bluuebunny/crossref_metadata_2025 huggingface dataset:
Smart Bentonite Drilling Muds Modified with Iron Oxide Nanoparticles and Characterized Based on the Electrical Resistivity and Rheological Properties with Varying Magnetic Field Strengths and Temperatures
Authors: Vipulanandan C. , Mohammed A. , Samuel R. G.
Published: April 2017

In this study, the effects of magnetic field strength and temperatures on the electrical resistivity and rheological properties of a sensing smart bentonite drilling mud modified with iron oxide nanoparticles (nanoFe2O3) were investigated. The bentonite contents in the smart drilling muds were varied up to 6% by the weight of water, and the temperature was varied from 25°C to 85°C. The magnetic field strength was varied up to 0.6 T. The nanoFe2O3 contents (particle size of 30 nm and surface area of 38 m2/gm) in the drilling muds were varied up to 1% by the weight of drilling mud to enhance the sensing electrical resistivity and the rheological properties of the drilling mud. The initial resistivity of the 2% and 6% bentonite drilling mud were 9 Ωm and 5.5 Ωm, a 39% reduction in resistivity, a good sensing property.

The electrical resistivity of the drilling mud modified with of nanoFe2O3 decreased by 15% to 50% based on the nanoFe2O3 content, temperature and magnetic field strength. The rheological properties of the drilling muds were characterized by high strain rate to determine the nonlinear behavior of the shear thinning drilling mud. Based on the new Vipulanandan rheological model, the yield stress (o2) of the modified drilling mud increased by 6% to 100% depending on the bentonite content, nanoFe2O3 content, temperature and magnetic field strength. Based on the Bingham plastic model the plastic viscosity of the modified drilling mud were increased by 50% to 90% based on the bentonite content, nanoFe2O3 content, temperature and magnetic field strength. The shear thinning behavior of the drilling mud with and without nanoFe2O3 has been quantified using the Vipulanandan rheological model and compared with the Herschel-Bulkley model. Based on the Vipulanandan rheological model the maximum shear stress produced (maximum shear stress tolerance) by the 2% bentonite drilling mud modified with zero and 1% of nanoFe2O3 at the temperature of 25°C with no magnetic field strength were 26 Pa and 64 Pa respectively. Increasing the magnetic field strength to 0.6 T increased the maximum shear stress produced by the 2% bentonite drilling mud modified with 1% of nanoFe2O3 at the temperature of 25°C to 80 Pa, a 25% increase. With the 6% bentonite drilling mud the trends were similar but the magnitude of the maximum shear stress produced was almost doubled. The rheological properties of the drilling mud modified with nanoFe2O3 under different magnetic field strength have been correlated to the electrical resistivity of the drilling mud using the three parameter Vipulanandan property correlation relationship.
Recent Advances in Nonlinear Soil Models for Fatigue Evaluation of Steel Catenary Risers SCRs
Authors: Clukey Edward C. , Zakeri Arash
Published: April 2017

The role of soil response on fatigue life of Steel Catenary Risers (SCRs) has been investigated through a scaled sectional SCR (cut-out section) in a geotechnical centrifuge. The SCR model simulated a section of the SCR starting at 16 ft (4.9 m) above the seafloor and extending approximately 360 ft (~110 m) through the touchdown region to the anchor point. The centrifuge tests were successfully performed using soils from the Gulf of Mexico (GoM) and offshore Angola. Past studies have demonstrated that fatigue damage in a full-scale SCR at touchdown zone can accurately be modeled using a scaled sectional SCR in a geotechnical centrifuge. The centrifuge results were compared to finite element simulations with the seabed response modeled using nonlinear springs derived based on unload-reload stiffness (secant stiffness) of degraded soil at steady-state conditions. This resulted in development of a simplified approach involving the nonlinear soil springs. Fatigue analyses indicated that this simplified approach can predict fatigue damage as measured in the SCR centrifuge tests. Centrifuge tests were also performed to determine the impact of trench depth on SCR fatigue. The tests involved a flat seabed and seabed with an initial prescribed trench. SCR fatigue damage in the test with an initial prescribed trench was similar to that of the flat seabed; however, the critical fatigue point had significantly shifted.
Hazard Quantification of Seismically Induced Tsunamigenic Subaerial/Submarine Mass Movements
Authors: Sancio Rodolfo , Rao Pramod , Hunt Christopher , Umberg David , Greene Alexander , Misra Shubhra
Published: April 2017

