bluuebunny/crossref_metadata_2025 huggingface dataset:
Introducing Single Deck Topside Concept for Large New-Build FPSOs in West Africa
Authors: Kim S. E. , Kim S. H. , Chung B. Y. , Lee I. H. , Jung J. J.
Published: April 2017

The era of the low oil price makes all key players to establish the distinct business and technical strategies from the past successful models of offshore plant for better construction and operation. This paper describes design features of a single deck topside and wide beam hull concept for large new-build FPSOs in West Africa. The single deck topside is a common concept in the platform of small production capacity, while it is not applied to large new-build FPSOs. Generally, multiple deck topside has been introduced to large FPSOs to carry a lot more equipment within allowed footprint area. But, it has caused heavy structural reinforcement and complicated layout in topside. To overcome this shortcoming in Large FPSOs, our approach increases the hull deck area, mainly by the breadth more than conventional vessel. Equipment is grouped by the functional similarities and arranged on larger main deck. Other fitting and less heavy equipment may be located on the self-supporting structure. The major piping route, valve location and topside structure are also verified. Combination with mega-block modules could enhance the benefits of this concept, especially in saving the execution time and obtaining the design flexibility. Further, it creates more value of the maintainability by open overhead access to the main equipment, not compromising the safety. Initial hull sizing is carried out in terms of optimizing weight and motion characteristics. Several barriers are reviewed for realizing the single deck topside and wide beam hull, based on the previous experience. Finally, the benefit of this concept is validated by the 3D modeling. In this paper, the main findings and further discussion points from the study are addressed.
Long-Term Abrasion Test for Seabed Mining Hose Liners
Authors: Neale Peter , Nagy Tibor , Grepaly Istvan , Tóth Péter , Kristóf Gergely , Csobán Attila
Published: April 2017

The results of a long term abrasion test on 10" hoses were compared to flow simulation based abrasion calculations. An impact angle dependent small scale abrasion test was carried out on the rubber liner material to establish input data for abrasion simulation. The simulation proved to be very sensitive to the dependence of the impact angle on the abrasion rate, particularly at low impact angles. Three different lining materials were applied in the full scale test: rubber, a proprietary plastic liner and rubber with built in hard steel rings using a purpose built machine. The abrasion rate increased in the following order: armored liner, rubber and plastic, although the plastic had better Schopper abrasion than rubber.
Residual Strength Pushover Analysis: Enhanced Assessment of Seismic Platform Performance
Authors: Litton Richard , Ku Albert , Chen Jiun-Yih , Fraser Ramsay , Beck Richard
Published: April 2017

For abnormal (ALE) and reliability (RLE) level earthquake events (return periods of 2,500-10,000 years) used in the design or assessment process, there is a need to establish the acceptance of the structure's ability to survive the event. The present industry practice of subjecting a platform to nonlinear dynamic simulation of several severe events relies on significant and somewhat subjective judgments by the engineer in the determination of platform survival. This paper presents a method for quantifying the resulting damaged state, leading to a more explicit and reliable determination of platform robustness.

Residual Strength Pushover Analysis compares the ultimate strength of the undamaged or pre-earthquake condition of the structure to the residual strength of the structure after the severe earthquake using both pseudo-static pushover analyses and nonlinear dynamic time history analyses. The method requires nonlinear structural analysis software capable of capturing the damage state of the structure from the time domain earthquake simulation in a pseudo-static pushover analysis after the earthquake.

The research work presented in this paper shows a clear distinction between inefficient seismic framing systems such as K- and Diamond-braced systems in contrast to the robust, ductile systems utilizing X-bracing schemes.

Two separate case studies are presented in this paper to demonstrate the methodology and provide a recommendation for the acceptance criteria. One study uses a representative structure fitted with four different framing systems (K, Diamond, X without perimeter horizontals and X with perimeter horizontals) and the other uses an existing structure modified to improve seismic performance.
Combining the Most Efficient Active Heating Technology with Subsea Electrical Distribution to Develop Remote Resources
Authors: Verdeil Julien , Giraudbit Sonia , Silcock Donald , Cherkaoui Saad
Published: April 2017

Active heating technologies are for the moment based on topsides power distribution, limiting by default, the length of the flowline that can be heated. It is proposed to extend the range of active heating technologies by utilizing a field architecture that enables production for very long tie-backs by combining subsea electrical power distribution with the most efficient active heating technology the "Electrically Heat Traced Flowline" (EHTF) technology.

The paper will present typical field architectures that require such combinations of subsea electrical power distribution and efficient active heating technology, typically brown fields with remote tie-backs that could not be developed with available technologies.

