bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Study on the Influence of Hydraulic Fracturing on Hydrogen Sulfide Generation in Longxi Block of Daqing Oilfield
Authors: Sun Hongyu , Zhong Liguo , Liu Jianbin , Hao Tongchun , Li Shihao , Zhu Yu , Zhang Hailong , Wang Kexin 
Published: October 2022

Abstract
Hydraulic fracturing has a significant effect on increasing production and injection of oil and water wells in low-permeability and tight reservoirs. Hydrogen sulfide (H2S) was generated after hydraulic fracturing of oil and water wells in Longxi Block of Daqing Oilfield. The maximum hydrogen sulfide content in casing gas reached 232 ppm, far exceeding the safety critical concentration value (20 ppm), which increased the risk and difficulty of production and construction operation. In order to reveal the influence mechanism of fracturing on H2S generation in Daqing oilfield, the experimental simulations of the thermal decomposition of sulfur (TDS), thermochemical sulfate reduction (TSR) and bioreduction reaction of sulfate-reducing bacteria (SRB) with different compositions of fracturing fluid at different temperatures were conducted in this paper. The results showed that the influence mechanism of the fracturing fluid compositions on the formation of H2S was different when the formation temperature was different. The critical temperature of TDS and TSR reaction in the formation was 100°C and 140°C, respectively. The higher the temperature, the higher the amount of H2S was generated. The potassium persulfate (K2S2O8) and sodium sulfite (Na2SO3) in the fracturing fluid could promote the TDS and TSR reaction to generate H2S, but did not change the critical reaction temperature of TDS and TSR reaction. When the formation temperature was not higher than 56°C, the guar gum and sulfur-containing materials in the fracturing fluid could provide nutrition for SRB in the formation, which promoted the rapid reproduction of SRB in a short period of time, and then generated a large amount of H2S. The mechanism of H2S generation for fractured wells in the Longxi block with temperature of 30∼56°C was the proliferation of SRB in the fracturing fluid. The mechanism of H2S generation in fractured wells with temperature of 100∼120°C was that sulfur-containing materials promoted TSR reaction. This study clarifies the reasons and conditions for the generation of H2S, and plays an important role in the subsequent research on H2S prevention and control measures.
Numerical Modelling of Residual Liquefaction in the Subsoil Under a Vibrating Plate
Authors: Shanmugasundaram Ranjith Khumar , Rusche Henrik , Windt Christian , Kirca V. S. Özgür , Sumer B. Mutlu , Goseberg Nils 
Published: October 2022

Abstract
Seabed liquefaction is the phenomenon by which the seabed soil loses its strength and stiffness, due to applied stress, and behaves like a non-Newtonian fluid. Seabed liquefaction can lead to severe failure of marine structures, such as buried pipelines or coastal breakwaters. Numerical modelling of liquefaction can provide valuable insights into the prevailing wave-structure-soil interaction. However, the holistic modelling of seabed liquefaction, including the transition from solid to liquid and back to solid soil, is challenging, due to the prevailing hydrogeotechnical processes. As a step towards the development of such a holistic numerical model of seabed liquefaction, this paper considers the modelling of the soil under a rocking plate as an idealised representation of a caisson breakwater as presented in [1]. The numerical model has recently been presented in [2] and includes equations for the accumulation of pore pressure and a criterion to distinguish between the liquefied and non-liquefied regions. The numerical results are compared to the experimental results taken from [1]. Different numerical model setups are presented to overcome modelling challenges due to occurring punching shear failure.
Cost-Effective Optimal Solutions for Steel Catenary Riser Using Artificial Neural Network
Authors: Abam Joshua T. , Pu Yongchang , Hu Zhiqiang 
Published: October 2022

