bluuebunny/crossref_metadata_2025 huggingface dataset:
The Next Generation Technology for Automatic Inflow Control
Authors: Grüner Vegar , Rinde Trygve , Lager Thorleif , Killie Rune , Solberg Tron , Bakli Mikkel
Published: October 2017

Breakthroughs of water and/or gas in production wells may have direct consequences for the production rates and overall field recovery. Multiple technologies have recently been developed to autonomously control inflow from the reservoir. Common to all these technologies is that new limitations are introduced which may have a negative impact on the well. This paper presents the design process for the next generation inflow control system and introduces new requirements for such completions.

Traditional Passive Inflow Control Devices (ICD) are designed to act in a preventive manner by setting up a somewhat more even inflow profile along the reservoir section and thereby delay the breakthrough of gas or water. More recently, several new initiatives have been presented which will operate autonomously, with an ambition to choke back unwanted production. Common to these technologies is that they are primarily dependent on viscosity differences between the reservoir fluids.

In the work presented in the following, the design process has identified the following requirements for the next generation autonomous inflow control system:

• easy to install completion

• robust in design and functionality

• Improve clean-up of mud and completion fluids

• independent of fluid viscosity

• negligible pressure drop during normal production

• allows back-flow of fluids

In this paper the results from an ongoing development of a new design inflow control system, independent on differences in fluid viscosities is presented, which fulfills above requirements. This system is based on a valve, which blocks, or restricts, production of unwanted water or gas, and re-opens for production if oil comes back. It can be designed to stop water/gas production at a predetermined WC/GOR. Furthermore, it ensures efficient clean-up along the full length of the reservoir section and is insensitive to exposure to mud, particles and filter cake. The installation of this system will not restrict any future well operations and it can be designed with a fail-safe option.

The new system represents a great technological improvement which will ensure a robust, economical and fail safe design as well as a simplification of inflow design process, since it will work irrespective of local productivity, pressure and flow rate. Hence, removing the operational envelopes on which other technologies must be designed for to be able to work properly.
Investigation of Pressure Losses in Eccentric Inclined Annuli
Authors: Rushd S. , Sultan R. A. , Rahman A. , Kelessidis V.
Published: October 2017

Accurate pressure drop estimation is vital in the hydraulic design of annular drillholes in Petroleum Industry. The present study investigates the effects of fluid velocity, fluid type, fluid rheology, drillpipe rotation speed, drillpipe eccentricity and drillhole inclinationon on pressure losses with the presence of cuttings using both experiments and computational fluid dynamics (CFD). The eccentricity of the drillpipe is varied in the range of 0 – 100% and it rotates about its own axis at 0 – 150 rpm. The diameter ratio of the simulated drillhole is 0.56 and it is inclined in the range of 0 – 15°. The effects of fluid rheology are addressed by testing power law and yield power law fluids. Both of the laminar and turbulent conditions are experimentally tested and numerically simulated. Experimental data confirmed the validity of current CFD model developed using ANSYS 16.2 platform. The goal of the current work is to develop a comprehensive CFD tool that can be used for modeling the hydraulic conditions associated with hole cleaning in extended reach drilling.
On Tower Top Axial Acceleration and Drivetrain Responses in a Spar-Type Floating Wind Turbine
Authors: Rasekhi Nejad Amir , Bachynski Erin E. , Moan Torgeir
Published: October 2017

Common industrial practice for designing floating wind turbines is to set an operational limit for the tower-top axial acceleration, normally in the range of 0.2–0.3g, which is typically understood to be related to the safety of turbine components. This paper investigates the rationality of the tower-top acceleration limit by evaluating the correlation between acceleration and drivetrain responses. A 5 MW reference drivetrain is selected and modelled on a spar-type floating wind turbine in 320 m water depth. A range of environmental conditions are selected based on the long-term distribution of wind speed, significant wave height, and peak period from hindcast data for the Northern North Sea. For each condition, global analysis using an aero-hydro-servo-elastic tool is carried out for six one-hour realizations. The global analysis results provide useful information on their own — regarding the correlation between environmental condition and tower top acceleration, and correlation between tower top acceleration and other responses of interest — which are used as input in a decoupled analysis approach. The load effects and motions from the global analysis are applied on a detailed drivetrain model in a multi-body system (MBS) analysis tool. The local responses on bearings are then obtained from MBS analysis and post-processed for the correlation study. Although the maximum acceleration provides a good indication of the wave-induced loads, it is not seen to be a good predictor for significant fatigue damage on the main bearings in this case.
An Engineering-Model for Extreme Wave-Induced Loads on Monopile Foundations
Authors: Hansen Hans Fabricius , Kofoed-Hansen Henrik
Published: October 2017

An extension of the classical Wheeler’s method is here presented and validated. Just as the Wheeler’s method, it relies solely on the measurement of surface elevation in a point to make predictions of the wave induced loads.