EHTF Technology is based on a field proven high performance thermally insulated pipe-in-pipe, limiting the heat loss. Multiple high voltage wires, connected as three phase circuits, laid under the insulation along the entire length of the fluid carrier pipe, are used to provide heating. The heating wires extend typically 20km each side of a small in-line structure allowing safe penetrations into the pipe-in- pipe annulus. This small structure is powered on by a power cable, laid alongside the flowline, via a subsea electrical power distribution unit, which can be combined with a subsea transformer, to distribute the power to the multiple heating circuits within the annulus.

Exceptional thermal efficiency of the insulation system generates lower heating power requirements, meaning that subsea distribution systems can be designed with reliable and off the shelf components, easily retrievable and maintained with low operational expenditures.

Multiple circuits in the cross-section offer a greater operational flexibility and improved reliability of the system. Different power outputs can be provided from simple switching control depending on the heating requirement.

Combining an efficient, reliable and flexible active heating technology with a simple and robust subsea power distribution allows development of remote fields that can be tied-back to existing facilities, virtually without limitation in length.
On-Bottom Stability Analysis of Submarine Pipelines, Umbilicals and Cables Using 3D Dynamic Modelling
Authors: Youssef Bassem , O'Brien Dermot
Published: April 2017

Submarine pipelines and umbilicals are essential elements of many offshore hydrocarbon developments. In general, the most economical approach is to lay the pipelines and umbilicals directly on the seafloor with adequate self-weight to avoid any requirement to perform secondary stabilisation work such as trenching. A fundamental design requirement for this scenario is to ensure adequate pipeline stability under extreme environmental loading conditions, as excessive lateral displacements may result in pipeline or umbilical damage.

The commonly used and widely accepted recommended practice DNV-RP-F109 (Ref. 3) provides three design approaches with increasing levels of complexity to perform on-bottom stability design. These three design approaches are: Absolute Lateral Static Stability, Generalised Lateral Stability and Dynamic Lateral Stability Analysis. The first method is based on two dimensional (2D) force balance equilibrium equations while the second method is based on extensive dynamic modelling results of 2D pipeline models. These first two methods are intended to provide conservative on-bottom stability designs for rigid pipelines. The third method involves detailed finite element modelling of the pipeline under a time domain hydrodynamic loading.

This paper highlights the DNV-RP-F109 recommended practice limitations with respect to the on-bottom stability design of flexible pipelines, umbilicals and cables. The paper presents a dynamic simulation methodology, in accordance with the recommended practice DNV-RP-F109, for on-bottom stability design of rigid pipelines, flexible pipelines, umbilicals and cables, together with specific sensitivity analyses and comparisons with the Absolute Stability method.

The dynamic modelling results and comparisons presented in this paper highlight some limitations of the Absolute and Generalised methods for flexible pipelines, umbilicals and cables and illustrate the benefits of using the three dimensional (3D) dynamic stability analyses. The results of the sensitivity analyses clearly identify important parameters for the dynamic simulation, such as the hydrodynamic load correction due to the pipeline movements, the pipeline axial stiffness and the seabed passive soil resistance, that significantly affect the on-bottom stability behaviour. Refining the identified parameters input values will lead to more accurate and cost effective on-bottom stability design.
Design of an Energy Storage System ACAES Applied to Marine Renewable Energy: Study Case Based on Energy Integration Approach
Authors: Chassé C. , Lemois F. , Chilloux D. , Langeard O.
Published: April 2017

Marine energies (including wind turbine, tidal current and wave energy) are now recognized not only as high potential energy sources, but also as a significant and maturing energy market. Nevertheless, renewable marine energies are highly intermittent and so adequate energy storage systems are a main challenge for renewable marine energy development, to make it reliable and compatible with domestic and industrial power demand.

This paper focuses on the ACAES (Adiabatic Compressed Air Energy Storage) technology. It presents a study case of a large wind turbine farm (320MW capacity). After a state-of-art review on energy storage systems, the ACAES technology is selected as the most adequate solution for this case to store renewable energy, which means to store the entire produced power during low demand periods and to return all the stored energy during high demand periods. The operating principle of an ACAES system is that, using produced renewable energy, air is first compressed to be stored during low energy demand period. Storage is made through some natural cavity. Then the air is expanded during high energy demand period to return stored energy. A parallel heat transfer medium is used to make the system adiabatic.

An efficiency assessment is performed and key parameters are identified thanks to a heat and mass modeling and sensitivity studies. A suitable solution is selected and the storage system is sized, including process equipment (air compressors and turbines, motors and generators, pumps, water facilities as hot water storage and cold water storage, heat exchangers) and electrical systems. The required footprint is assessed by drawing a layout and a three-dimensional representation. The CAPEX of the selected ACAES system is estimated. Possible installation of this kind of storage system is assessed through a research on geological cavern and a review of available and possible air storages.

