bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical Basis for Prediction of Drilling Fluid Removal in Annuli
Authors: Saasen Arild , Lund Bjørnar , Ytrehus Jan David 
Published: October 2017

Displacement processes are part of several drilling fluid operations. These operations include non-trivial items like changing from water based drilling fluid to oil based or opposite, casing cleaning operations, change to completion fluids or displacement operations during cementing. Among these operations, cementing is the most important and difficult because the scope is to create a permanent barrier and permanent zonal isolation in operations involving only limited volumes of fluids and slurries.
Empirical guidelines have been implemented to improve displacement processes in wells. Analytical and numerical models are frequently used. The models seem to be efficient in predicting pressure losses. However, they seem to be incapable of accurately predict the displacement efficiency. Laboratory experimental results have been evaluated and have been scaled up to for field application with variable success rate. These difficulties are caused by the presence of too many length scales or other dimensional scales.
Data-Driven Real-Time Decision Support and its Application to Hybrid Propulsion Systems
Authors: Reite Karl-Johan , Ladstein Jarle , Haugen Joakim 
Published: October 2017

This paper describes a method for providing real time decision support based on measurements rather than optimizing a mathematical model. The proposed method is thus beneficial for systems for which the modelling would be inaccurate, the dynamics and complexity of the system would make it difficult to optimize in real time, or the risk of returning local minima is not acceptable.
The proposed method is implemented on four fishing vessels. These vessels are complex and give the skipper many choices related to how the vessel is operated. The developed tool advises the crew on in real time on operational decisions, particularly on the use of various diesel electric and diesel mechanic propulsion modes, including decisions such as the use use of shaft generator, direct coupling between main engine and propeller or not, propeller pitch, etc. This will presumably reduce both fuel consumption and emissions of CO2 and NOX.
Some examples of obtainable results from both onshore analyses and the onboard application are presented to demonstrate the methods applicability.
The Study of a New Concept of Flexible Pipe With Carbon Fiber/Epoxy Reinforced Inner Sheath
Authors: Zhou Chongyao , Huang Zhiming , Kang Yongtian , Zhang Dagang , Ye Naiquan , Sævik Svein 
Published: October 2017

Flexible pipe has been widely used in offshore industry for many years. The traditional composite structure of flexible pipe consists of many layers, including multiple metallic layers, such as tensile armor, pressure armor and carcass, as well as nonmetallic layers, such as sheath and liner. Typical flexible pipe is heavy and requires complex manufacturing process, especially pressure armor and carcass manufacturing. Therefore, there is a desire to find a replacement to pressure armor and carcass. With the recent development of a new composite material with lighter weight and higher strength, it now becomes possible. This new composite material is called epoxy compounded carbon fiber (EP/CF). Carbon fiber is 10 times stronger than steel, while it is only 1/5 of the steel weight. Epoxy protects carbon fiber from environmental conditions such as high temperature and corrosion, also bond carbon fiber together and help to redistribute the loading between carbon fibers.
This paper is to present a new concept of flexible pipe by applying the EP/CF material to flexible design. In this new flexible concept, EP/CF is used to strengthen the inner sheath by surface activation treatment of sheath material. This provides excellent hoop strength to resist the inner pressure, hence provides a good replacement to the pressure armor and carcass.
A new FEA analysis method with ABAQUS is also presented in this paper. In the analysis approach, all helix fibers are modelled using predefined beam element, and EP/CF reinforced inner sheath is modeled using laminated composite shell. Nonlinear FEA analysis is carried out in ABAQUS to investigate the tension and bending behavior of flexible pipe with reinforced inner sheath, including the performance of inner pressure resistance, which is one of the key performances. Analysis is also carried out to study the benefit of using EP/CF on outer sheath reinforcement for collision protection. Lastly, the economics and feasibility of this concept are discussed, and conclusions are drawn.
Calculation of VIV Fatigue of Multi-Pipe Systems
Authors: Williams Dara , Kenny Feargal 
Published: October 2017