These measurements may be made in the field, but more often they will be generated in a laboratory wave basin. The classical Wheeler stretching plus Morison load model is augmented by a slamming load model for steep near-breaking and breaking waves, based on work published earlier by Nestegård et.al. (2004). The new model thereby spans the entire range from non-breaking waves to severely breaking overturning waves with a gradual transition. The model has been validated against surface elevations and wave loads measured in a laboratory wave tank and is found to reproduce wave load distributions over a range of sea state conditions well.

Examples are given for typical design sea state conditions for offshore wind turbines at exposed locations in Northern Europe. The loads are compared to loads obtained using the stream function wave theory in combination with the Morison’s equation. The stream function wave theory loads are found to generally be lower than the loads predicted using the simple wave load model presented here. This is the case even for mildly non-linear non-breaking waves but becomes much more pronounced for steep near-breaking and breaking waves. Another striking feature of the comparison to regular wave theory is the different distribution of loads. The stream function loads below still water level are often higher than the loads from the simple model, but much lower than the simple load model loads above still water level.
Investigations on the Damage Potential of Drilling Fluids: HT/HP-Return-Permeability Tests Under Dynamic Conditions
Authors: Freese Carsten
Published: October 2017

In view of the increasing scarcity of energy resources, wells are being drilled to progressively greater depths for the production of liquid and gaseous hydrocarbons. Economical exploitation of these HT/HP reservoirs is possible only with the application of drilling and completion methods which do not damage the formation. Here, the reservoir-saving exposure of these deposits is an essential contribution.

The damage potential of drilling fluids and treatment fluids is usually assessed on the basis of return permeability (RP) tests. An impairment of the effective rock permeability through appropriate candidate fluids (drill in fluids, etc.) can be measured with special laboratory tests. In addition to the RP-Tests further investigations should be made to estimate the formation damage such as high-resolution digital photography, mercury porosimetry, scanning electron microscopy as well as microsection analyses.

Within the framework of the German Society for Petroleum and Coal Science and Technology a project was carried out to evaluate common formation damage test facilities and to define the “best practice” meeting the requirements of RP-measurements under borehole-like conditions. After a thorough evaluation an advanced HT/HP facility for formation damage testing was designed and built. By using of this set-up, systematic return-permeability tests were performed under dynamic conditions for temperatures up to 180 °C, for a flow pressure up to 250 bar, and a mantle pressure up to 350 bar.

This paper presents results from a study on the filtration and formation damage behaviour of drilling fluids under variation of the concentration and of the weighting material particle size distribution. Furthermore, promising results from changing dynamic and static filtration experiments are discussed.
Dynamic Averaging Method to Detect Sea Surface Current From Radar Images
Authors: Wijaya Andreas P.
Published: October 2017

One important parameter in reconstructing and predicting the sea surface elevation from radar images is the surface current. The common method to derive the current is based on 3DFFT with which the (absolute) frequency is derived from a series of images and is fitted to the encounter dispersion relation that consist of the intrinsic exact dispersion relation for linear waves with an additional term that contains the current velocity to be found. The derived dispersion relation will be inaccurate because the images contain many inaccuracies from noise, shadowing, and other radar effects. This paper proposes an alternative method to determine the surface current. Following the method of the Dynamic Averaging and Evolution Scenario (DAES) as presented in [1], the idea is to choose the current velocity that minimizes the difference between an image at a previous time that has been evolved to the time of another image. In order to reduce inaccuracies, an averaging procedure over various images is applied. The method is tested on synthetic data to quantify the accuracy of the results. The robustness of the method will be investigated for several cases of different current parameters (speed and direction) for ensembles of seas with different peak frequency of characteristic sea states.
On the Numerical Modeling of Slug and Intermittent Flows in Oil and Gas Production
Authors: Nieckele Angela O. , Carneiro João N. E.
Published: October 2017

Recent advances on the modeling of two-phase flows in pipes have shown that the accurate modeling of Two-Fluid equations allow the dynamic simulation of various regimes within a single numerical framework, diminishing the empiricism associated with the flow-pattern dependent closure relations. Such “Regime-Capturing” approaches have been traditionally called “Slug-Capturing”, as a reference to dynamic simulations of stratified-to-slug transition. In this paper, we will outline several examples of applications, ranging from horizontal stratified wavy, slug and annular flows, to vertical annular and intermittent flows. Vertical flow has been a bottleneck in Slug Capturing due to ill-posedness of the Two-Fluid Model. Ill-posedness of the model equations will be briefly addressed along with different regularization methods and stabilizing terms based on physical behavior, such as shape profile factors and dynamic pressure contributions. In order to numerically solve the governing system of equations, the finite volume method is employed with Upwind and second order TVD spatial discretization schemes, along with first order time discretization.