This work offers a comprehensive overview of a typical Adiabatic Compressed Air Storage installation, applying O&G plant design expertise to an emerging alternative energy, to make it reliable.
Feedback on the Design and Operation of the Skarv FPSO Mooring System
Authors: Naciri Mamoun , Heimsnes Tom Erik , Newport Andrew , Mée Romain le
Published: April 2017

The Skarv field, located 210 km offshore Norway, has been developed by BP using a turret moored FPSO, with first oil production achieved in December 2012. This paper presents the station keeping philosophy adopted for the FPSO, and gives an overview of the turret system design, and the challenges involved. In addition, based on four years of offshore operation, feedback on the behaviour of the mooring system is reported and compared with the design assumptions. The turret mooring system is located at 1/3 of ship length aft of the forward perpendicular, which reduces its passive weathervaning characteristics, leading to the provision of a heading control system to optimize topside ventilation, minimize turret loads and improve vessel motions. The harsh environment of the Skarv field, together with survivability considerations for a black ship conditions when power for the heading control is lost, result in mooring loads in excess of 5000 tons. These loads are significantly higher than loads imposed on previous FPSO turret mooring systems.

Operational experience from nearly four years will be compared to global performance as predicted during design stage through both analysis and model testing. Conclusions will be drawn about monitored global performance. Lessons learnt will be provided. Feedback from this frontier project will help the Industry tackle mooring system design in more and more challenging metocean conditions in the future.
The Qualification Methodology Behind an Integrated Multizone Frac Pack and Intelligent Completion for the Lower Tertiary
Authors: Jannise Ricki , Joubran Jonathon , Gavin Bruce , Coffin Maxime , Techentien Bruce , Geoffroy Gary , Craik Steve , Perez Eddie
Published: April 2017

Currently, ultradeepwater single-trip multizone completions are commonly run (Techentien et al 2016). Looking forward, improvement and progress can be achieved by using run history, lessons learned, and best practices. In the Lower Tertiary of the Gulf of Mexico, multizone completions in which differential pressure ratings of 15,000 psi are necessary, all operational stages should be considered, including stimulation treatments and production depletion. To date, little information is published about specific downhole component design methods or standard qualification processes required by operators and/or service companies. The objective of this paper is to help educate the industry by presenting the approach of one service company to address the 15,000 psi Lower Tertiary challenge.

This paper discusses the innovative qualification processes of all subsystems, including the intelligent upper completion, interfacing intermediate completion, and the sandface lower completion. The proven success of the industry-standard 10,000-psi generation IV (Clarkson et al. 2008) multizone frac-pack system (Grigsby et al. 2016) provides an installation and operating standard that is used as a basis for a 15,000-psi pressure-rated multizone system. Operators were interviewed, internal discussions with all stakeholders were conducted, and thorough reviews of current and future regulatory standards were completed to develop this methodology. This paper presents the results of these discussions and reviews the downhole components using a detailed qualification process. It also discusses the test procedures for full system validation to satisfy operator and regulatory requirements. The result is a reliable 15,000-psi differential, single-trip multizone system that incorporates an intelligent completion string for interventionless zonal isolation, control, and monitoring over the life of the well.
Cost Effective Solutions: Less is More
Authors: Agussol L. , Lavagna Ph.
Published: April 2017

In a >100 USD/bbl market, the project economics are optimized by different parameters than in a market below 50 USD/bbl. In high oil price context, the focus is on maximizing the revenue (i.e. production), whereas in low oil price context, the focus on costs is more important.

In today low oil price era, a new paradigm to optimize the project economics is << Less is More>>:

Less equipment/complexity can also be More safety and more Reliability – as less equipment lowers the probability of equipment failure, also reducing both CAPEX and maintenance costs

Less CAPEX/OPEX should enable More projects to become economically viable.

Going to the essence of simple and robust systems enables solutions for the low oil price era. Indeed, while the HSSE commitment is not negotiable, the extra costs related to systems required for maximizing the production uptime are to be challenged to adapt the projects to the new market conditions. Using the example of mooring systems, a functionality review is performed so that the functional specification can be optimized for today's new set of project constraints. This applies along the EPCI chain:

Engineering: where relevant experience (industry standards and field proven solutions) can be used to avoid re-calculating everything to the highest degree.

Procurement where functional specification in place of – often over demanding - client specifications enables more standardization and thereby significant savings on price, schedule and sparing philosophy.

Construction where the clients can focus on ensuring/monitoring the HSSE and QA/QC performance of the project by choosing an ‘hands off’ approach on the execution part which enables the full benefit of using a seasoned contractor.

