bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metocean Design Criteria for Deep Water Offshore Systems
Authors: Drago Michele , Mattioli Matteo , Quondamatteo Federico 
Published: October 2015

In the last decades the off-shore hydrocarbon extraction industry has extended its field of activities in very deep waters up to more than 2000 m. Extraction and production systems can vary between complete subsea development with export pipelines to on-shore treatment plants and surface development by means of surface units (SSFU) connected to subsea wells by risers and anchored by mooring systems which extend through the whole water column. For exclusively subsea developments, including sealines, the metocean design data and criteria to be developed and the applicable methodologies to derive them are well established. Univariate theory is usually applied in order to quantify the risk of failure due to (extreme) sea conditions.
The surface developments and the connections through the water column (e.g. risers, moorings) are newly challenging aspects. They could suffer from severe damages due to the occurrence of critical combinations of different variables during a single sea storm:: thus, it may be important to consider the joint occurrence of different forcing conditions (i.e. multivariate analysis).
The present manuscript provides a simplified methodology in order to carry out a sensible multivariate analysis of the contemporary data such as wind, waves and current.
Three different cases are analyzed: i) the correlation of extremes of different variables (wind, wave and current), ii) the extreme profiles of current and iii) the current profile climate. A practical case study is illustrated throughout the paper.
Establishing Operational Fatigue Limits for Short-Term Riser Operations
Authors: Sundararaman Shankar , Cerkovnik Mark , Ferreira Luiza , Ward Phil 
Published: October 2015

Drilling and intervention risers are widely used for oil and gas production in deep as well as shallow waters in oil fields around the world for subsea operations. The risers come in a diverse array of configurations, some of which may be challenged by fatigue if operated in high currents or seastates. The suitability of the selected riser and the operating limits are assessed by conducting strength and fatigue analysis based on design codes such as API RP 2RD, [7], API RP 16Q, [9], and API RP 17G, [10].
Typically, drilling and intervention activities are conducted for short periods of time but used repetitively. The codes are clear about the return period of the design environmental event which must be checked to insure safe operation with respect to strength; however, assessment of fatigue integrity can be more difficult to determine. The allowable fatigue operating environment should account for the ability to disengage, the time required to disengage, the damage rates in particular seastates, prior accumulation of fatigue damage, and variations in soil, tension and internal fluid weights.
In this paper, an orderly method of establishing the allowable fatigue operation limits for drilling and intervention risers is presented based on Monte Carlo simulations along with a case study implementing the methodology in a shallow water environment. To illustrate this concept, a riser with wellhead and conductor system is assessed and is subjected to directional loading from several long-term seastates. The variation in effects is studied by doing fatigue analysis for different durations: 3 days, 1 week, 3 months, 1 year and 10,000 hours.
Integrating Structural Health and Condition Monitoring: A Cost Benefit Analysis for Offshore Wind Energy
Authors: May Allan , McMillan David , Thöns Sebastian 
Published: October 2015

There is a large financial incentive to minimise operations and maintenance (O&M) costs for offshore wind power by optimising the maintenance plan. The integration of condition monitoring (CM) and structural health monitoring (SHM) may help realise this. There is limited work on the integration of both CM and SHM for offshore wind power or the use of imperfectly operating monitoring equipment. In order to investigate this, a dynamic Bayesian network and limit state equations are coupled with Monte Carlo simulations to deteriorate components in a wind farm.
The CM system has a ‘deterioration window’ allowing for the possible detection of faults up to 6 months in advance. The SHM system model uses a reduction in the probability of failure factor to account for lower modelling uncertainties.
A case study is produced that shows a reduction in operating costs and also a reduction in risk. The lifetime levelised costs are reduced by approximately 6%.
On the Effect of Work Hardening on Strain-Localization and Fracture Initiation in Collision Simulations
Authors: Storheim Martin , Amdahl Jørgen 
Published: October 2015

The exact material behavior is not known a priori in a collision event involving ships or offshore structures due to the vast number of ships with different materials and the variation in material properties from manufacturer to manufacturer and from material batch to batch. Hence, assumptions are necessary when calculating the resistance to a collision event.
A common starting point can be the requirements to the material quality set by regulatory bodies, often giving a range of allowable yield stress, ultimate stress and elongation at ultimate stress. This leaves the actual hardening response to the engineer.
This paper investigates the consequences of different choices of plastic work hardening calibrated to the same assumption of yield stress, ultimate stress and elongation at failure. Non-linear finite element analysis of ship collision is utilized. The findings are discussed, and some recommendations given.
The simulations shows that the collision response is highly sensitive to the actual material response; initial yield stress, tensile strength, strain at tensile strength and the rate of work hardening are all essential in this context.
Review of Steel Lazy Wave Riser Concepts for North Sea
Authors: Felisita Airindy , Gudmestad O. T. , Karunakaran Daniel , Martinsen Lars Olav 
Published: October 2015

