floating offshore wind in the European Atlantic

Abstract: Understanding the spatial variation of the levelised cost of energy (LCOE) of offshore wind is fundamental for identifying potential areas for the development of this technology. With this in view, this paper presents a large-scale mapping of the LCOE of floating offshore wind over the European Atlantic, with a focus on floating semi-submersible platforms. The energy production is estimated accurately at every site using hindcast wind data combined with the power curve of an exemplar wind turbine. Furthermore, this work presents an analysis of the different costs incurred in the lifetime of the project using expressions depending on site-specific variables, i.e., water depth and distance to shore. The results highlight the paramount influence of the energy production and, therefore, the wind resource on the final cost of energy. The lowest LCOE values (∼95 €/MWh) correspond to the areas where the wind resource is most abundant: off Great Britain and Ireland, in the North Sea and off NW Spain. The influence of the resource leads inevitably to LCOE values somewhat higher off Portugal and Norway (∼125 €/MWh), and much higher in the Gulf of Biscay and south of the Iberian Peninsula (>160 €/MWh). Within regions with a similar resource, e.g., the North Sea (LCOE in the range 95–135 €/MWh), the distance to shore is found to be the main variable affecting the LCOE. By comparison, the costs related to water depth (primarily, mooring costs) are of little significance – unlike with bottom-fixed technologies.

Mapping of the levelised cost of energy for floating offshore wind in the European Atlantic

Abstract: Understanding the spatial variation of the levelised cost of energy (LCOE) of offshore wind is fundamental for identifying potential areas for the development of this technology. With this in view, this paper presents a large-scale mapping of the LCOE of floating offshore wind over the European Atlantic, with a focus on floating semi-submersible platforms. The energy production is estimated accurately at every site using hindcast wind data combined with the power curve of an exemplar wind turbine. Furthermore, this work presents an analysis of the different costs incurred in the lifetime of the project using expressions depending on site-specific variables, i.e., water depth and distance to shore. The results highlight the paramount influence of the energy production and, therefore, the wind resource on the final cost of energy. The lowest LCOE values (∼95 €/MWh) correspond to the areas where the wind resource is most abundant: off Great Britain and Ireland, in the North Sea and off NW Spain. The influence of the resource leads inevitably to LCOE values somewhat higher off Portugal and Norway (∼125 €/MWh), and much higher in the Gulf of Biscay and south of the Iberian Peninsula (>160 €/MWh). Within regions with a similar resource, e.g., the North Sea (LCOE in the range 95–135 €/MWh), the distance to shore is found to be the main variable affecting the LCOE. By comparison, the costs related to water depth (primarily, mooring costs) are of little significance – unlike with bottom-fixed technologies.

Review of Past Gas Production Attempts from Subsurface Gas Hydrate Deposits and Necessity of Long-Term Production Testing

Abstract: This paper summarizes the conditions, applied techniques, results, and lessons of major field gas production attempts from gas hydrates in the past and the necessity of longer term production testing with the scale of years to fulfill the gap between the currently available information and the knowledge required for commercial development. The temporal and spatial scales of field production test projects employing depressurization have expanded since 2002. The results from the projects have proved the applicability of these techniques in both onshore and offshore conditions. However, many technical and reservoir condition-related issues have emerged in gas production, and the gap between current status and industrial requirements is still large. Sand control, artificial lift, and related flow assurance issues are common technical issues that impact onshore and offshore production testing operations. Different reservoir responses were observed well by well, and discrepancy between model predictions and actual field measurements were seen, although reasonable matches were made for short-term behaviors. Those observations suggest that temporal change of the wellbore and near-wellbore conditions and reservoir heterogeneity that cannot be fully modeled have caused complex short-term responses to the depressurization operations. To ensure the long-term operational stability and reliability of the prediction technologies for production behaviors that are essential for commercialization of gas hydrate resources, gas hydrate production testing with comparable duration with commercial operations are necessary. Due to the locality of geological conditions in gas hydrate reservoirs, numerous gas production tests will be required to understand the factors controlling gas production.

Understanding the fluid–structure interaction from wave diffraction forces on CALM buoys: numerical and analytical solutions

Abstract: ABSTRACT This research fills the gap in understanding fluid–structure interaction (FSI) from wave diffraction forces on CALM buoys and cylindrical structures, based on the hydrodynamics with connections. Recently, there is an increased application of (un)loading marine hoses for Catenary Anchor Leg Moorings (CALM) buoy systems in the offshore industry due to the need for more flexible marine structures that are cost-saving, easier to install, and service. However, different operational issues challenge these hoses, like during hose disconnection. Also, the fluid behaviour was investigated based on the analytical and numerical models. The numerical modelling involves the boundary element method (BEM) and Orcaflex line theory. Hydrodynamic analysis is conducted on the disconnection-induced load response of marine bonded hoses during normal operation and accidental operation under irregular waves. A comparative study on hose performance during normal operation and accidental operation is also presented. Results of statistical analysis on CALM buoy system shows good motion characteristics.