Installation – especially for Turret & Mooring systems – the installation aspects needs to be integrated from the beginning (Engineering). The most cost efficient way for a safe installation is to have the installation scope integrated in the mooring system contract (i.e. EPCI instead of EPC).

All these simple principles (simplification, standardization, streamlining of the work, lean management) have to be implemented to enable project economic viability in today's market. This Less is More approach has been used on recent tenders and has allowed significant cost savings and schedule reduction leading to further cost reduction.
Effect of Hydrodynamic Parameters on the Wax Mass Density: Scale Up From Laboratory Flow Loop to Crude Production Pipelines
Authors: Agarwal J. , Ravichandran S. , Daraboina N. , Sarica C.
Published: April 2017

The oil and gas production pipelines typically operate at high Reynolds number and low wall shear stress conditions. However, the current wax deposition prediction models were developed based on the laboratory flow loop experimental data obtained at high shear stress and low Reynolds number. It is required to have reliable experimental data, which closely resembles the field conditions to validate the existing models or fine tune the effect of scale up parameters with available laboratory data. Hydrodynamic parameters such as Reynolds number and shear stress would incorporate the effects of diameter, flow rate and viscosity collectively, thus enabling a comprehensive approach for modeling the phenomenon. However, it is necessary to understand the individual effects of Reynolds number and shear stress as they are coupled.

In the present study, the effect of the hydrodynamic parameters is decoupled with specially designed flow loop experiments. The deposit thickness and wax content were measured, and the wax mass density (wax mass deposited per unit area) was calculated. Since the area of deposition is changing, the main variable analyzed in this study is the deposited wax mass density instead of the deposit thickness and wax content. From the results, it has been observed that the Reynolds number has a more dominant effect on the deposited wax mass density compared to shear stress. This behavior is observed for in house synthesized model oil and different crude oils at various experimental conditions. The results obtained in this study enhance our understanding on the deposition behavior at various hydrodynamic conditions and aids in scale up from the laboratory to field conditions. Moreover, in order to develop more accurate wax prediction models for operations particularly for waxy crude oil production lines, it is necessary to tune right scale up parameters for field applications.
Seismic Design of Subsea Pipeline Systems: Evaluation Study
Authors: Al-Showaiter A. , Kulkarni S. , Shi H. , Sun J. , Abdalla B.
Published: April 2017

When subsea pipelines and tie-in spools are supported directly on the ground, the differential ground movement due to seismic wave propagation may be neglected. This is because pipelines and spools have their centers of mass very close to the ground level. However, when the pipelines/spools are supported on, or connected to different structures (platform, subsea isolation skids, PLETs, etc.), the impact of the differential movements of these supports and structures on the pipeline and spools response should be considered.

The industry approach to the seismic design of a subsea pipeline system is that the system is designed for Extreme Level Earthquake (ELE) and is able to withstand Abnormal Level Earthquake (ALE) with some damage, but not loss of containment. The design of a pipeline system is iterative by nature. The pipeline loads on the subsea structure are input to the subsea structure design, while the subsea structure foundation resistance is an input to the pipeline integrity checks. Hence, an integrated model incorporating the pipeline, tie-in spools and subsea structures is the most comprehensive design method.

Pipeline systems are typically analyzed for seismic loadings by the modal response spectrum method, or time history analysis. The modal response spectrum method is a linear method and is not adequate when non-linearity should be considered (e.g. ALE). It is desirable that the designer should make every effort to ensure that the ALE is a confirmatory check, which should not lead to major adjustments in the design. To achieve this vision, the designer should use ductile material and the design should have sufficient flexibility; meaning that the system should be able to undergo large deformations without loss of containment. In essence, a time history method should be adopted. However, it is not often economical or a trivial task to perform such analysis in the early phases of the project definition (i.e. concept selection or pre-FEED) or even during the FEED phase.

Taking a case study, the application of different seismic analysis approaches to a pipeline system, including pipelines, tie-in spools, and subsea structures, is presented and evaluated. This paper also recommends the appropriate level of seismic analysis for different phases of project definition.
Modeling of a Full-Scale Horizontal Liquid-Liquid Separator under Conditions of Varying Flow Rate, Water Cut, and Viscosity with Experimental Validation
Authors: McCleney A. B. , Owston R. A. , Green S. T. , Viana F. , Nelson S. M.
Published: April 2017

Computational simulation of a full-scale, horizontal liquid-liquid gravity separator has been undertaken by Southwest Research Institute® (SwRI®) to model the batch separation of oil and water flow. Separator modeling using Computational Fluid Dynamics (CFD) represents a powerful and economical option for design, but caution must be used in the setup and interpretation of data. Many examples are available in literature of poor agreement between simulation results and experimental/field data. No clear consensus on valid modeling methodology currently exists. Results require interpretation before taking them at face value due to the complexity of the various submodels that can be utilized. This work offers an evaluation of multiphase flow modeling techniques, and provides a unique comparison with experimental data that covers a broad range of flow rates, water cuts, and viscosities.