The Steel Catenary Riser (SCR) is considered a favorable solution for deepwater development. However, the application of SCRs in harsh environments is challenging, mainly due to fatigue at the touch down zone. One of the solutions to improve SCRs’ fatigue performance is the application of buoyancy modules in order to achieve a Steel Lazy Wave Riser (SLWR) configuration.
This paper presents a parametric study of a SLWR system for application in deepwater and harsh environments. The selected harsh environment is the seas within the Norwegian Continental Shelf. The main geometric variations are the length of the buoyancy section and the dimension of the buoyancy modules. These variations result in riser configurations with different riser’s wave heights. The term ‘riser’s wave height’ refers to the vertical distance between the lowest point at sagbend and the highest point at hogbend of a riser. The analysis works are performed using Orcaflex.
The results show that the application of buoyancy modules help to improve the performance of a steel catenary riser for application in a harsh environment. The dimension of a riser’s wave shape proves to be an important factor that controls strength and fatigue performance of a riser. Lazy wave riser configurations with larger and better defined wave shapes have lower stress utilizations and lower fatigue damage, while riser configurations with smaller wave shapes have higher stress utilizations and higher fatigue damage. This is due to lazy wave configurations with higher wave shape have better capability to absorb the dynamic loads.
On Probabilistic Fracture Assessment of Defective Pipeline Based on Target Failure Probabilities
Authors: Lee Jae-Bin , Kim Ki-Seok , Cho Woo-Yeon , Shim Sang-Hoon , Huh Nam-Su 
Published: October 2015

This paper investigates the priorities as well as the safety factors of each assessment variable for a defective pipeline based on a partial safety factor concept considering the target failure probabilities during operating period of components of interest.
For this, firstly wall-thinned pipeline under internal pressure is considered, which is important in fitness-for-service assessment of corroded pipeline. For the analysis, scatters in the applied pressure, mechanical properties and geometries of wall-thinned pipeline are considered using normal and log-normal distributions. In addition, partial safety factors of a circumferential through-wall cracked pipeline subjected to global bending moment are also evaluated based on the elastic-plastic fracture mechanics. In this case, scatters in the applied bending moment, mechanical and fracture properties are considered based on normal and log-normal distributions.
More importantly, two different deterministic integrity assessment methods are applied to wall-thinned pipeline and two different estimation methods of elastic-plastic J-integral are applied to circumferential through-wall cracked pipeline to evaluate the partial safety factors. Resulting values of partial safety factors are calculated using both the advanced first-order second moment method (AFOSM) and the second-order reliability method (SORM). Moreover, the effects of statistical distributions and variations of standard deviations of assessment variables on the partial safety factors are also demonstrated.
Implementation of a Nonlinear Riser-Soil Interaction Model for Abaqus
Authors: Akula Venkata M. K. , Datye Deepak 
Published: October 2015

For a steel catenary riser system, the touch-down point is often a concern as it can influence the structural response of the riser and its performance. Although, riser configurations can be designed to withstand wave loading, internal pressure, external pressure, and thermal loads; the design of risers taking into account the interaction between the riser and the soil, with cycles of contact and separation, still remains challenging. More specifically, when the riser contacts the seabed surface, it penetrates into the soil material. This penetration can cause suction-type behavior when the riser moves away from the surface. Further, it causes permanent deformation in the soil so the riser has to traverse additional distance prior to re-contacting the seabed surface. For formulating a robust riser design using the finite element method, accurate modeling of this nonlinear riser-soil interaction is needed.
In the majority of situations, risers are modeled with beam elements. This is an efficient approach considering that a riser-pipeline system can be several thousand meters in length and using shell or brick elements for modeling such a system becomes computationally expensive. In addition, the seabed surface is often modeled as a rigid surface. The riser-soil interaction behavior is then incorporated into the finite element analysis either by defining springs at the contacting nodes or by modifying the normal contact stiffness for the interaction. However, these methods do not entirely capture the nonlinear riser-soil interaction behavior.
In this paper, we discuss the modeling of the nonlinear riser-soil interaction through the use of a user subroutine that runs in conjunction with a finite element analysis using Abaqus. This subroutine is intended to provide a special contact interaction property definition between the riser and the seabed. This contact property definition focuses primarily on the normal behavior although frictional resistance is also considered. The results of the simulation and the insights gained are included.
Experimental Studies of Pressure Loss in Inclined Pipe in Slurry Transport for Subsea Mining
Authors: Masanobu Sotaro , Takano Satoru , Fujiwara Tomo , Kanada Shigeo , Ono Masao 
Published: October 2015

