bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observed Wave Actions on Norwegian Semi-Submersible and TLP Decks
Authors: Kvitrud Arne , Løland Anders H. 
Published: September 2018

Waves have impacted decks on Norwegian semi-submersibles (semis) and TLPs several times. However, it did not get necessary attention before two accidents in 2015.
In 2015, a wave impact caused a fatality and four injured on the semi-submersible drilling rig COSLInnovator. The same year, a wave washed away gratings on Scarabeo 8, causing a man to fall 13.5m to the sea. When examining our records, we found 29 reported incidents related to waves in deck on 17 platforms from 2000–2017. 27 of the wave actions were mainly directed upward and the remaining two were mainly horizontal wave hits.
We describe each incident and the circumstances. We discuss common causes related to weather conditions and the physical appearance of the platforms. Further, we summarise design and operational precautions taken by the industry.
Qualification of Thermoplastic Composite Pipes
Authors: Wilkins Jonathan 
Published: September 2018

Magma Global has developed m-pipe®, a high performance pipe built from a thermoplastic matrix and carbon fibre, designed for use in subsea oil and gas applications to offer a high pressure and sour service capability. Managing the qualification of such a disruptive technology is a unique challenge. Magma must demonstrate reliability to our customers and to the regulators. There is little prior art that applies directly and so Magma is following the guiding principles in the recent DNVGL RP-F119 “Recommended practice for thermoplastic composite pipe” [1] together with the risk based approach in DNVGL-RP-A203 “Qualification of new technology” [2]. We discuss our approach to:
• Identify design and qualification standards.
• Develop tests to evaluate material behaviour at the coupon level in simulated oilfield environments.
• Develop an FEA based design tool to predict structural performance of pipes based on material properties tested on coupons.
• Correlate simulations to structural testing of pipes.
We hope the paper will be useful to anyone in the oil and gas community who is interested in developing composite materials and ensuring qualification for subsea applications.
Pure Bending Test on a Box Girder With Low Panel’s Slenderness
Authors: Gordo José Manuel , Guedes Soares Carlos 
Published: September 2018

The results of a four points bending test on a box girder are presented. The experiment is part of series of tests with similar configuration but different thickness, spacing between longitudinal stiffeners and span between frames. The present work refers to the stockiest plate box girder with a plate’s thickness of 4 mm and a span between frames of 800 mm. The experiment includes initial loading cycles allowing for residual stresses relief. It also includes a series of cycles close to collapse load allowing the analysis of linear characteristic at high levels of load.
The moment curvature relationship is established for a large range of curvatures. The ultimate bending moment of the box is evaluated and compared with the first yield moment and the plastic moment allowing the evaluation of the efficiency of the structure. The post buckling behavior and collapse mode are characterized. Comparison of the experiment with a progressive collapse method is made taking into consideration the effect of residual stresses on envelop of the moment curvature curve of the structure.
Drill Riser Fairing Hydrodynamic Assessment With 3-Dimensional Computational Fluid Dynamics Simulations
Authors: Lai Lawrence 
Published: September 2018

Fairings have historically been known to achieve in-line drag coefficients (Cdx) of approximately 0.60 across the Reynolds number (Re) range of 100,000 to 1,000,000, typical for the offshore environment [1]. The recent development of helically grooved drill riser buoyancy was shown to achieve Cdx values of 0.65 for this Re range [2], presenting a strong alternative to fairing products especially considering the additional installation, storage and maintenance requirements of fairings.
Therefore it is the purpose of this paper to investigate possible fairing designs capable of achieving even lower Cdx values where fairings can still be beneficial in further reducing drag loading. This paper proposes a non-parallel reduced chord horseshoe (RCH) fairing design and is analysed using computational fluid dynamics (CFD) in 3-d using the transient k-epsilon (Reynolds-averaged Navier-Stokes) turbulence model. The modelling approach is validated against tow tank test data of a previous teardrop-shaped (TD) fairing design which showed good agreement with published, peer-reviewed literature.
It was found CFD simulations with axially continuous fairings provide artificially low Cdx values due to the absence of fairing end-effects and gaps between fairing sections. In essence, an infinitely long and uninterrupted fairing in the riser axial dimension is not realistic. Incorporation of this discontinuity sees a significant increase in Cdx compared to the axially continuous fairing configuration. Although this is the case, it was found Cdx of approximately 0.48 or lower is achievable for the entire offshore Re range for the discontinuous fairing configuration (assuming a chord/diameter ratio of 2.0). Larger chord/diameter ratios would provide lower Cdx at the cost of a longer chord length which may impact fairing installation efficiency. Longer axial lengths would also achieve lower Cdx but with the risk of flutter instability.
This development in RCH fairing design sees a possible option for further fairing applicability to offshore drilling operations where lower drag is desirable beyond that offered by the helically grooved buoyancy.
Subsea Cable Stability on Rocky Seabeds: Comparison of Field Observations Against Conventional and Novel Design Methods
Authors: Griffiths Terry , Draper Scott , Cheng Liang , Tong Feifei , Fogliani Antonino , White David , Johnson Fraser , Coles Daniel , Ingham Stephen , Lourie Caroline 
Published: September 2018