The performance of a horizontal gravity separator with perforated baffles has been investigated using CFD. The simulations have been carried out using an Eulerian-Eulerian multiphase approach. These simulations were conducted using constant dispersed water droplet sizes in an oil-continuous phase. Separation efficiencies and water-cut percentages at several locations throughout the test separator were compared against experimental results for a wide range of inlet flow rates, water cuts, and oil viscosities. Computational results indicated that the horizontal liquid-liquid separator can be modeled within 10% accuracy of the local experimental separation efficiency values for the various test conditions. This effort demonstrates the capability of reliable modeling of multiphase flow fields inside of horizontal gravity separators, and offers an economical option for aiding in the design of separation equipment.
Comparison of Self Weight Penetration Prediction Methods for Large Diameter Monopiles in North Sea Soils
Authors: Shonberg A. , Anusic I. , Harte M. , Schupp J. , Meissl S. , Liingaard M. A.
Published: April 2017

A significant number of large diameter monopiles (>6 m diameter) have been installed as foundations for offshore wind turbine generators (WTG) across Northern European waters over the past decade, where the self-weight penetration (SWP) during the installation process was recorded. The prediction of the SWP for offshore foundations, such as piles and skirted foundations, is an important installation design task. The prediction of the SWP is subject to great uncertainty, resulting in a large range between lower and upper bound SWP predictions.

The methods available to predict the SWP range from simple empirical methods that derive the penetration resistance from cone penetration test (CPT) measurements using skirt and tip resistance coefficients to more advanced methods, based on bearing capacity theory requiring soil strength parameters as input. For the empirical methods, the prediction accuracy is directly dependent on the data used to establish suitable resistance coefficients. Investigating different soil conditions and foundation dimensions (scale effects), therefore, extends and improves the applicability of the empirical SWP prediction methods. This paper will use a portion of the recorded SWP data to benchmark existing SWP prediction methods and to establish improved resistance coefficients for the empirical method using a Monte Carlo type approach.

For the Westermost offshore wind farm assessed in this study, the findings show that the existing SWP prediction methods generally under predict the observed SWP. The results of the Monte Carlo type analysis show that the new resistance coefficients are generally lower than the generic resistance coefficients provided by DNV (1992). The results also show that the tip resistance in coarse grained materials and the shaft resistance in fine grained have the largest influence on the accurate prediction of the SWP.
HORA Hinge-Over Riser Assembly Riser System
Authors: Martins S. B. C. , Harris S. W. , Nakajima E.
Published: April 2017

HORA (Hinge-Over Riser Assembly) is a new riser system that improves the traditional Free Standing Riser (FSR). The system includes an articulated horizontal connection located at the base structure, eliminating the requirement for a subsea base jumper between the flowline and riser needed with the conventional FSR. HORA's key advantages compared to the traditional FSR system concept are: (1) shorter installation schedule; (2) increased reliability of the riser system; (3) increased operational flexibility and improved ability to respond to contingencies; (4) lower installation risk; and (5) reduced capital expenditure.

HORA incorporates two novel technologies. The first is a hinge-over system that enables seamless integration of flowline and riser pipelay tasks, also allowing the riser to be laid on the seafloor during installation. The second is a locking mechanism connecting the HORA in-line structure (ILS) with the foundation suction pile, effectively isolating the subsea horizontal connector from any loads that could potentially cause its failure.

This proprietary HORA Technology solution has progressed from the concept to maturity and is a viable option in offshore oil and gas field developments. During the design phase the major focus areas were to effectively isolate the horizontal connection from overstress and fatigue loads due to external loading, as it is the primary flow path component that enables the hinge-over function. In-place and installation analyses were developed to identify these loads and the ILS and locking mechanism were designed using finite-element models (FEM) to address them. FEM was also used to address the in-place riser and installation loads imposed on the hinge-over mechanism. In addition, an offshore installation method has been detailed and a failure modes, effects and critical analysis (FMECA) performed by an independent engineering organization.

HORA is an improvement from the traditional FSR concept and an alternative for offshore field developments and for specific scenarios and applications such as Marine Well Containment Systems (MWCS), Early Production Systems (EPS) or in areas prone to inclement weather, short installation windows or risky environment. This paper presents the engineering solutions to meet the performance targets defined for HORA Technology Development Project.
Fast-Track Development of Managed Pressure Drilling Flexible Mud Return Line
Authors: Szekely Gergely , Peixoto Eduardo , Czovek Zuzana , Mezo Tamas
Published: April 2017

In the oil and gas industry there is a common misconception that bonded flexible pipes designed according to the only approved standard for deepwater MPD applications, API 17K are overdesigned and heavy.