Abstract
Over decades, free-hanging steel catenary riser (SCR) has been regarded as a cost-effective and straightforward system for riser solutions in deepwater and ultra-deepwater by National oil companies NOCs, international oil companies IOCs, and independent players. However, the free-hanging SCR comes with its own challenges, which, if not correctly evaluated during design stages, can result in system failures. The two main challenges facing the free-hanging SCR usage are increased self-weight and high fatigue damage, especially at the touchdown and hang-off points. Fatigue damage is the failure resulting from cyclic stress accumulation over a specific duration. The involvement of technologies has improved the design method for these systems over the years. Two of such innovative contributions include the optimisation algorithm and artificial neural network ANN methods. The aim of this research is to develop an effective optimisation algorithm to search for the global optimal weight of the riser configuration while maintaining its structural integrity. The method involves the combined use of ANN and optimisation genetic algorithms (GA) to determine the optimum solution of the SCR. The GA is used because of its capability in handling a variety of complex nonlinear optimisation problems to ascertain the global optimum solution and its capacity to self-moderate the number of iterations. At the same time, the ANN method is deployed for its accurate prediction of non-linear responses. The deployed techniques have shown to be promising due to the time-saving and less computational cost compared to integrating GA and time-domain FE models. This method was illustrated using a prospective 10-inch internal diameter SCR installed in a 2000m deepwater offshore field off the oil-rich Niger Delta region, Nigeria. The obtained results have shown a 19.10 per cent reduction in the riser weight and a time reduction of 90.83 per cent.
Influence of Extreme Environmental and Deep-Sea Temperature Conditions on Silicone Oil Used for Insulating Underwater Electrical Switching Systems
Authors: Haba Yvonne , Arumugam Saravanakumar , Krohmann Sascha , Körner Gerhard , Richert Ranko , Kosleck Sascha 
Published: October 2022

Abstract
This study focuses on understanding the influence of extreme environmental conditions on silicone oil applied as an insulating material in underwater electrical switching systems. The extreme environmental conditions imply adverse operating temperatures of the underwater electrical systems which must be effectively handled by the silicone oil. For this purpose, a standard high voltage (HV) relay is selected and is immersed in a silicone oil thereby enhancing its operating voltage to 20 kV. First, the geometry of the modified relay switch is captured and converted into a CAD model. Subsequently, the developed CAD model is imported into the simulation software and converted into a numerical model and subjected to AC/DC, electrostatic and stationary case simulation. The adverse temperature conditions are varied i.e., from −50 °C, 0 °C, 20 °C, 40 °C and 120 °C respectively. The potential and electric field displacement at the electrodes of the high voltage relay is recorded and analyzed. Following this, high voltage experiments are carried out on an actual high voltage relay constructed based on the simulation model and the respective parameters such as discharges. Thus, the dielectric quality of the silicone oil under wide range of temperature is studied. The simulation and experimental results obtained altogether validate the design modifications made on the standard relay converted to meet the high voltage requirements of underwater electrical switching systems.
Once this is identified, the chosen relay is compared with the experimental findings to validate the design modification.
Numerical Investigation of Mean Drift Forces Acting on Restrained FPSO in Regular Waves by Linear and Nonlinear Tools
Authors: Pakozdi Csaba , Fonseca Nuno 
Published: October 2022