As offshore renewable energy projects progress from concept demonstration to commercial-scale developments there is a need for improved approaches beyond conventional cable engineering design methods that have evolved from larger diameter pipelines for the oil and gas industry. New approaches are needed to capture the relevant physics for small diameter cables on rocky seabeds to reduce the costs and risks of power transmission and increase operational reliability.
This paper reports on subsea cables that MeyGen installed for Phase 1a of the Pentland Firth Inner Sound tidal stream energy project. These cables are located on rocky seabeds in an area where severe metocean conditions occur. ROV field observation of these cables shows them to be stable on the seabed with little or no movement occurring over almost all of the cable routes, despite conventional engineering methods predicting significant dynamic movement.
We cite recent research undertaken by the University of Western Australia (UWA) to more accurately assess the hydrodynamic forces and geotechnical interaction of cables on rocky seabeds. We quantify the conformity between the cables and the undulating rocky seabed, and the distributions of cable-seabed contact and spanning via simulations of the centimetric-scale seabed bathymetry. This analysis leads to calculated profiles of lift, drag and seabed friction along the cable, which show that all of these load and reaction components are modelled in an over-conservative way by conventional pipeline engineering techniques. Overall, our analysis highlights that current cable stability design can be unnecessarily conservative on rocky seabeds. Our work foreshadows a new design approach that offers more efficient cable design to reduce project capex and enhance through-life integrity management.
A Comparative Study of Fatigue Damage Assessment Methods to a Rigid Planar Jumper
Authors: Igeh Laila Aarstad , Liu Zhenhui , Wu Jie , Ong Muk Chen 
Published: September 2018

A rigid jumper is an important part of the subsea production system, it may experience significant vortex induced vibrations (VIV) if subjected to current. It has normally non-straight geometry shape in three-dimensional space. Consequently, the response of a rigid jumper under VIV is much more complicated compared to straight pipeline structures. Currently, there are very limited studies and design guidelines including methods on how to assess the fatigue damage of rigid jumpers under VIV. The methodology used for straight pipelines is often applied by ignoring the non-straight geometry characteristics and the multi-axial stress states (coexisting of flexural and torsional stress). However, both experimental and numerical results show that the torsional stress does exist besides the flexural stress for rigid jumpers under VIV. On the other side, the response of the rigid jumper under VIV is also challenging. The objective of this study is to do a fatigue assessment practice based on state-of-the-art calculation methods to a rigid jumper on model scale. The VIV response is inherited from experimental tests and numerical calculations by either force or response model methods. The influence of torsional stress on fatigue assessment is demonstrated. Two approaches have been investigated. In the first method, the flexural and torsional stresses are evaluated separately. The second method uses the 1st principle stress to calculate the fatigue damage, thus the flexural and torsional stresses are evaluated together.
It is shown that the use of the 1st principle stress gives higher fatigue damage if the torsional stress contribution is significant. Further, the principle stress method is also less time-consuming on processing the results. Detailed discussions based on results have been performed, which could be also applied to general real scale rigid jumpers.
Validation of Seismic Streamer Simulator and Sea Current Estimator Using Full Scale Data
Authors: Grindheim Jan Vidar , Revhaug Inge , Welker Ken , Solheim Peder , Pedersen Egil 
Published: September 2018

Survey optimization and cost reductions are ongoing challenges for the marine seismic petroleum exploration industry. The present research intends to improve seismic streamer steering as well as to reduce time on line-changes, where the streamer spread is turned 180 degrees. Sea current estimation and prediction of future streamer state are important aspects of improved streamer steering, which will increase survey efficiency and quality.
A seismic streamer simulator has been validated against full scale proprietary data from two seismic survey line-changes. The streamer spread has 12 cables of slightly more than 4 km length each, with 13 control birds for each streamer. Interpolated Acoustic Doppler Current Profiler (ADCP) measured sea current is introduced at the streamer nodes. Two streamer tension cells are installed at each streamer, giving validation of simulated tension.
Secondly, a sea current estimation algorithm has been validated against the interpolated ADCP current data for the two line-changes.
Mooring of Semi Submersibles in Extreme Sea States: Simplified Models for Wave Drift Forces and Low Frequency Damping
Authors: Larsen Kjell , Vigesdal Tjerand , Bjørkli Rune , Dalane Oddgeir 
Published: September 2018