In various regions of the world offshore oil and gas production and exploration is met with the challenges of operating in extreme currents. These extreme current loads increase the risk of vortex induced vibration (VIV) of the riser system and the associated fatigue damage induced by these vibrations. Regions of particular concern are the Gulf of Mexico where strong loop currents occur, East Africa where the Benguela current dominates and regions offshore South America where strong eddy currents can occur. In order to ensure robust riser design for these regions it is necessary to perform detailed evaluations of the expected VIV response of the global riser system. The assessment of VIV response of steel riser systems is commonplace in the industry and there are well established industry practices in relation to this. In addition there are a number of commercially available VIV analysis tools. Whilst commercially available VIV analysis tools have proved effective in the analysis of long slender structures such as risers there are also a number of limitations in the level of complexity of the model that can be achieved. The analysis approach utilized by these models is based on simplified geometries and linearization of complex non-linear interactions. As a result of these simplifications these analysis tools are not suited to the analysis of non-linear multi-pipe models. Many offshore riser configurations consist of one or more pipe or casing strings enclosed by an outer pipe which is exposed to the environment. In a scenario where VIV of the outer pipe occurs then there will also be a corresponding deflection and curvature transmitted to the inner pipe(s). The displacements and associated stresses of the inner pipe(s) are largely dictated by the response of the outer pipe. Thus for multi-pipe configurations where the inner pipe is not constrained by cement or centralisers (e.g. landing string inside marine riser) the issue arises as to how to calculate the fatigue of the inner strings due to VIV oscillation of the outer string. At the time of writing no standard industry approach exists to address this issue and therefore this paper will outline and demonstrate a proposed approach to address this issue.
The objective of this paper is to outline a novel analysis approach for the calculation of inner string fatigue resulting from VIV of the outer pipe. This proposed methodology combines the benefit of simplified VIV analysis tools with more detailed non-linear global finite element modelling techniques to enable a more comprehensive and accurate assessment of fatigue life of the complete system. The benefits and effectiveness of the proposed method are demonstrated through the analysis of a series of case studies which include landing string fatigue and riser fatigue for deep water applications.
Casing Centralization in Irregular Wellbores
Authors: Skadsem Hans Joakim , Saasen Arild , Håvardstein Stein 
Published: October 2017

Wellbore irregularities can cause excessive mechanical friction forces while attempting to land casing strings, and unfavorable conditions for primary cementing of casing strings. In an eccentric annulus, the fluid velocity is largest in the wide section of the annulus. The drilling fluid on the narrow side of the annulus may be immobilized due to the lower wall shear stress in this section of the annulus. A direct consequence for the primary cementing operation is the potential for having residual drilling fluid between casing and formation, and thereby failing to achieve zonal isolation and adequate mechanical support for the casing.
Casing strings are usually fitted with centralizers at predetermined intervals in order to achieve a minimum degree of centralization in the wellbore and efficient fluid displacement during primary cementing. Centralizer distribution and design are based on assumptions of regular wellbore geometries and often analytical models for estimating lateral casing string displacement in the well. The latter assumption implies that bending moments are not transmitted across centralizers, and may lead to nonconservative centralizer designs. To investigate the effect of irregularity and casing string stiffness, we consider a stiff string model that approximates the casing string as finite beam elements with bending and axial degrees of freedom at each end, thereby accounting for transmission of both axial and bending stresses between elements. In this work, we evaluate wellbore irregularity by inspecting a six-arm caliper log and estimate the cross-sectional shape of the wellbore by cubic spline interpolation between the arms of the caliper tool.
Analyses of the caliper logs indicate that long, continuous strecthes conform to the nominal wellbore size, and that local hole enlargements may be significant. Irregularities are found to be largely symmetric about the wellbore axis, although some examples exhibit elliptic or oval shapes that may conform with local in-situ stress directions. We detail the stiff string model assumptions and implementation for evaluating casing centralization, and demonstrate the approach on model irregularities and on selected caliper log sections. Calculations suggest that bow spring centralizers result in better casing centralization in vertical parts of the wellbore, while large bow spring compression favour rigid centralizers in more inclined parts of the well. Axial compression close to the bottom of the wellbore section leads to a geometric softening effect of the casing, which affects transverse displacement and centralization between centralizers. Higher in the well where the casing is in tension, a geometric stiffening effect reduces transverse displacement. In proximity of washed out and irregular sections, centralization is affected both by placement of the centralizers and a reduction in the restoring capability of bow spring centralizers.
Stresses in Tensile Armour Layers of Unbounded Flexible Risers Loaded With External Pressure: Application to Lateral Buckling Mode
Authors: Caleyron Fabien , Leroy Jean-Marc , Guiton Martin , Duchêne Pascal , Estrier Pascal , Vraniskoski Kristof , Damiens Alexandre 
Published: October 2017

Life6 software, developed by IFP Energies nouvelles, is the local model used by Technip to determine stresses in tensile armour layers of unbounded flexible risers. These stresses and their variations are then used to predict fatigue limits of the dynamically loaded risers. Life6 is based on periodic conditions to reduce the model length, with the assumption that all the tensile armour wires of a same layer share the same kinematics.
This paper firstly presents recent improvements to obtain a better modeling of tensile armour wires kinematics, when the flexible riser loading includes external pressure. New models of the external sheath and the anti-buckling tapes have been developed and implemented in Life6. The results are successfully compared to a Finite Element periodic model.
Applications to lateral buckling prediction of tensile armour layers are secondly presented in the paper. Indeed, in the design of flexible pipelines for offshore field developments, lateral buckling is one of the critical failure modes for the tensile armour wires, being associated with external pressure and flexible pipe cyclic bending. The latest developments made on the modeling of the external kernel of the flexible pipe allow to use Life6 as the basis of the enhancement of the lateral buckling engineering model used by Technip. It has been calibrated and validated against an extensive full scale test data base resulting in a physical, reliable and fast engineering model to predict lateral buckling mode. In accordance with standards, Technip methodology for flexible pipe lateral buckling determination ensures a robust and competitive design.
Fatigue Design Recommendations for Conical Connections in Tubular Structures
Authors: Lotsberg Inge 
Published: October 2017