Abstract
State of the art ULS/ALS mooring analysis is based on potential flow calculated wave drift forces. However, it is acknowledged that higher order effects in steep sea states increase the wave drift forces as compared to the potential flow 2nd order models. This is the background for the EXWAVE 2 JIP where semi-empirical methods to correct wave drift forces were implemented and checked, which shows the significance of this problem to the industry.
This publication aims at applying CFD simulations to better understand the physics of wave drift loads in steep sea states and to identify higher than 2nd order effects.
Calculations are performed with a RANSE-VOF based CFD code and with a linear potential flow code for a floating production storage and offloading (FPSO) unit in deep water regular waves with three periods and three wave steepnesses. The vessel is restrained from moving to make a simple and a consistent comparison between the results from the two approaches. Comparisons for small amplitude waves provide an assessment of the quality of the CFD simulations, while increasing wave steepness conditions are used to identify higher than second order effects on the wave drift forces.
CFD simulation resulting force time series are decomposed into mean value and harmonics by means of a Fourier analysis and compared against potential theory estimated mean and first order forces.
The comparisons for small wave amplitudes show a good agreement, which proofs the correctness of the applied CFD setup. Further, the CFD results show an increasing trend of the mean wave forces normalized by the wave amplitude squared with increasing wave steepness for the two shorter wave periods. The trend is unclear for the longer wave period.
Adhesively Bonded FRP Reinforcement of Steel Structures: Surface Preparation Analysis and Influence of the Primer
Authors: Sourisseau Quentin , Leprêtre Emilie , Chataigner Sylvain , Chapeleau Xavier , Mouton Luc , Paboeuf Stéphane 
Published: October 2022

Abstract
In tropical areas, with marine environment, high temperature and humidity, corrosion is a constant threat. The maintenance of steel structures (like FPSO’s) is becoming a challenge. The current technique of “crop and renewing” repair involves a certain number of major issues for project owners such as: “hot work”, that is to say welding; temporary weakening of the structure; need to empty, clean and purging the oil tanks of the FPSO’s, resulting in long downtime and an expensive solution. “Cold repair”, such as composite repair, is a promising solution. However, surface preparation and the influence of the primer are crucial issues to be addressed to ensure the strength and reliability of this type solution based on bonded patch.
The paper presents an experimental study of the influence of the surface preparation and the primer on the strength of small steel bonded specimens which have been deliberately degraded by corrosion and pollution. Several surface preparation methodologies were investigated and the quality of these preparations was assessed using methods that can be implemented on site. Two main aspects were investigated: the detection of the residual presence of pollutants through the use of a portable infrared spectrometer; and the determination of surface energy after preparation using contact angle and wettability measurement equipment. To study the impact of the primer on the adhesion capacity of the steel surface, critical toughnesses measurements was performed with End notch flexure tests. Three configurations have been tested: bonding with the epoxy resin without initial application of primer and bonding with the Epoxy resin with initial application of two Primer A and B. The results shown clearly that the type of primer and the quality of its application are paramount importance to ensure the strength of steel bonded patches.
Weight Optimisation of Steel Catenary Riser Using Genetic Algorithm and Finite Element Analysis
Authors: Abam Joshua T. , Pu Yongchang , Hu Zhiqiang 
Published: October 2022

Abstract
Steel catenary risers (SCR) are a good candidate for deepwater exploration due to their relatively low cost, less demand for subsea intervention, and compliance with the floating structures motions. However, SCR deployment in deepwater faces tremendous challenges such as increased top tension and concern over fatigue performance. This paper aims to search for the global optimal solution of a riser system through the application of genetic algorithm (GA) and finite element analysis. The process method will, in turn, automate the design process, with the implementation of an optimisation routing as a critical resource for initiating and finalising the acceptability of a riser system. The method involves the deployment of GA as the optimiser because of its capability in handling a variety of complex non-linear optimisation problems to ascertain the global optimum solution and the capacity to self-moderate the number of iterations. The total structural weight is the objective function, while bursting criteria, buckling (collapse) criteria, buckling propagation criteria, yielding criteria, and fatigue limit state (FLS) criteria are non-linear constraints. To accurately assess the strength requirements, time-domain approach through OrcaFlex is used to predict the dynamic responses and fatigue life/damage of the SCR. An interface between GA in MATLAB and ORCAFLEX has been programmed to exchange data. The wall thickness, length and declination angle at the hanging-off point are chosen as design variables due to their strong influence on the configuration and dynamic responses of a SCR.
This method was illustrated using a prospective 10inch SCR installed in a 2000m deepwater offshore field off the coast of the oil-rich Niger Delta region, Nigeria. The obtained results have shown a significant reduction in the riser weight.
Effects of Nonlinearity on the Formulation of the Crest Elevation and the Crest Width of Extreme Waves in Random Seas
Authors: Spiliotopoulos George , Katsardi Vanessa 
Published: October 2022