This paper presents results from extensive small-scale model testing of three semi submersibles together with an overview of damping contributions of low frequency motions. The objectives of the model tests were to verify empirical correction formulas for viscous wave drift forces and to recommend and validate theoretical low frequency damping models. The main parameters of the semis such as displacement, number of columns and diameter of columns were intentionally varied in order to assess the effects on total wave drift forces and corresponding damping. The results show that viscous effects significantly increase the total wave drift forces in extreme sea states. The presence of current increases the effect. As expected, the viscous contribution to wave drift is especially important for semis with slender columns. A revised empirical correction formula for wave drift forces is proposed based on model test results.
An overview of the different low frequency damping effects is given. Damping from viscous forces on the hull and damping from the mooring system are the most important sources of damping for the moored semis. A simplified model to calculate mooring system damping is proposed. For accurate prediction of low frequency motions of moored semi submersibles in extreme sea states, a damping level in the range 40–70% of critical damping should be applied for surge and sway when the empirical correction formulas for wave drift forces are applied.
A New Method in Identifying Critical Void Volume Fraction of GTN Model for NVA Mild Steel in Ship Collision and Grounding Scenario
Authors: Song Zijie , Hu Zhiqiang 
Published: September 2018

The NVA mild steel is a commonly used material in shipbuilding, which possesses good ductility character. However, the description of ductile fracture process for NVA steel in numerical simulation is still a challenging task. A new method to predict the critical void volume fraction fc of Gurson-Tvergaard-Needleman (GTN) model is introduced in this paper.
GTN-model is one of the well-known micromechanical models for ductile fracture. The traditional plasticity theory assumes that the plastic volume is incompressible and that the yield of the material is independent of the hydrostatic stress, whereas the yield surface of the GTN-model takes the effect of the macroscopic hydrostatic stress into account. The yield surface is reduced with the increase of the void volume fraction, which can reflect the deterioration characteristics of the material with development of damage during the deformation process. Therefore, GTN-model is a promising mathematical model for describing the ductile fracture process of the ship structures during accidental scenarios of collision and grounding.
The traditional way to determine fc of GTN-model is using the inverse method directly, which has a high degree of uncertainty. A new method based on Hill, and Bressan & Williams’s assumptions proposed in this paper solve this problem effectively. Besides, the combined of Voce and Swift constitutive model is used to describe the mechanical property of the NVA material.
Furthermore, numerical simulations were also conducted with code LS_DYNA by developing the user-defined subroutine. It is found that the model can predict the structural damage quite accurately, which proves its feasibility of being applied in the research of structural responses in ship collision and grounding accidents.
Validation of Applicability of Low Frequency Motion Analysis Theory Using Observation Data of Floating Offshore Substation
Authors: Yoshimoto Haruki , Yoshida Hisafumi , Kamizawa Ken 
Published: September 2018

In recent years, the social demands for the introduction of renewable energy are increasing, demonstration projects of floating offshore wind power generation are being implemented and planned around the world. In Japan, a demonstration project named Fukushima FORWARD (Fukushima Floating Offshore Wind Farm Demonstration Project) has been conducted since 2011. Fukushima FORWARD is carried out by the Ministry of Economy, Trade and Industry. The project is the world’s first floating offshore windfarm with a total capacity of 14 MW, including three floating offshore wind facilities and one floating offshore substation. In Fukushima FORWARD, Japan Marine United Corporation is in charge of floater part EPCI (Engineering, Procurement, Construction and Installation) of one floating offshore wind facility and one floating offshore substation.
This floating offshore substation is installed in order to observe meteorological and oceanographic data and motion data as well as boosting the generated electric power. Since the installation in 2013 it continues to record various kinds of continuous data. The substation is an advanced spar type floater moored by four spread catenary mooring lines.
In the design of the mooring system for offshore structure, the motion of the structure under environmental external force is very important. The motion of the moored floating structure is divided into wave frequency motion, which is a motion of a relatively short period, and low frequency motion caused by mooring restoring force and variable external force, both of which are important elements in the design. Among them, wave frequency motion is known to be accurately estimated by potential theory as a result of research on various types of structures. On the other hand, in addition to the existence of various calculation methods including time domain analysis, its statistical characteristic and applicability are entirely depending on the target structure. Also, observation data of low frequency motion have been very few.
In this paper, long-term data observed at the floating offshore substation in Fukushima FORWARD was analyzed with focusing on low frequency motion and its statistical properties were clarified. Furthermore, we analyzed the low frequency wave force spectrum and motion by conventional low frequency motion theory using the wave drifting force calculated by the potential theory. And, we compared the calculated value with the analysis result of the observation data and validated the applicability of the simplified low frequency motion theory.
Similarity Analysis for Downscaling a Full Size Drill String to a Laboratory Scale Test Drilling Rig
Authors: Ambrus Adrian , Skadsem Hans Joakim , Mihai Rodica G. 
Published: September 2018