Review of Composite Marine Risers for Deep-Water Applications: Design, Development and Mechanics

Abstract: In recent times, the utilisation of marine composites in tubular structures has grown in popularity. These applications include composite risers and related SURF (subsea umbilicals, risers and flowlines) units. The composite industry has evolved in the development of advanced composites, such as thermoplastic composite pipes (TCP) and hybrid composite structures. However, there are gaps in the understanding of its performance in composite risers, hence the need for this review on the design, hydrodynamics and mechanics of composite risers. The review covers both the structure of the composite production riser (CPR) and its end-fittings for offshore marine applications. It also reviews the mechanical behaviour of composite risers, their microstructure and strength/stress profiles. In principle, designers now have a greater grasp of composite materials. It was concluded that composites differ from standard materials such as steel. Basically, composites have weight savings and a comparative stiffness-to-strength ratio, which are advantageous in marine composites. Also, the offshore sector has grown in response to newer innovations in composite structures such as composite risers, thereby providing new cost-effective techniques. This comprehensive review shows the necessity of optimising existing designs of composite risers. Conclusions drawn portray issues facing composite riser research. Recommendations were made to encourage composite riser developments, including elaboration of necessary standards and specifications.

Experimental Study on Motion Characterisation of CALM Buoy Hose System under Water Waves

Abstract: The application of marine bonded hoses has increased in recent times, due to the need for more flexible conduits and flexible applications in the offshore industry. These marine structures include Catenary Anchor Leg Moorings (CALM) buoys and ocean monitoring buoys. Their attachments include floating hoses, submarine hoses and submarine cables. However, the structural performance challenges of a CALM buoy system from its hydrodynamics water waves and other global loadings, have led to the need for this investigation. In this study, a detailed presentation on the motion characterisation of the CALM buoy hose system is presented. The CALM buoy is a structure with six degrees of freedom (6DoF). A well-detailed experimental presentation on the CALM buoy hose model conducted in Lancaster University Wave Tank is presented using three novel techniques, which are: a digital image captured using Imetrum systems, using an Akaso 4K underwater camera, using wave gauges arranged in a unique pattern and using underwater Bluetooth sensors. The buoy model was also found to respond uniquely for each motion investigated under water waves. The results showed that the higher the profile, the higher the response of the buoy. Thus, this study confirms the existence of flow patterns of the CALM buoy while floating on the water body.

Offshore Island Connection Line: A new perspective of coastal urban development boundary simulation and multi-scenario prediction

Abstract: ABSTRACT The urban development boundary (UDB) is a core issue in territorial spatial planning and remains a research focus in urban development. However, in the past, land use simulations of coastal cities have had some limitations. For example, new urban land outside the research boundary could not be effectively simulated, resulting in a large gap between the simulation results and reality. In this study, an artificial neural network (ANN) cellular automata (CA) model based on a new perspective, the Offshore Island Connection Line (collectively, OICL-ANN-CA), was developed to address this problem. We first proposed the delineation principles and methods of OICL and applied it to the Jinpu New Area of Dalian City, Liaoning Province, China. Based on the conversion probability and land use simulation results obtained by ANN and CA, this study validated the UDB simulations for 2000–2020 in the Jinpu New Area and predicted the UDB for 2020–2035 under three scenarios: historical inertia development, ecological security protection, and ecological and economic balance. The results indicate that, compared with the traditional perspective model (the ANN-CA model based on the sea–land boundary), the OICL-ANN-CA model exhibited better simulation accuracy (the figure of merit was approximately 35% higher) and effectively simulated new urban land outside the traditional boundary. This simulation of urban land expansion is more consistent with recent development in the study area. In addition, the predicted results of UDB in 2035 also demonstrate the benefits of this model for detecting reclaimed land. This study illustrates that the OICL-ANN-CA model is a more capable method for capturing changes in new coastal urban land and can produce realistic simulations. It provides a reference for delimiting the UDB and defining the research boundary for the Jinpu New Area and other fast-growing coastal cities in China.