Abstract
This work highlights the effects of nonlinearity on extreme events that rise during directional focused and random wave simulations in finite water depths. For this purpose, the fully nonlinear model “HOS-Ocean” by Ducrozet et al. (2016) [1] is considered and compared with linear simulations. Large waves are formed through a series of linear and nonlinear focused and random simulations. The effect of water depth and directionality is considered by applying different directional spreadings relative to a range of short crested to long crested sea states. The results offer transparency in understanding the physics underlying such extreme events. It is shown that “walls of water” are also formulated infinite water depth, as is the case for deep water [2]. Indeed, the sea-state becomes more long-crested during the formulation of the extreme events in both focused and random simulations; all highly dependant on the directionality of the wavefield. The above is highlighted in the substantially increased crest width measured in the nonlinear simulations despite the decreased maximum crest elevations.
A Monte Carlo Approach for Fatigue Analysis of Mooring Lines Subjected to Simultaneous Environmental Actions
Authors: Seabra Pedro de Amorim , de Oliveira Mauro Costa , Simão Marina Leivas , Videiro Paulo Mauricio , Sagrilo Luis Volnei Sudati 
Published: October 2022

Abstract
Fatigue damage assessment of mooring lines components is one of the main issues in the design and life extension monitoring of deepwater floating production units mooring systems. Floating units operating at several ocean regions, as in the Brazilian southeast coast and Africa west coast, are almost permanently subjected to wind-sea waves and remote waves (swell), besides wind and marine current actions. Fatigue assessment of mooring systems operating under these environmental conditions shall consider an extensive number of simultaneous environmental action load cases or rely on some simplification of the load cases. In the first case, the fatigue assessment may require a large amount of computer resources and time, making it unfeasible, for example, in the early phases of the mooring system design, where normally the analysis of several configurations is necessary. In the second case, some important aspects of the actual behavior of the environmental actions may not be considered in the fatigue analyses.
This paper presents a new engineering approach for the fatigue assessment of mooring systems based on a Monte Carlo Simulation resampling using a set of simultaneous environmental conditions available in a database, sampled every 3 hours during several years. Studies show that damage estimates considering just a few resampled cases, say 5 to 10% of the cases in the database, compare very well to estimates considering the entire database. Finally, the paper also presents how to define confidence intervals of the damage estimates.
Influence of Grease Lubrication on Fretting-Fatigue Damages of Steel Wire Ropes
Authors: Montalvo S. , Fouvry S. , Martinez M. 
Published: October 2022

Abstract
Steel wire ropes can be used as mooring lines for Floating Offshore Wind Turbines. Swell induces tension and bending in the line. Investigating the effects of combined loads on rope lifetime is necessary. In these cases, fretting-fatigue damage is considered to be one of the main causes of failure. To prevent corrosion, grease is injected in the rope. The effect of grease on the fretting-fatigue damage of two wires in contact was investigated. A multi-scale approach was applied to calculate representative local loads in the mooring ropes. Global tension and bending were applied to a detailed model of the rope to calculate the local stress and contact forces in the steel wires. These are the fretting-fatigue loads applied in the laboratory tests. Two series of fretting-fatigue tests were conducted, each one with clean and greased wires. A two actuators hydraulic rig was used, allowing for complete decoupling of the fretting and fatigue loads. In the first series, the fatigue load was kept constant, and the fretting load was changed. In partial slip regime, for small fretting amplitudes, greased wires have longer lifetimes than non-greased wires. In a second series of fretting-fatigue tests, this most critical fretting condition was used and kept constant, and the fatigue load was changed. Results show that the fatigue limits of clean and greased wires are equal.
Wave Impact Pressures on U-OWC Breakwater
Authors: Romolo Alessandra , Timpano Bruna , Laface Valentina , Fiamma Vincenzo , Arena Felice 
Published: October 2022