Flow parameters such as temperature and pressure drop are determined as well as film thickness and wave characteristics of both annular and stratified flow, and slug velocity, length and frequency in slugging cases. Comparison with experimental data for annular, slug and stratified flows, with different fluids and pipeline configurations are presented, illustrating the good performance of the methodology.
Study of Local Ice Loads Measured at Norströmsgund Lighthouse
Authors: Zvyagin Petr , Ziemer Gesa
Published: October 2017

It is believed that ice loading can be a stationary process at least sometimes during the state of continuous brittle crushing. Confidence in the distribution law, stationarity in time, and autocorrelation function of local ice loads is the key factor for assessment of such loads and their successful simulation. Good understanding of the load process on the level of a single transducer record can be helpful in future analysis and simulation of loads on wider contact areas.

In this paper local loads, simultaneously measured by two middle subpanels at the Norströmsgrund lighthouse in March 2001, are studied. Stationary time series of lognormal origin of 50 seconds duration are extracted from both of the subpanel records. From the studied data, stationarity was not observed simultaneously at different subpanels. The correlation of one stationary subpanel record with simultaneous record of the other subpanel found to be weak.

A simple function with good fit to the observed autocorrelation curve of stationary load fragments is suggested. The findings are compared with parameters obtained for local loads in previous studies. A transition from autocorrelation function for raw lognormal data to autocorrelation function of logarithmic normal data is performed.
The Potential for Non-Conservative Results From the Probabilistic Fracture Mechanics Analyses Is Assessed Based on the Collected Observation of Fatigue Cracks in Offshore Steel Structures
Authors: Vårdal Ole Tom
Published: October 2017

In structural integrity management, it is essential to know the fatigue crack growth potential. The lessons learned from use of refined fatigue analyses, fracture mechanics and probabilistic methods for platforms in-service are presented. For ageing offshore units of semi-submersible design, the inspection history of more than 20 000 NDT inspections and detection of close to 1000 fatigue cracks, are used in this study. These experience data are used to assess the potential for Non-conservative estimate for the fatigue crack growth potential.
Corrosion Prognosis: Maritime Structural Performances in Service Environments
Authors: Wang Yikun , Downes Jon , Wharton Julian A. , Shenoi R. Ajit
Published: October 2017

For marine platforms, assessing the structural resilience in a corroded condition is vital for both design and maintenance practices. With the development of computational and experimental methods for structural analysis, the accuracy of the structural response prediction relies on a better understanding of the material degradation process. However, a realistic estimate of corrosion is inherently a complex undertaking. Corrosion of even a single form can often involve multiple stages, each of which has different steps across several geometric scales; corrosion systems are often multi-layered and involve geometric complexities; the mechanical factors (stress/strain distributions) could affect the corrosion initiation and kinetics. These complexities have resulted in scientific barriers to the advancement of a corrosion prognosis that forecasts damage accumulation, as well as a computational realization of the corrosion-structural analysis. This paper reviews the numerical and experimental work that the authors have done, including the development of nonlinear finite element models to assess the behavior of damaged steel ship structures, full-field experimental verifications, application of the mechano-electrochemical theory and in situ tensile-corrosion tests. It is intended that the outcome of this research will be the establishment of a systematic multi-scale multi-physics experimental and numerical protocol for predicting aged structural resilience.
A CFD Investigation on the Effect of the Air Entrainment in Breaking Wave Impacts on a Mono-Pile
Authors: Tomaselli Pietro D. , Christensen Erik Damgaard
Published: October 2017

In impacts of breaking waves on offshore structures, it is still not well-known how the air entrainment phenomenon affects the exerted loads. In this paper, a developed CFD solver capable of simulating the air entrainment process was employed to reproduce an experimental investigation on the impact of a spilling wave against a circular cylinder. The exerted in-line force was computed with and without the inclusion of dispersed bubbles. Results showed that the magnitude of the computed force was affected when the entrainment of bubbles was simulated.
Experimental Verification of ABS Concrete Design Methodology Applied to the Design of the First Commercial Scale Floating Offshore Wind Turbine in the United States
Authors: Dwyer Mark G. , Viselli Anthony M. , Dagher Habib J. , Goupee Andrew J.
Published: October 2017

The abundance of consistent high strength winds off the world’s coastlines and the close proximity to dense population centers has led to development of innovative marine structures to support wind turbines to capture this energy resource. Off the US coast, 60% of the offshore wind lies in deep water (greater than 60m) where the development of Floating Offshore Wind Turbine (FOWT) hull technology will likely be required in lieu of fixed bottom technology such as jacket structures. The United States National Renewable Energy Laboratory (NREL) and the offshore wind community commonly refer to 60m as the transition point between fixed bottom structures and floating structures due to economic reasons. Floating wind turbines deployed in the harsh offshore marine environment require the use of materials that are cost-effective, corrosion resistant, require little maintenance and are highly durable. This has led the University of Maine to develop a concrete hull technology called VolturnUS for full-scale 6MW FOWTs. In this work, experimental testing was conducted to verify the performance of the concrete under operational, serviceability, and extreme loading conditions as required by the American Bureau of Shipping Guide for Building and Classing Floating Offshore Wind Turbines. The testing included structural testing sub-components of the hull and served as experimental verification of American Bureau of Shipping (ABS) concrete design methodology which is currently approved and being used to design the first commercial scale FOWTs in the United States. Two 6MW wind turbines supported on VolturnUS concrete hulls will be used for the New England Aqua Ventus I project. The project is planned to be deployed and connected to the grid by 2019 in the Northeast U.S. and is funded by the US Department of Energy.
Low Cycle Fatigue of Subsea Mechanically Lined Pipeline With Liner Imperfections
Authors: Pépin Aurélien , Tkaczyk Tomasz , O’Dowd Noel , Nikbin Kamran
Published: October 2017