This paper is to clarify the misconception and present to the industry the flexibility that API 17K gives to tailor the hose construction reflecting the actual requirements and customer needs. Over the last few years a lot has been learned on the MPD operations, using inputs of the industry's major players, the hose requirements that in the past led to overdesigned, heavy and expensive flexibles have been revised, allowing a more efficient hose construction to be developed keeping the design premises of API 17K.

Brief overview on API specifications is given in terms of their applicability to MPD operations. Technical challenges and solutions are discussed in details for the flexible pipes carrying well effluents in kick situations with special emphasis on the importance of selecting the proper liner material. Gas diffusion phenomena in bonded flexible pipes is detailed. Technological advances are highlighted resulting meaningful weight and cost savings while not compromising on HSE and quality – meeting the stringent design and test criteria of API 17K. Results of the full scale tests demonstrating the hose performance are presented, such as bending stiffness test, blistering test and burst test.

This paper is providing an example of a quick turnaround research and development project of an equipment manufacturer with heavily integrating the feedbacks of the first years of MPD operations to result a fit for purpose and cost effective product.
Adding Thousands of Barrels for Little Cost in a Gulf of Mexico HPHT Deepwater Field, an Effective System Modelling & Optimization Case Study
Authors: Ogugbue Chinenye , Pietrobon Marney , Stewart Carlos , Duvivier Giles , Macnamara Robert , Bishop Simon
Published: April 2017

The Thunder Horse offshore Field, located in the Gulf of Mexico, consists of multiple producing complex oil reservoirs. The producing zones have been developed with approximately 20 wells flowing, via 5 subsea flowline-and-riser systems, into a dual train production facility.

The combination of risers, trains, and separation stages allows a wide range of routing flexibility and optimization opportunities for this production system. However, the complexity of the different combinations requires innovative system optimisation strategies to identify optimal configurations. An Integrated Asset Model (IAM) was built which achieves excellent fidelity and reliably predicts production improvements. One particular application of the IAM in 2015 informed the safe, reliable routing of a well directly to a second stage separation vessel resulting in the delivery of over 5 mbopd extra production. These techniques are now being applied to other BP assets with continued success.

This paper describes some key elements of these models, the challenges in maintaining and calibrating these models, and a case study to showcase its value.
Offshore Trinidad AWAC Wave Data Assessment
Authors: Mendelsohn D. L. , Fratantonio R. , Hanson J. , Bangs A. S. , Withall T. , Crosby A. R.
Published: April 2017

To support and facilitate deep-water operations, accurate measurements of metocean conditions are needed to assess constraints and provide criteria for offshore design and installation. BHP Billiton installed three deep-water (1,770 – 2,120m), taut-line moorings for 12-months in 2014-2015, offshore Trinidad and Tobago measuring waves, currents, salinity, and temperature to accomplish this task.

An associated metocean analysis was performed on the Acoustic Wave And Current (AWAC) sensor data, with supporting Navy Global Environmental Model wind data. The objective of this study was to analyze the AWAC data to understand the wave climate in the region, and specifically, to perform a wave partitioning analysis to compute time-evolving wind-sea and swell wave system parameters. The data set was then used to check analyses and predictions made in the development of operational and extreme metocean design and operational criteria. Taut-line moorings can periodically respond to forcing, dependant on mooring length, mass, buoyancy and drag, which can negatively influence measured directional wave characteristics. Analysis found that the natural mooring response frequency to periodic forcing was in the range of 140 s, outside the range of wave or current variability in the region.

Wind roses verify the predominance of easterly wind flow with corresponding waves roughly aligned. Bulk significant wave heights appear normally distributed with a median wave height of approximately 1.4 m. Peak periods are predominately 8-9 s, with occasional wave events to approximately 18 s period. Wave directions are east-northeast to east most commonly, and most energetic during winter and spring. There is an absence of waves from the south and west due to the blocking effects of Trinidad and South America. Peak wave events were identified with a peaks-over-threshold algorithm, for Hs > 1.5 sigma above the mean, showing a maximum event with Hs = 4.0 m and Tp = 10.6 s, and three events with Tp > 13 s at all 3 moorings with directions mostly from the northeast.