The drill string used in drilling oil and gas wells is a long and slender structure that is confined by the wellbore wall and subject to significant axial, lateral and torsional vibrations while drilling. Detection and mitigation of drill string vibrations are especially important, as vibrations can be hard to detect at the surface, yet cause significant damage to the drill bit, downhole tools and the formation being drilled.
Study of the drilling process by downscaling to laboratory conditions is an attractive prospect as it is a cost-efficient alternative to dedicated large-scale testing and it can be instrumented to provide vibration measurements from different locations along the string. However, the extreme geometrical length scales, the complex wellbore trajectories and the large mechanical strains on the drill string lead to challenges when attempting to downscale the drilling process to manageable laboratory conditions.
Downscaling based on similarity analysis provides consistent scaling laws for predicting large-scale dynamics based on observations from the downscaled test drilling rig. We perform a similarity analysis for an example full scale drill string that illustrates these challenges in terms of similarity criteria for an equivalent laboratory model of the drill string. We focus particularly on the geometric and mechanical properties of the drill string and consequences of downscaling on the time scale and the forces in the string. We illustrate the downscaling criteria through numerical simulations by solving the governing equations of motion at different scales, and provide recommendations for downscaling based on widely available material types.
Autonomous Inflow Control Device Pilot Application for Extra Heavy Oil Field
Authors: Abdel Rafea Mahmoud , Criado Cristhian 
Published: September 2018

Autonomous Inflow Control Device (AICD) completion was successfully designed and applied in a horizontal well drilled in a deep reservoir in an extra heavy oil field located in South America where the average total depth of the targeted reservoir is around ten thousands feet and the in-situ viscosity is 600 cps while API Gravity is ranged between 8.5–9.5.
Due to geological and petro-physical features in this area which turns into permeability variations and thick transition zone across the reservoir, a horizontal well of 2500 feet length was drilled and completed with a standalone screen along with Autonomous Inflow Control Device (AICD) to avoid sand production and delay water production. The initial design for the AICD considered the variation of permeability, rock quality, pressure differential across the horizontal length including the operational factors. Accordingly, multiple scenarios using reservoir simulation built-in model (Petrel-RE) and Netool for ICD selection, design and placement where the geological properties of the model were updated based on the run NMR and Caliper logs while geo-steering the well. Also, a fine grid sector model was generated to assess optimum well completion design.
The AICD completion was successfully deployed and resulted in extending the well life by delaying water production and it is expected to get its ultimate benefit whenever starting the implementation of a water flood project near that producer well.
Algorithm for Auto-Piloting Efficient Seismic Line-Change Turning Maneuvers
Authors: Grindheim Jan Vidar , Revhaug Inge , Welker Ken , Solheim Peder , Pedersen Egil 
Published: September 2018

Seismic surveys for petroleum exploration utilizing towed streamers are typically performed line by line. Between the lines, a 180° turn of the complete towed gear is necessary. This operation is time consuming and thus expensive. There is evidence in the literature that the turn maneuver can be made more efficient by taking advantage of favorable sea currents [1].
In the present study, an autopilot algorithm is developed for performing efficient line-change maneuvers, taking into account sea current, if present. The algorithm controls the vessel path and speed during the turn, as well as the streamer bird forces. The algorithm has been developed and validated utilizing a proprietary towed seismic streamer simulator, employing realistic seismic streamer spreads.
Simulation results for ranges of sea current speeds and bearings are presented for two different seismic spread configurations. Turning times are compared to estimated traditional turning time ranges.
Steady-State Cuttings Transport Simulation in Horizontal Borehole Annulus
Authors: Ignatenko Yaroslav , Bocharov Oleg , Gavrilov Andrey , May Roland 
Published: September 2018

The paper presents the results of modeling the steady-state flow of drilling fluid with cuttings in an annulus for the flow regimes typical for horizontal drilling. The studied parameters include effects like fluid rheology, drillstring rotation and eccentricity on flow regime, pressure drop and cuttings bed.
It has been demonstrated that increasing the drilling fluid’s effective viscosity increases the pressure drop, but it decreases the cuttings bed area, while drillstring rotation significantly changes the flow structure, improving cuttings transport and reducing the pressure drop. The considered flow structure can change abruptly due to changed drill string positioning and rheological fluid properties. Such structural changes are followed by abrupt changes in the pressure drop and cuttings bed area.