There is an ever-increasing demand for subsea transport of corrosive constituents which requires the use of corrosion resistant pipelines. This has generated interest in mechanically lined pipe (MLP) which consists of carbon steel pipe lined with a thin layer of corrosion resistant alloy (CRA), typically stainless steel. The CRA liner is adhered to the backing pipe by means of an interference fit.

MLPs have been traditionally installed subsea using low strain methods such as towing, S-lay or J-lay. More recently, the efficient reel-lay method, typically used for pipelines up to 18” (457.2 mm) in diameter, has also been considered. To prevent damage to the MLP during high strain bending (i.e. wrinkling of CRA the liner) and thus allow reel-lay installation, TechnipFMC has qualified reeling of MLPs at ambient and elevated pressures. The ambient reeling approach, where the liner thickness is increased to prevent wrinkling during reeling, is appropriate for smaller diameter MLPs. For larger pipelines, it is generally more cost-effective to pressurise the MLP during reeling.

Concerns have been expressed that liner imperfections such as small dents or wrinkles, introduced during manufacturing, installation or service, may compromise the integrity of the MLP subjected to high in-service cyclic loading. Therefore, this study was undertaken to examine the criticality of such flaws and determine the low cycle fatigue endurance of reeled MLPs with imperfections. First, a numerical study was undertaken to estimate in-service stress/strain ranges in the MLPs with liner flaws. Subsequently, small scale tests were carried out to quantify the fatigue performance of such MLPs. The obtained results confirmed that there is a negligible risk of failure of MLP flowlines due to crack initiation at liner imperfections and subsequent breach of the CRA layer, even for pipelines subjected to very severe inservice cyclic loading.
Numerical Investigation of Parametric Rolling of a Container Ship in Regular and Irregular Waves
Authors: Rajendran Suresh , Guedes Soares C.
Published: October 2017

Parametric rolling of a post-Panamax C11 class containership in regular and irregular waves is numerically investigated using body nonlinear time domain methods based on strip theory. The Froude-Krylov and the hydrostatic forces are calculated for the exact wetted surface area under the undisturbed incident wave profile. Two kinds of formulations are used for calculation of the radiation forces. The first one employs a linear radiation force in which the frequency dependent hydrodynamic coefficients are calculated for mean position of the sections at mean water level. The second formulation calculates the hydrodynamic coefficients for the exact submerged depth of ship sections under the undisturbed incident wave profile, and hence called as body nonlinear radiation force. The numerical results from the aforementioned formulations are compared with each other, and also with experimental results obtained from a wave tank in both regular and irregular waves. For all the cases in regular waves, the vulnerability to parametric rolling is clearly identified by the numerical models, even though a few discrepancies are observed in the estimation of the severity (maximum roll angle) of the problem. In this paper, the effects of the linear and body nonlinear radiation forces on the numerical calculation of parametric rolling of a container ship and the ability of the numerical methods to identify parametric rolling are investigated.
Dynamic Forces and Limiting Sea States for Installation of GRP Protection Covers
Authors: Solaas Frøydis , Sandvik Peter Christian , Pâkozdi Csaba , Kendon Timothy , Larsen Kjell , Myhre Erling
Published: October 2017

This paper describes a study aimed at finding and demonstrating a feasible method to reduce the uncertainties in calculation of dynamic forces and limiting sea states for installation of protection covers produced from glass fiber reinforced polyester (GRP). Uncertainties arise in the choice of hydrodynamic coefficients and the applied analysis method e.g. the Simplified Method, as suggested in DNV-OS-H206, versus time-domain simulations. The maximum limiting sea state for water entry and lowering through the splash zone has been assessed stepwise by use of alternative methods. Firstly, the hydrodynamic force coefficients for a fully submerged, selected GRP cover were estimated manually, by use of simplified data in DNVGL-“Recommended practice for modelling and analysis of marine operations”, DNVGL-RP-H103. The estimated hydrodynamic added mass was compared with the potential theory solution obtained by use of WAMIT. WAMIT calculations are also performed to obtain added mass and potential damping for the cover with different draughts at the selected installation angle. Viscous damping and added mass will be dependent on amplitude of oscillation and is studied by CFD simulations. A fully submerged cover is oscillated harmonically with different amplitudes at a selected period. The obtained added mass and damping coefficients were used in a numerical model including installation ship, lifting gear and GRP cover, in the non-linear time domain simulation program SIMO. The lowering through the splash zone were finally performed in some selected wave conditions to illustrate how a realistic limiting sea-state for the lowering through the splash zone may be estimated.
Unstable Well Behaviour in Gas Well Liquid Loading
Authors: Belfroid S. P. C. , van Wijhe A.
Published: October 2017