Conical connections are important structural members for the integrity of most types of welded tubular structures. They are for example used in traditional jacket structures for oil and gas production and in monopiles for support of wind turbines where an optimal design is aimed for. From contact with the industry it is noted that there is uncertainty about the basis for the stress concentration factors for conical connections in design standards for fatigue assessment. This is related to how fabrication tolerances are accounted for and how a transition in thickness from the cone to the tubular or the cylinder should be made to minimise stresses due to thickness transitions and fabrication tolerances.
Analytical expressions for stress concentrations at conical transitions are outlined in this paper to get a better understanding of the thickness of the cone and the cylinder. By a proper basis for fatigue design it is possible to control additional stresses from thickness transitions and fabrication tolerances at these connections.
The Influence of Hold-Back Vessels on the Operation of a DP Drilling Rig: Control System and Stability Analysis
Authors: Huang Alex S. , Tannuri Eduardo Aoun , Queiroz Filho Asdrubal N. , Ianagui André S. S. , Yuba Douglas G. T. , Nogueira Sérgio , Abdalla Thiago C. 
Published: October 2017

Certain maritime operations require the accurate positioning of the vessel, and in order to accomplish that DP (dynamic positioning) systems were developed. It combines the information obtained from sensors with the expected dynamic of the ship to better estimate its actual position and the external forces, and with those information the controller allocates the forces among the available actuators so the vessel keeps a desired position.
In situations where drift of the vessel could cause great harm (human, material or environmental losses) it might be necessary to provide additional safeguards. One possible solution is to connect an AHTS (anchor handling tug supply) to the original DP vessel, in order to complement the forces generated by its thrusters. However as shown by Jensen (2008) and IMCA M 185 (2012), this connection could actually degrade the position keeping ability of the vessel, nullifying the purpose of improving the safety of the operation.
The objective of the present paper is to confirm the hypothesis that the use of hold-back vessels to support DP drilling rigs may degrade the performance of the DP system, causing dynamic instability, and to determine the boundaries of operation under which this phenomenon occurs: sea state, parameters of the vessels and force transmitted by the hold-back vessel.
Firstly, an analytical study of the system was done. It was considered a simplified model of two vessels connected by a cable with two degrees of freedom (one for each vessel), since the force applied by a cable is unidirectional. Using control theory, the limiting stiffness of the cable was determined by analyzing the poles of the system. Considering a catenary model for the connecting cable, it was possible to determine the maximum force that could be transmitted between the vessels without the system becoming unstable. The influence of the Kalman Filter in the stability of the system was also studied.
Those results were then compared and confirmed with fast time dynamic simulations of the system, in which the influence of different environmental conditions were also added to the analysis. To complete the study, real time simulations were done on a full mission simulator, equipped with the original Kongsberg DP system for the drilling rig.
The simplified model showed consistent results, validated by the simulations, demonstrating it can be a useful tool when analyzing the stability of two connected vessels.
A Robust Three-Phase Isenthalpic Flash Algorithm Based on Free-Water Assumption
Authors: Li Ruixue , Li Huazhou Andy 
Published: October 2017

Multiphase isenthalpic flash calculations are often required in compositional simulations of steam-based enhanced oil recovery methods. These flash calculations are challenging in the narrow-boiling regions and in the determination of the correct number of existing phases. Based on the free-water assumption that the aqueous phase is pure water, a robust and efficient algorithm is proposed to perform isenthalpic three-phase flash calculations in this work. Multiphase equilibria can be considered by this algorithm, including single-phase equilibria, two-phase equilibria, and three-phase vapor-liquid-aqueous equilibria.
Isenthalpic flash is a type of flash calculation conducted at given pressure and enthalpy for a feed mixture. In the proposed algorithm, assuming the feed is stable, the temperature is first determined by solving the energy conservation equation. Then the stability test on the feed mixture is conducted at the calculated temperature and the given pressure. If the mixture is found unstable, the two-phase and three-phase vapor-liquid-aqueous isenthalpic flash calculations can be simultaneously initiated without resorting to stability tests. To achieve simultaneous flashes, the outer loop is used to update the temperature by solving the energy conservation equation. The inner loop is used to obtain phase fractions and compositions by performing a three-phase free-water isothermal flash. Note that a two-phase isothermal flash will be initiated if an open feasible region in the phase fractions appears in any iteration during the three-phase isothermal flash or any of the ultimately calculated phase fractions from the three-phase flash do not belong to [0,1]. Negative flash is allowed in the three-phase free-water isothermal flash.
A number of example calculations for water/hydrocarbon mixtures are carried out to test the robustness of the proposed algorithm. At low to medium pressures, a good agreement can be achieved between the results obtained by this algorithm and those obtained by the conventional algorithm. This algorithm performs well for the narrow-boiling regions, for example, the three-phase vapor-liquid-aqueous equilibrium region encountered for the water/hydrocarbon mixtures. During the iteration, the new algorithm can readily handle the appearance and disappearance of phases in the inner loop as temperature updates in the outer loop. The number of stability tests involved in the new algorithm is significantly reduced, helping to boost its computational efficiency.
Near Field Expression of Ship Wave Resistance by Yeung’s Method
Authors: Tsubogo Takashi 
Published: October 2017