Abstract
A small-scale field experiment was conducted on a U-OWC incorporated into a model of caisson breakwater at the NOEL laboratory of Reggio Calabria (Italy). The U-Oscillating Water Column (U-OWC) or REWEC (REsonant Wave Energy Converter) is a device belonging to the family of OWCs. Such a device is very innovative, being able to absorb a very percentage of incoming sea waves and to produce electrical energy via proper PTO. The focus of the paper has been the analysis of the impact wave loads acting on the modified U-OWC structure during extreme wave events. It has been observed the occurrence of both “quasi-standing wave” loads due to non-breaking waves and “impulsive wave loads” with different wave impacts exerted by a wave breaking against the U-OWC model.
The Likely Cause of Loss of Position for Dynamically Positioned Semi-Submersibles Under Moderate Wave Conditions
Authors: Kaasen Karl E. , Ludvigsen Halgeir , Fonseca Nuno , Lie Halvor , Bjørheim Lars Geir 
Published: October 2022

Abstract
A number of incidents of wave-induced loss of position for dynamically positioned semi-submersible under normal operating conditions have occurred in the Norwegian offshore sector in recent years. A study has been carried out to seek their cause. One hypothesis for the cause has been slamming load from an extremely tall and steep wave that is not effectively counteracted by the DP system due to delays in signal filters and thruster response. Another cause could the loads from a train of tall and steep waves.
A linear single-degree-of-freedom numerical model is made for a vessel with DP. The model is essential in that it represents the basic characteristics of the DP system: State observer/filter and feedback control. The model is used to calculate the frequency response and the impulse response of the dynamically positioned semi-submersible. By calculating extreme impulsive load based on published theory it is established that slamming will not cause great vessel excursion. Still, due to delays, the DP system gives more than twice as large excursion as a mass-spring-damper system with identical restoring stiffness and damping.
Using an advanced model for vessel with DP, three-hour simulations of stochastic vessel response are carried out for five steep wave states of moderate significant height, The likely cause of large vessel excursion is found to be wave-drift. Due to additional viscous loads on the semi’s columns the wave-drift loads will be significantly larger than predicted with potential theory.
Joint-Industry Effort to Develop and Verify CFD Modeling Practice for Predicting Wave Impact
Authors: Pakozdi Csaba , Croonenborghs Eloise , Kim Jang , Peric Milovan , Ducrozet Guillaume , Bouscasse Benjamin , Xu Haihua , Califano Andrea , Akselsen Andreas , Loubeyre Sebastien 
Published: October 2022

Abstract
In 2020, a modeling practice was presented to perform numerical simulation of waves, where waves generated by a numerical wave tank (NWT) were used as input to a CFD simulation. This paper presents an extension of those practices in the context of wave impact on a gravity-based structure (GBS). It focuses on capturing accurate wave loads for a prescribed wave event, reproduced from a measured time series. This modeling practice serves the purpose that if it is followed by a CFD practitioner, the CFD results are reproducible.
The modeling practice is validated for two regular wave cases and one irregular wave event. The validation data are based on experiments performed at MARINTEK in model scale 1:54 with the water depth 2.81m. During the validation the wave time series are compared against model test without and with GBS at scale 1:54. Further, relative wave height time series, global forces and moments acting on the deck as well as slamming forces are compared against model test records. The modeling practice is validated with Simcenter STAR-CCM+ as the main CFD solution but the modeling strategy can be applied to other CFD software.
Thanks to the initialization of the CFD solution with user defined waves (UDW), the NWT-CFD coupling shows two advantages. First, the size of the CFD domain can be reduced to a minimum. Second, it is sufficient to start the CFD simulation shortly before the impact event.