Liquid loading is the mechanism that is associated with increased liquid hold-up and liquid back flow at lower gas flow rates in gas production wells. In laboratory, most liquid loading experiments are performed at fixed gas and liquid rates (mass flow controlled). In the field, the well behavior is a coupled well-reservoir system in which the reservoir results in a pressure or mass flow controlled inflow, depending on the reservoir characteristics. In this paper results are presented which have been performed with a pressure controlled vessel attached to a vertical pipe. The pressure drop between the vessel was varied to represent reservoir characteristics from tight to prolific. The goal of the experiments was to evaluate the relation and the time ‘trajectory’ between the minimum in the pressure drop curve and the actual flooding point. From these experiments it was concluded that the stability is determined by the overall pressure drop curve. That is the pressure drop from vessel to separator and not the tubing pressure drop curve. This stability point can be at a higher or lower velocity than the actual loading/flooding point and therefore, loading is not the cause of the production decrease. That also means stable production is possible below the flooding point in slugging conditions. In future, the distinction between stable flow and loading/flooding must be made more strict.
Modelling of the Dynamic Behavior of the Power Transmission of an Automatic Small Scale Drilling Rig
Authors: Cayeux Eric , Skadsem Hans Joakim
Published: October 2017

The automatization of the drilling process opens the opportunity to faster reactions in case of unexpected drilling conditions, therefore reducing the risk that a drilling incident escalates to a serious situation. It also allows to push the drilling performance to be as close as possible to the limits of drillability as a function of the varying drilling conditions. But to achieve high level of drilling process automation, it is necessary to have access to accurate mathematical models of the complex physical system that is composed of the drilling rig, the drill-string, the drilling fluid and the borehole itself.

As the development of accurate heat transfer, mechanical and hydraulic models and their utilization in full scale drilling applications is a huge and complex task, it is tempting to recreate drilling automatization problems in a laboratory scale setup.

Because of sudden variations of the downhole drilling conditions, like when transitioning from soft to hard rock or when the bit is subject to large torque variations induced by interbedded rock layers, the boundary conditions at the bit change suddenly and require quick response from the automatic top-drive and hoisting system controllers. At a small laboratory scale, the necessary reaction times are of the order of milliseconds and therefore exclude any manual intervention. It is therefore crucial that the automatic control methods utilize precise mathematical models of the physical system to accurately estimate the limits by which the drilling process can be managed under safe conditions. For that reason, a general purpose mathematical model of small-scale drilling rigs has been developed.

First, the Rayleigh-Ritz method is used to determine the deflection of the drill-string and to estimate the side forces at the contact points along the drill-string and BHA (Bottom Hole Assembly). Then the dynamic response of the power transmission system is modelled for both variable frequency drive controlled tri-phase motors and for stepper motors, including friction effects at the contact points. Friction is modelled using Stribeck theory rather than the classical Coulomb laws of friction. Finally, the expected response of 3D accelerometers, that could be placed on the outside of a BHA component, is modelled to retrieve possible inclination variations and potential vibration modes such as torsional oscillations, forward or backward whirl.

The generality of the model is such that it can be used for many small-scale drilling rig designs.
Full Cycle Resource Evaluation of SMS Deposits Along the Arctic Mid Ocean Ridge
Authors: Ellefmo Steinar Løve , Ludvigsen Martin , Frimanslund Erik Kristian Thon
Published: October 2017

Several hydrothermal vent sites have been discovered along the portion of the Arctic Mid-Ocean Ridge (AMOR) inside the extended Norwegian continental shelf (NCS). Seafloor massive sulfide (SMS) deposits are associated with these hydrothermal vent sites. These deposits contain significant amounts of valuable metals, such as copper, zinc, gold, and silver. Loki’s Castle is one of the most promising sites along the AMOR, with two 20–30 m high and 100 m wide mound-shaped SMS deposits. It is located at a water depth of 2,400 m. A production system concept is proposed for a deep-sea mining operation at Loki’s Castle based on the Nautilus Minerals’ Solwara 1 project. The overall cost structure and design of the Nautilus’ concept is in this study regarded feasible in AMOR in spite of the difference between the operating environment for the two locations. As the only relevant operational experience is De Beers’ shallow-water diamond mining off the coast of South Africa and Namibia, most of the environmental criteria used are taken from offshore drilling. Based on the net operating time, and accounting for scheduled maintenance and waiting-on-weather time, an estimate for annual average production rate and an annual production volume are estimated. Significant downtime is expected in January and July.

Significant uncertainties are associated with early phases of projects. Probabilistic cost, grade and price estimates allow dealing quantitatively with uncertainties by giving input variables as probability distributions. Monte Carlo simulations are in this study run for different sets of variables, and the resulting key performance indicators are given as distributions.