For subsea mining, the estimation of pressure loss in the pipe of lifting system and the flexible pipe to connect the mining tool and the lifting system is important to design the mining system. The configuration of flexible pipe is expected to have an inclined part.
In the present paper, the authors carried out the experiment to measure the pressure loss in inclined pipes using alumina beads to investigate the effect of inclination angle of pipe on the pressure loss. Furthermore, a mathematical model to estimate the pressure loss in inclined pipes was proposed and validated through the experiments. As the result of the validation, it was confirmed that the proposed model could be applied to the pressure loss estimation in inclined pipes.
A Revised Methodology for the Calculation of MODU Watch Circles
Authors: Quigley Conor , Williams Dara 
Published: October 2015

As the industry continues to push the boundaries of offshore exploration into deeper water depths and harsher environments there is an increased need to ensure the integrity of both the drilling riser and wellhead in the event of loss of station-keeping in dynamically positioned (DP) rigs. In order to determine vessel limiting operating/alert offsets it is necessary to carry out a vessel drift-off analysis which predicts the vessel drift-off speed and direction in the event of a DP failure.
This analysis is typically performed for a limited combination of environmental conditions (usually collinear wind, wave and current) and will generally assume a vessel position that is directly above the wellhead. Whilst the results of the standard drift-off analysis, and associated drift-off plots, are useful in determining expected drift-off speed and feasibility of the emergency disconnect sequence (EDS), the outputs are of little operational use to the rig personnel in determining allowable operational/alert offsets for day to day operations. As the vessel is rarely located directly above the wellhead and environmental conditions can vary significantly in both direction and magnitude over the drilling campaign a more comprehensive analysis methodology and set of load cases is required in order to develop useful inputs to the well specific operating guidelines (WSOG).
The current standard industry approach is to generate drilling riser operability envelopes independently of drift-off curves and thus recommended operating offsets do not account for drift-off speed, reaction times or EDS times. This can lead to a potential lack of conservatism in WSOG. In order to avoid this lack of conservatism in calculation of operating offsets a coupled steady-state/transient response analysis approach is required to ensure that a DP failure event at limiting operational offset does not lead to damage to the wellhead or riser system.
A new revised methodology for the calculation of allowable operating windows and associated alert offsets is presented in this paper. This new methodology couples both the steady state operating limits of the vessel and the transient system response during a drift-off, due to DP failure, in order to present a comprehensive go/no-go operability chart of allowable offset vs. environment for use as input to the WSOG.
Ethylene Glycol as Gas Hydrate Stabilising Substance
Authors: Schulz Anne , Strauß Heike 
Published: October 2015

Gas hydrates are solid substances consisting of water and gas which are stable under high pressure and low temperature conditions. After Davy discovered chlorine hydrate in 1810, gas hydrates from natural gas were found to be the reason for gas pipeline plugging in 1934 by Hammerschmidt. In 1965, the Russian scientist Makogon discovered natural gas hydrate deposits. This was the beginning of research in the geological occurrence of the gas hydrates.
Today, hundreds of gas hydrate wells for exploration have been drilled all over the world in the permafrost and deep sea regions. Several big projects for gas hydrate research and exploration have been financed by Japan, India, Korea, China and the USA. It is assumed that the amount of carbon in natural gas hydrates is twice the amount present in oil, gas and coal together. This makes them interesting as a future energy source. To drill into horizontal layers filled with gas hydrates in the pores, directional wells are needed.
To achieve an adequate cutting transport, a high performance drilling fluid has to be used instead of sea water. The drilling fluid must be able to keep the gas hydrate reservoir stable while drilling and prevent the formation of secondary gas hydrates in the liquid. Moreover, the gas hydrate cuttings should not dissociate on their way to the surface. To avoid altering of the drilling fluid due to water and gas produced as a result of gas hydrate dissociation, cuttings should be kept stable to separate them from the fluid like any other rock cuttings by the surface equipment.
To prevent gas hydrate formation, thermodynamic inhibitors, like salt, glycols or methanol are used. Also, kinetic inhibitors are added to the drilling fluid to prevent gas hydrate agglomeration and formation for a period of time. Well known kinetic inhibitors are polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and polyvinylcaprolactam (PVCap).
Although ethylene glycol (EG) is seen as a thermodynamic inhibitor for gas hydrates, it is shown in this study that it is able to stabilize methane hydrate significantly. For the investigation, a high pressure cell with pressures up to 8.5 MPa was used. The equilibrium point of methane hydrate was detected. Solutions with PVP, PEG, hydroxyethylcellulose (HEC), Sodium dodecyl sulfate (SDS) and a kinetic inhibitor containing EG were tested (concentrations from 1 to 10 wt.‰). PVP, PEG and HEC could not stabilize gas hydrates at the test condition. SDS showed both a stabilizing and promoting effect. EG can significantly stabilize gas hydrates.
Impacts of Cold Climate Environmental Conditions on a Riser System Design and Installation
Authors: Orimolade Adekunle Peter , Gudmestad Ove Tobias 
Published: October 2015