Wave spectra directional distributions at higher frequencies appeared compromised as a result of instrument deployment depths, affecting the horizontal spacing of near surface velocity cells used in internal AWAC processing. Modified spectral partitioning with high-frequency masking was developed to eliminate suspect frequencies from the analysis. Partitioning used an inverse watershed algorithm to isolate peak domains in directional wave spectra. Wind sea peaks were identified using directional wave age criterion. Wave component clustering was used to form time-evolving systems from the partition results. Resulting wave systems can be traced to a specific generation region on the ocean surface. Wave vector history plots showed that the Trinidad wave field was typically a mixed sea and regional swell field with occasional long-period swell events from distant storms.
Plastic Limit Analysis of Laterally Loaded Piles and Wells Conductors in Soil Profiles with Crust
Authors: Grajales-Saavedra Francisco J. , Aubeny Charles P. , Jeanjean Philippe , Drew Dane
Published: April 2017

This paper presents a series of studies in which traditional upper bound plastic limit analysis (PLA) methods are modified to accommodate non-linear strength profiles which correspond to soils with crust. The collapse mechanism presented comprises a surface failure wedge, a flow-around region and a spherical base failure surface. Results are compared to predictions from 3-dimensional finite element analyses for case of a surficial stiff ‘crust’ overlying a thicker layer of soft soil. An introductory discussion on the origin of such ‘crusts’ is included. Comparisons are presented in terms of both horizontal bearing capacity and lateral unit bearing capacity profiles, which are depth-dependent. A series of parametric studies is presented in which the effect of pile diameter and soil strength is assessed. The paper presents a simplified practical approach to calculate lateral bearing capacity factors for soils with crust, by modifying an existing solution for linear soil profiles.
Stability and Performance Evaluation of Hybrid Foundation System for Subsea Applications
Authors: Jang Sehoon , Suroor Hadi
Published: April 2017

A hybrid foundation system defined as the combination of shallow and deep foundations has been developed as an alternative to large diameter suction piles, to tackle ever increasing flowline walking loads in deep water subsea field developments. In the current environment of cost effective measures and continued expansion of offshore developments, a hybrid subsea foundation, typically consisting of a mudmat and corner pin-piles, can offer significant fabrication and installation cost savings, compared to traditional large diameter suction piles, as flowline restraint anchors. Since a hybrid foundation combines shallow foundation (i.e. mudmat) with deep foundation (i.e. pin piles); the current industry standards / guidelines do not provide any specific recommendations as to the design requirements of this complex foundation system. This study is primarily aimed to elucidate the performance and stability evaluation of the hybrid foundation based on the full 3 dimensional (3D) finite element analysis (FEA) results.

Since the emergence of this relatively new hybrid foundation concept, a limited number of technical papers have been published based on analytical, experimental as well as numerical approaches with no clear consensus in design principles. This comprehensive numerical study aims to bridge the gaps in the previous studies by developing 3D failure envelops (yield surface) to provide better understanding of the effects of multi-directional loadings on the capacity and displacements of a complex hybrid foundation system. The study also investigates the pattern of the soil resistance mobilization under various loading conditions to understand the soil-structure failure mechanism as well as displacements of the hybrid subsea foundation.
Heading Control of a Turret-Moored FPSO with and Without Forward Thrusters
Authors: Kaasen Karl , Ludvigsen Halgeir , Aas Kristian
Published: April 2017

A valuable property of a turret moored FPSO is its ability to weathervane or self adjust its heading to the varying metocean environment. Still, heading control with thrusters is necessary when a different heading than the natural weathervaning heading is wanted for operational reasons. In particular, in non-colinear metocean conditions it may be desirable to keep the bow of the FPSO against the waves to reduce rolling. It may happen that the weathervaning becomes unstable. In this case, the vessel will go into fishtailing motion, which is a phenomenon that is governed mainly by interaction between sway and yaw. Fishtailing is weather-dependent. When it happens, heading control is needed to stabilize it.

One important objective of the study has been to investigate if satisfactory heading control can be obtained using thrusters aft only, or if thrusters forward are necessary.

For a given FPSO design, we study weathervaning stability by formulating a linear model in sway and yaw. Based on this model with damping neglected, we develop three simplified criteria for stability. Using heuristic argumentation, we accept the criteria as conditions for sufficiency. The system's eigenvalues give sufficient and necessary conditions for stability. Using metocean hindcast data covering a time span of 56 years, the simple criteria are tested against the eigenvalues of the sway-yaw model. We found good agreement.