This paper adapts and presents a methodology normally used to assess technological and economic feasibilities of oil and gas projects. The methodology is adapted to the assessment of deep-sea mining projects and is illustrated through the assessment of the case based on Loki’s Castle ore characteristics and technologies planned for the Solwara 1 project with a cost structure adjusted according to AMOR conditions. Costs for processing, refining, waste disposal and logistics after ore arrival at onshore port is not included. The ore uncertainties are huge and the resources are with the present deposit knowledge speculative. Therefore, this study do not attempt to define any reserves.
Nonlinear Dynamics of Multi-Segment Mooring Systems
Authors: Reddy Sandeep B. , Magee Allan Ross , Bai Wei
Published: October 2017

A general formulation applicable to multi-segment mooring systems is derived from first principles using the concept of lumped mass model and presented in this paper. The problem of seabed contact is addressed using an elastic-dissipative model of seabed. The contribution of seabed force along with the tension force is considered in creating global tangent stiffness matrix of the system. An implicit generalized-α method is used for time integration and it is modified for the current problem by developing an incremental iterative version of the method with corresponding predictor and corrector terms. An in house code named LM3D is developed based on the derived formulation. The code is verified with orcaflex results and also validated with experimental results. The main purpose of this paper is to showcase the reduction in tension observed in a simple branched mooring system when compared to a single line. Three configurations of branched system were considered and compared against a single line arrangement with same material properties. The dynamic analysis of this branched system was carried out with the developed in-house code.
A Time-Domain Method for Hydroelastic Analysis of Floating Bridges in Inhomogeneous Waves
Authors: Fu Shixiao , Wei Wei , Ou Shaowu , Moan Torgeir , Deng Shi , Lie Halvor
Published: October 2017

Based on the three dimensional potential theory and finite element method (FEM), this paper presented a method for time-domain hydroelastic analysis of a floating bridge in inhomogeneous waves. A floating bridge in both regular and irregular waves, is taken as a numerical example. This method is firstly validated by the comparisons of the results between frequency domain method and presented time domain method under regular wave condition. Then the hydroeleastic responses of the floating bridge in waves with spatially varying significant wave height/peak period are presented, with the purpose to illustrate the feasibility of the proposed method. The primary results at this stage indicate that the inhomogeneity of the waves might affect the structure dynamic responses of the floating bridge in waves.
pH-Sensor Under Consideration for Multi-Sensor-Chip in Downhole Drilling Fluid Monitoring
Authors: Kühne Jonathan , Güth Frederic , Strauß Heike , Joseph Yvonne , Árki Pál
Published: October 2017

Modern drill strings for the exploration of oil and gas are equipped with a variety of sensor carrying devices such as Measurement While Drilling (MWD), Logging While Drilling (LWD), and Formation Testing While Drilling (FTWD). These devices generate a large amount of downhole data, such as the orientation of the well, drilling parameters e.g. weight on bit and torque, and formation properties. Appropriate telemetry systems are included in the drill string to transfer relevant downhole data in real time to the surface. Other data is stored in memories downhole for subsequent evaluation. However, drilling fluid properties are still monitored at the surface and their behavior under borehole conditions is predicted with hydraulic models. Commercial solutions for a direct downhole measurement of various drilling fluid parameters are rare, though they would increase drilling process safety and the knowledge about the behavior of drilling fluids under real bottomhole conditions.

The pH has a significant influence on the properties of water-based muds and plays a role in the chemistry of oil-based muds as the water cut in the emulsion increases. Commercial pH-sensing devices, such as the glass electrode, and optical sensors are not appropriate for the pH measurement under bottomhole conditions. Fragility, the insufficient degree of miniaturization, the low temperature and pressure resistance due to the liquid reference electrolyte, and phenomena such as the alkaline error are certain drawbacks of glass electrodes. Often optical sensors often will not capture the whole pH scale and require the medium to be at least slightly transparent for light. The usage of pH-sensors based on EIS (electrolyte-isolator-semiconductor) structures is a possible application of chemical sensors for drilling fluid monitoring under in situ borehole conditions.

This paper presents results from a study on the behavior of an EIS structure as a pH sensitive electrode measured vs. a commercial Ag/AgCl reference electrode in comparison with a commercial glass electrode. EIS structures are capacitive pH sensors where the sensing layer is generally a metal oxide on a semiconductor substrate.