The ship wave resistance can be evaluated by two alternative methods after solving the boundary value problem. One is the far field method e.g. Havelock’s formula, and another is the near field method based on direct pressure integration over the wetted hull surface. As is well known, there exist considerable discrepancies between wave resistance results by far field method and by near field method.
This paper presents a Lagally expression in consistency with Havelock’s formula. In order to derive the Lagally expression, the symmetry of Havelock’s Green function is used in the same manner as Yeung et al (2004). Another expression to examine the relation with water pressure integrations or to ensure physical consistency is also derived by slightly deforming that expression. Some numerical comparisons of wave resistance of Wigley, KCS and KVLCC2 models among by Havelock’s formula, some direct pressure integration methods and present two new near field expressions, are shown to demonstrate consistency numerically.
Development of a Simulation Tool Coupling Hydrodynamics and Unsteady Aerodynamics to Study Floating Wind Turbines
Authors: Leroy Vincent , Gilloteaux Jean-Christophe , Philippe Maxime , Babarit Aurélien , Ferrant Pierre 
Published: October 2017

Depending on the environmental conditions, floating Horizontal Axis Wind Turbines (FHAWTs) may have a very unsteady behaviour. The wind inflow is unsteady and fluctuating in space and time. The floating platform has six Degrees of Freedom (DoFs) of movement. The aerodynamics of the rotor is subjected to many unsteady phenomena: dynamic inflow, stall, tower shadow and rotor/wake interactions. State-of-the-art aerodynamic models used for the design of wind turbines may not be accurate enough to model such systems at sea. For HAWTs, methods such as Blade Element Momentum (BEM) [1] have been widely used and validated for bottom fixed turbines. However, the motions of a floating system induce unsteady phenomena and interactions with its wake that are not accounted for in BEM codes [2]. Several research projects such as the OC3 [3], OC4 [4] and OC5 [5] projects focus on the simulation of FHAWTs.
To study the seakeeping of Floating Offshore Wind Turbines (FOWTs), it has been chosen to couple an unsteady free vortex wake aerodynamic solver (CACTUS) to a seakeeping code (InWave [6]). The free vortex wake theory assumes a potential flow but inherently models rotor/wake interactions and skewed rotor configurations. It shows a good compromise between accuracy and computational time.
A first code-to-code validation has been done with results from FAST [7]on the FHAWT OC3 test case [3] considering the NREL 5MW wind turbine on the OC3Hywind SPAR platform. The code-to-code validation includes hydrodynamics, moorings and control (in torque and blade pitch). It shows good agreement between the two codes for small amplitude motions, discrepancies arise for rougher sea conditions due to differences in the used aerodynamic models.
Deep Water XLPE Cable With Aluminum Conductor: Risk of Stress Induced Electrochemical Degradation (SIED)
Authors: Bengtsson Magnus , Floden Randi , Clasen Torunn Lund 
Published: October 2017

One of the challenges with cables in deep waters is the high topside tension caused by the weight of the cable and the risk of overloading the conductor. Keeping the cable weight as low as possible is therefore a key parameter to reach deep waters. One way to reduce the cable weight is to replace the copper conductor in the cable with an aluminium conductor.
When using aluminium conductor in a wet design XLPE cable (no water barrier) there is a risk of local corrosion of aluminium that forms porous structures in the inner semiconductor, leading to accelerated ageing of the XLPE insulation. This phenomenon is known as Stress-Induced Electrochemical Degradation (SIED). SIED has so far only been seen in service-aged cables, which had been exposed to external mechanical damage causing water penetration in the conductor. It has also been found that the deterioration of the inner semicon is more severe when the cable is mechanically stressed. In order to learn more about the risk of SIED in a wet XLPE cable an extensive ageing test program has been carried out. This paper summarizes the results from this testing.