Local scour at offshore windfarm monopile foundations: A review

Abstract: In this article, current research findings of local scour at offshore windfarm monopile foundations are presented. The scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are summarized, including the current-only condition, wave-only condition, combined wave-current condition, and complex dynamic condition. Furthermore, this article analyzes the influencing factors on the basis of classical equations for predicting the equilibrium scour depth under specific conditions. The weakness of existing researches and future prospects are also discussed. It is suggested that future research shall focus on physical experiments under unsteady tidal currents or other complex loadings. The computational fluid dynamics-discrete element method and artificial intelligence technique are suggested being adopted to study the scour at offshore windfarm foundations.

Main Control Factors and Prediction Model of Flow-accelerated CO2/H2S Synergistic Corrosion for X65 Steel

Abstract: As an important infrastructure for offshore petroleum development, submarine pipelines are the lifeline of offshore petroleum resources development. However, the medium flow containing H2S and CO2 threatens the normal production of oil fields. Based on 18 groups of orthogonal experiments, considering CO2 partial pressure, H2S partial pressure, temperature, pH, chloride concentration and liquid flow rate, the general and local corrosion rate were obtained. The corrosion products were characterized with SEM/EDS and XRD. The main controlling factors and corrosion mechanism were explored. Under the experimental conditions, CO2 and H2S were the main controlling factors of general and local corrosion. With the increase of gas partial pressure, the corrosion rate increaseed gradually. Flow accelerated the synergistic corrosion mechanism and model were established. Within the working condition range, the prediction error was less than 20%, which was better than ECE prediction model. The results can improve the integrity management of submarine pipelines.

Prediction of Significant Wave Height in Offshore China Based on the Machine Learning Method

Abstract: Accurate wave prediction can help avoid disasters. In this study, the significant wave height (SWH) prediction performances of the recurrent neural network (RNN), long short-term memory network (LSTM), and gated recurrent unit network (GRU) were compared. The 10 m u-component of wind (U10), 10 m v-component of wind (V10), and SWH of the previous 24 h were used as input parameters to predict the SWHs of the future 1, 3, 6, 12, and 24 h. The SWH prediction model was established at three different sites located in the Bohai Sea, the East China Sea, and the South China Sea, separately. The experimental results show that the performance of LSTM and GRU networks based on the gating mechanism was better than that of traditional RNNs, and the performances of the LSTM and GRU networks were comparable. The EMD method was found to be useful in the improvement of the LSTM network to forecast the significant wave heights of 12 and 24 h.

In‐situ observation of storm‐induced wave‐supported fluid mud occurrence in the subaqueous Yellow River delta

Abstract: Two relatively comprehensive and long-term observation campaigns of bottom sediment dynamics have been conducted at the subaqueous Yellow River delta in the winters of 2016 and 2018. High suspended sediment concentration (SSC) up to 10 g/L were observed in 2016 and active events of wave-supported fluid mud (WSFM) were found to exist at the abandoned river delta during storms in 2018. A set of calibrated optical backscatter sensors measured the near-bed SSC >30 g/L with a maximum WSFM thickness >60 cm. WSFMs emerging at the abandoned river delta were classified into three types: single-peak, multi-peak, and hybrid according to the time-varying characteristics of WSFMs. The dominant factors triggering the WSFM generation and dissipation are storm-wave actions and tidal effects, with limited contribution from current-induced turbulence. In this study, several lines of evidence were put forward to prove the presence of seabed liquefaction to a depth of 10–16 cm, and thus we can infer that another significant factor enhancing the WSFM thickness scale may be wave-induced liquefaction. Observations showed obvious signs of WSFM motion, or in other words, wave-supported gravity flow (WSGF) moved downslope. The downslope velocity (around 1.9 cm/s) was estimated by solving a buoyancy-friction force balance. This study observed frequent WSFM events at the abandoned Yellow River delta for the first time and demonstrates the need to attach more concerns about its roles in sediment transport and offshore engineering in the future.

Finite Element Modelling on the Mechanical Behaviour of Marine Bonded Composite Hose (MBCH) under Burst and Collapse

Abstract: Currently, the properties of composites have been harnessed on pipelines in the marine offshore industry. In this study, marine bonded composite hose (MBCH) is presented. It is aimed at understanding the stress/strain distribution on marine bonded hoses using local design pressure under burst and collapse cases. This study also investigates composite material modelling, hose modelling, liner wrinkling, helical spring deformation, and two MBCH models—with and without ovalisation. The ovalized model is considered the simplified model in this research. A mesh study was carried out on meshing the hose layers. In this study, local design pressure was considered and not operational pressure. This finite element model was adopted to predict the deformation and mechanical response behaviour of MBCH. From this study, composites could be considered to improve conventional marine hoses. The study findings include identification of buckled sections on the hose and stressed zones on the helix reinforcement. Highly reinforced hose ends are recommended in ends of the MBCH as they had maximum stress and strain values.