Measurements in basic drilling muds were conducted under constant temperature and atmospheric pressure while the drilling mud was steadily stirred. The mud was titrated from alkaline to acidic conditions with hydrochloric acid and the pH was measured after potential equilibration at the electrodes. The results show a general feasibility for the usage of the proposed sensor. There are still certain challenges to be overcome in the development of a robust and reliable pH-sensing device for complex fluids, such as drilling muds under high pressure/high temperature (HP/HT) conditions.
Summary and Conclusions of the Full Life-Cycle of the WindFloat FOWT Prototype Project
Authors: Roddier Dominique , Cermelli Christian , Aubault Alexia , Peiffer Antoine
Published: October 2017

The WindFloat prototype is a semisubmersible type foundation supporting a 2 MW, 3 bladed, horizontal axis Vestas V-80 turbine. The 8-year project is near its completion. After 3 years of planning, engineering and fabrication, the prototype was installed in 2011 in the northern Portugal Atlantic waters. Following 5 years of operations and electricity production, the unit was decommissioned in the summer of 2016. This paper retraces the prototype project going back to the early objectives, focusing on its 5-year performance and lessons learned. The overall assessment of the impact of the prototype on the incoming pre-commercial projects is discussed. Some emphasis is placed on both the decommissioning of the unit and the economics of the project, as these have not yet been published.
An Approach to Reduce the Amount of ILI Data in Fatigue Analysis of Pits in Pipelines
Authors: Larrosa Nicolas O. , Lopez-Crespo Pablo , Ainsworth Robert A.
Published: October 2017

This paper presents a screening methodology that is used to reduce the amount of data requiring detailed analysis from that obtained during in-line inspection (ILI). The methodology uses ILI outputs (dimensions of flaws, orientation and distance from starting point) to generate a visualisation of the pits within the pipeline, a ranking of pits in terms of sphericity (roundness) and depth, to evaluate pit density and generate the models for finite element analysis. The rendering tool allows a clearer view of defects within the pipelines and provides a simplified way to focus on critical pits. For a particular case of in-field data provided by BP, the number of pits in a 12-inch riser of 11 km length was reduced from 1750 obtained to 43, 15 or 4 requiring analysis, depending on the level of conservatism introduced by the analyst. The tool will allow Oil and Gas owners and operators to reduce the immense amount of data obtained during pigging to a much less time-consuming set for flaw assessment.
Investigation of EGR With EGB (Exhaust Gas Bypass) on Low Speed Marine Diesel Engine Performance and Emission Characteristics
Authors: Wang Zhanguang , Zhou Song , Feng Yongming , Zhu Yuanqing
Published: October 2017

In 2016, the International Maritime Organization (IMO) has enforced stricter nitrogen oxide (NOx) emission standards. Exhaust gas recirculation (EGR) technology is an effective way to achieve IMO Tier III standards for two-stroke marine diesel engines. This paper selected the 6S50ME-C8.2 diesel engine for the study, by making use of GT-POWER simulation software. In this paper, three different types of EGR were built to investigate the effects of EGR on engine performance and NOx emissions.

The results show that both the high pressure EGR system and the low pressure EGR system can reduce NOx emissions with the power drop and BSFC risen.

While in the high pressure EGR system combined with EGB, more NOx can be reduced with less power drop and BSFC risen. What is more, the running points of the compressor are still in the high efficient area and away the surge margin.

Based on the conclusions, the results obtained in this paper can offer reference for the turbocharged diesel engines with EGR system to reduce NOx emissions and improve engine performance.
The Effect of Stick Stiffness of Friction Models on the Bending Behavior in Non-Bonded Flexible Risers
Authors: Dai Tianjiao , Ye Naiquan , Sævik Svein
Published: October 2017

This paper investigates the effect of stick stiffness on the bending behavior in non-bonded flexible risers. The stick stiffness was normally implemented in the friction model for calculating the friction stress between layers in such structures. As the stick stiffness may be too small to achieve the plane-surfaces-remain-plane assumption under low contact pressure in some friction models [1], a new friction model was proposed for maintaining the constant stick stiffness in the present work. Less stick stiffness than that obtained by the plane-surfaces-remain-plane assumption was observed in test data. It was assumed that the stick stiffness reduction is caused by shear deformation of plastic layers. A numerical study on stick stiffness by including the shear deformation effect was carried out and verified against full scale tests with respect to the bending moment-curvature relationship.
Laboratory Experiments on Ultrasonic Logging Through Casing for Barrier Integrity Validation
Authors: Talberg Andreas Sørbrøden , Johansen Tonni Franke , Larsen Idar
Published: October 2017

Verification of annular barriers is essential for well integrity, with ultrasonic methods being central in well integrity testing for many decades. By doing ultrasonic pitch-catch measurements on a bench top laboratory setup developed to replicate an oil well casing, we were able to show that the beam width, −6dB, of the leaky Lamb wave propagating in the pipe widens only from 14 to 20.4 mm after 140mm of propagation in the pipe. This indicates that the excited Lamb wave has beam-like features, with litle spreading perpendicular to the propagation direction, hence, can be used to evaluate a limited area of the pipe. When introducing two pipes in the experimental setup, as an extension of a previously conducted simulation study by Viggen et al. [1], we could observe multiple Lamb wave packets being excited in the pipes. By adjusting the setup to replicate casing eccentricity, the effects of this could be observed in the measurements.
Effect of GMAW Heat Input on the Microstructure and Mechanical and Fatigue Behavior of Dissimilar Welds of Ultrahigh Strength Steel and Duplex Stainless Steel
Authors: Tasalloti Kashani Hamed , Dabiri Mohammad , Kah Paul , Martikainen Jukka
Published: October 2017