The heading controller used is essentially a PID controller. It is found that with aft thrusters only, good heading control can be achieved for all the metocean states in the 56 years span, provided the controller gain is moderate. With high controller gain, the thrusters may excite resonance in the turret mooring. Using additional thrusters forward gives the freedom to reduce turret resonance. Time domain simulation with an accurate 6-degree-of-freedom model shows that thrusters aft and forward gives slightly better control than control using aft thrusters only. Still, using only aft thrusters appears to give satisfactory heading control.
Real-Time Monitoring and Diagnoses on Deepwater Cement Barrier Placement: Case Studies from the Gulf of Mexico and Atlantic Canada
Authors: Contreras Jose , Bogaerts Martijn , Griffin Dave , Rodriguez Faiber , Sianipar Sakti , Villar Vitor , Taoutaou Salim
Published: April 2017

The updates in the US code of federal regulations 30 CFR Part 250 Oil and Gas and Sulphur Operations in the Outer Continental Shelf, released in 2016, relate to, among other things, real-time well monitoring on critical well operations including cementing. The regulations do not assume that onshore-based staff would assume operational control, but rather that onshore expertise can assist the offshore location in determining anomalies before they become critical issues. Currently, cement job monitoring is often limited to the acquisition of pressure, rate, and density measurements. Based on those measurements, a basic evaluation is performed during the job. A new software tool has been developed to improve the ability to interpret and diagnose critical job parameters while the cement job is in progress.

The real-time cement monitoring (RTCM) simulator combines data from the cement job design with acquisition data from the cement unit and rig to provide a detailed picture of the operation by comparing acquired values with predictions computed in real time. Data acquired during the cement placement are processed by a hydraulics simulator incorporated into the software to provide key information about the fluids' position in the annulus, comparative trends of acquired versus simulated surface pressures, density quality assurance and quality control, and real-time visualization of dynamic well security. Based on the real-time estimation of the fluids' position in the annulus and other key parameters measured during the job execution, a contingency plan can be followed, thus avoiding the need to wait on a detailed post-job analysis of the raw acquisition data.

This paper describes the methodology of the software and how it helps to diagnose the cement barrier placement in deepwater wells. The real-time monitoring of the cement job starts with the evaluation of the pre-job circulation and ends with the final displacement. With the real-time capabilities, experts can remotely view operations and provide recommendations during the cementing operations and immediately advise on post-cementing rig activities. Through case studies from the Gulf of Mexico and Atlantic Canada, the process and benefits will be shown to improve barrier verification as early as possible in the well construction phase.

The novelty of the software is that it can be used to diagnose the quality of cement jobs during the execution stage. Synchronized visualization of wellbore schematics showing fluids position, equivalent circulating density (ECD) progression, and combined measured versus simulated surface pressures are critical to help determine the position of fluids in the annulus and provide early verification of a barrier.
New Umbilical Manufacturing Method Eliminates Weight Limitation
Authors: Figenschou Arild , Hickman David , Høie Leif
Published: April 2017

This paper will present a new manufacturing method for Umbilicals. The new bundling principle presented here has eliminated the weight and volume limitations of the conventional systems. The conventional manufacturing method is to use a vertical or horizontal planetary machine which requires that the pay-off reels has a rotation about the centre of the umbilical during closing operation. Each of the planetary positions has a weight and volume limitation. The new manufacturing method, which is based on SZ stranding, is based on static pay-off reels and a static (non-rotating) closing point as opposed to the planetary system. This principle has been made possible by a periodically change in the lay direction during the bundling operation. Due to the long lay-length configuration, there are no requirements for a separate armour system as the internal elements carry the load without excessive rotation of the umbilical.
Qualification and Development of the World's First High Pressure Subsea Boosting System for the Jack and St. Malo Field Development
Authors: Hjelmeland Mads , Reimers Oeyvind , Hey Chris , Broussard Dan
Published: April 2017

The Jack and St. Malo fields were developed in a deepwater Gulf of Mexico (GoM) setting by Chevron and co-owners and commenced production in 2014. The reservoirs are located roughly 25 miles apart, about 250 miles southwest of New Orleans, Louisiana. Water depths in both fields are around 7,000 feet, and the reservoirs lie approximately five miles below the water surface. The Jack and St. Malo fields were developed with subsea completions flowing back to the Walker Ridge Regional Platform, the largest, by displacement, semi-submersible floating production unit (FPU) in the GoM.

The Lower Tertiary trend (LTT) in the GoM poses a number of documented challenges for flowing reservoir fluid from the sand face to surface facility. The key challenges are related to low permeability, high pressures, high temperatures, as well as water and well depths.

The naturally high pressures driving Jack and St. Malo fields during the early stages of development will decrease over time as the fields are produced. To compensate and maintain production levels, it was decided to deploy three powerful subsea pumping systems on the seabed to boost fluids from the wells to the host platform. While a number of subsea boosting systems have been deployed over the years, the Jack and St. Malo fields required technology qualification in order to meet design requirements in terms of water depth, pressure rating and shaft power.

This paper will describe the technology qualification program of the world's first high pressure seabed boosting system, as well as the subsequent delivery project and deployment of three subsea boosting systems in the Jack and St. Malo fields. An overview of the drivers for selecting this technology will be provided, as well as insight into early operational experience from the field.