Interests in exploration and production of oil and gas in cold climate areas has increased in recent times. This can be attributed to the continual depletion of reserves in mature fields, and recent discoveries of large quantities of oil and gas in the cold climate region, including the more recent discovery of the Alta Reservoir, in the Barents Sea. However, marine operations in this region are faced with challenges resulting from its arctic conditions.
Knowledge of the physical environment is important in designing offshore structures, and in planning, and executing marine operations. Selection of a suitable field development concept may be influenced by the probability of occurrence of rare events, such as drifting icebergs. Furthermore, occurrence of mesoscale phenomenon such as polar low pressures may adversely affect planned marine operations. In addition, uncertainties in weather forecasting will reflect on the available weather window to perform installation and interventions works.
This paper presents some of the challenges in designing and planning for marine operations in the cold climate region. A possible field development concept for the open water areas of the Norwegian sector of the Barents Sea is discussed. The current research work considers the need for further assessment of the probability of occurrence of drifting icebergs as of importance when selecting field development concept. The Floating Production Storage and Offloading (FPSO) is proposed, and this should be designed with an internal turret system that can be disconnected and reconnected. Some of the challenges associated with riser systems design when considering a turret system with the capability to disconnect and reconnect are discussed.
This paper also propose the use of ensemble forecasts as an alternative to the use of alpha factors to estimate operational weather window when planning for marine operations in the Barents Sea. The unpredictability nature of the environmental conditions, especially in the early winter is considered a challenge to marine operations.
Flexible Spools Solution for Hybrid Risers Base for Green Fields Developments
Authors: Tarbadar S. , Legeay S. , Bonnissel M. , Nossa O. , Karnikian A. 
Published: October 2015

Rigid spools are commonly used at the riser base of hybrid riser systems such as STTRs (Single Top Tensioned Risers) or BHORs (Bundle Hybrid Offset Risers) for the deep water oil fields. Rigid spools design is critical and governed by numerous operating constraints such as dynamic loadings (due to motion of the vertical riser, Vortex Induced Vibration, slugging, etc.), soil properties and soil/spools/structures interaction.
Recent surveys on existing brown fields have highlighted unexpected issues on existing rigid spools. To solve these issues, an innovative flexible spool solution has been developed, combining unbonded flexible pipe structures in a “steep wave” configuration to accommodate the riser motions and FLET (Flowline End Termination) excursions avoiding soil deterioration and preventing unexpected spool behavior which could ultimately jeopardize its integrity.
A steep wave configuration solution can be introduced with distributed buoyancy over the flexible spools length. This design allows a direct connection between the riser base assembly and the flowline termination, solving the embedment issue and easing accommodation of the hybrid riser motions.
This paper describes the recent issues with rigid spools design and describes the solutions developed with flexible spool configurations to provide a more reliable riser base spools system for green fields.
Experimental Study on the Effect of Gas Hydrate Content on Heat Transfer
Authors: Meindinyo Remi-Erempagamo T. , Bøe Runar , Svartås Thor Martin , Bru Silje 
Published: October 2015

Gas hydrates are the foremost flow assurance issue in deep water operations. Since heat transfer is a limiting factor in gas hydrate formation processes, a better understanding of its relation to hydrate formation is important.
This work presents findings from experimental study of the effect of gas hydrate content on heat transfer through a cylindrical wall. The experiments were carried out at temperature conditions similar to those encountered in flowlines in deep water conditions. Experiments were conducted on methane hydrate, Tetrahydrofuran hydrate, and ethylene oxide hydrate respectively in stirred cylindrical high pressure autoclave cells. Methane hydrate was formed at 90 bars (pressure), and 8°C, followed by a cooling/heating cycle in the range of 8°C → 4°C → 8°C. Tetrahydrofuran (THF) and ethylene oxide (EO) hydrates were formed at atmospheric pressure and system temperature of 1°C in contact with atmospheric air. This was followed by a heating/cooling cycle within the range of 1°C → 4°C → 1°C, since the hydrate equilibrium temperature of THF hydrate is 4.98°C in contact with air at atmospheric pressure. The experimental conditions of the latter hydrate formers were more controlled, given that both THF and EO are miscible with water.
We found in all cases a general trend of decreasing heat transfer coefficient of the cell content with increasing concentration of hydrate in the cell, indicating that hydrate formation creates a heat transfer barrier. The hydrate equilibrium temperature seemed to change with a change in the stoichiometric concentration of THF and EO. While the methane hydrate cooling/heating cycles were performed under quiescent conditions, the effect of stirring was investigated for the latter hydrate formers.