The effect of heat input on the microstructure and mechanical properties of dissimilar welds of direct-quenched ultrahigh strength steel (Optim 960 QC) and duplex stainless steel (UNS S32205) was studied. The effect of heat input on grain coarsening and the proportion of bainite-martensite on the ferritic side and ferrite-austenite on the duplex side was clearly evident. The hardness profile showed a trend of increasing hardness with lower heat input. Enhancement in tensile strength corresponded to lower heat input and increase in hardness. The elongation values and bend behavior were roughly the same for all the specimens; there was no clear link to the heat input. Moderate heat input gave optimum impact toughness in the weld and the ferritic HAZ. The fatigue performance of the specimens demonstrated the profound influence of geometrical effects. However, the effect of microstructural characteristics on fracture location was also observed.
Prof. Torgeir Moan and the Record Breaking Fjord Crossings in Norway
Authors: Skorpa Lidvard , Jakobsen Bernt , Østlid Håvard
Published: October 2017

Technology and competence from offshore structures, which were developed to serve in the harsh environment of the North Sea, have played a major role in developing technology for extreme fjord crossings in Norway. The Høgsfjord Project, and later the E39 Fjord Crossings Project, have taken advantage of the existing competence and experience from offshore structures. To a great extent, it has been a question of adapting offshore technology and combining it with advanced bridge technology to new types of structures. These new bridges are in many respects very different from offshore structures, mainly due to their length, slenderness, long resonance periods and complex dynamic behavior.

Professor Torgeir Moan has been heavily involved in the technology development for the fjord crossings. First, in the Høgsfjord submerged floating tunnel project, and now in the Fjord Crossings project with the bold aim of making the E39 Coastal Highway along the west-coast of Norway free of ferries. He has always showed genuine interest in the challenges, and have always been willing to help identifying and solving the problems. His contribution has been vital to the outcome of the work.
Fatigue Assessment of Drill Pipes
Authors: Haagensen P. J. , Grøttum T. I.
Published: October 2017

Fatigue failures during offshore drilling operations is still a very costly problem. The fatigue behavior of drill pipes is reviewed, and typical failure modes are identified. The effects of drill string curvature during directional drilling on pipe body stress and on the fatigue life is examined. Effects on applied mean stress from drill string weight are discussed. Interaction effects of degradation mechanisms such as fatigue, wear and corrosion are evaluated. Experimental background data and statistical evaluation that form the basis for the current design practice issued by American Petroleum Institute (API) and other guidance in codes and standards is reviewed. Results from several recent testing programs performed under rotating bending of pipes with threaded connections, and tests involving the pipe body under resonance conditions are presented. The tests were made with pipe sizes from 2 7/8 in. to 5 7/8 in. in Grade S-135 pipes. The results are compared with published test data and design guidance such as API Recommended Practice G7 [1]. Recommendations are given for research and testing to improve reliability and the safe operation of drill strings.
Hydrodynamic Analysis of Multiple Floating Pontoons With Different Joint Gaps to Waves in Different Water Depth
Authors: Chen Xujun , Miao Yuji , Tang Xuefeng
Published: October 2017

The hydrodynamic analysis of a multiple pontoon-type floating bridge (FB) interacting with oblique waves in water of finite arbitrary depth can be performed, at least in principle, using a general-purpose radiation-diffraction code. The fluid is assumed to be inviscid, and the flow can be considered as incompressible and irrotational, and the velocity potentials are calculated by boundary element method. To study the influences of the water depth and the gap between bodies on the hydrodynamic properties of the pontoons, RAOs (Response Amplitude Operators) of modes of each pontoon versus the wave frequencies are calculated and presented. The results show that the RAOs of pitch modes of different pontoons have differences in high frequency in heading waves, and those RAOs differences of heave of different pontoons in heading and oblique waves are small. Furthermore, all the others results nearly match into one. The influences of width of the gap between pontoons to RAOs are small, but the water depth has obvious influence on RAOs. In addition, the motions of FB are simulated and compared in different sea conditions which are represented by the JONSWAP spectrum. The results show that not only the peak wave periods but also the significant wave heights have obvious influences on the motions of the FB.
Acoustic reciprocity: An extension to spherical harmonics domain
Authors: Samarasinghe Prasanga , Abhayapala Thushara D. , Kellermann Walter
Published: October 2017

Acoustic reciprocity is a fundamental property of acoustic wavefields that is commonly used to simplify the measurement process of many practical applications. Traditionally, the reciprocity theorem is defined between a monopole point source and a point receiver. Intuitively, it must apply to more complex transducers than monopoles. In this paper, the authors formulate the acoustic reciprocity theory in the spherical harmonics domain for directional sources and directional receivers with higher order directivity patterns.