This study presents a simplified framework for the quantification of the probability of seismically induced subaerial and submarine mass movements, an essential input for assessment of tsunami risk. The study incorporates the probability of seismically-induced ground motions developed from a Probabilistic Seismic Hazard Analysis (PSHA) and the probability of landslide triggering given an input ground motion, to calculate the joint probability of seismically-induced mass movement.

Potential subaerial and submarine sliding masses of sufficient size to trigger a tsunami were identified through a geomorphological analysis of seafloor bathymetry and topographic relief coupled with available regional geological studies of the area. Typical slide volumes were in the range of 107 and 108 m3, consistent with the volumes noted during historical events.

In this study, the probability of triggering a mass movement was defined as the probability of exceeding a threshold seismically-induced displacement value along a defined sliding surface beyond which uncontrolled movement of the slide mass was assumed to occur, leading to the potential development of a tsunami wave. The probability of exceeding the threshold displacement was calculated using the Bray and Travasarou (2007) method for estimating earthquake-induced slope displacements.

The study treated uncertainty in the input parameters through the use of probability density functions developed using slope stability back analyses and engineering judgement. Material strength parameters were subsequently updated using Bayes theorem.

The results of the study indicated that seismically-induced mass movements with potential for triggering a tsunami wave would have an annual probability lower than 1·10−3. Some of the slide scenarios selected in the study were used by others as input into hydrodynamic analyses for tsunami wave generation and propagation, and subsequently to define design inundation levels and design wave events for marine facilities.
Cross Sectional Flow Modelling of a Drilling Riser System for Hydrodynamic Drag Consideration
Authors: Lai Lawrence S. H.
Published: April 2017

This study aims to characterize the hydrodynamic behavior of top-tensioned drilling riser joints with complex cross-sectional profiles when exposed to offshore current environments, such as slick joints and conventional buoyant joints. Computational Fluid Dynamics (CFD) has been employed to analyze these component cross-sectional profiles and define the component drag coefficients (Cd) and lift coefficients (Cl). These coefficients determine the riser external loading, which in turn affects the riser internal stresses. The Strouhal number St is also calculated which characterizes vortex shedding.

Validation of the CFD model is performed based on 2-dimensional flow past a cylinder. Following this, 2-dimensional representations of the detailed drilling riser components are created. The flow speed range considered corresponds to prevalent offshore environments, with Reynolds number (Re) = 105 – 106. The average forces are determined by subjecting the riser to various flow angles of attack across the 360 degrees range, giving the Re-dependent Cd and Cl. Variations in vortex-shedding is also analyzed by calculating St to demonstrate the effects of different flow attack angles.

Validation of Cd and St for flow past a circular cylinder show good agreement with literature. Variation of the riser component outer profile and flow attack angle show variation in the drag and lift force experienced as well as the vortex shedding behavior. More accurate Re-dependent Cd was produced for the various cross-sections analyzed that could be used in subsequent global riser analysis to simulate the full connected system from vessel, riser system, wellhead, and conductor and casing (interacting with the seabed).

Application of these more accurate drag coefficients result in more representative riser motions and loads in the global riser analysis. The benefit is potentially increasing vessel and operational uptime, and accurately calculating the drilling riser system fatigue life. Ultimately, this enables drilling operators and their stakeholders to make better-informed decisions on their offshore operations.
Design Methodology for Converting a MODU into a FPU
Authors: Moe Anders Martin , Laranjinha Manuel
Published: April 2017

There are many idle mobile offshore drilling units (MODU) that present potential opportunities to reduce the cost of field development. This paper summarizes the background and proposes a design methodology that can be applied when companies look into the potential of modifying semisubmersible MODUs to floating production units (FPU).

The focus will be on the relevant commercial aspects that need to be taken into account, followed by the engineering efforts required for modification of the hull and main marine systems and the replacement of drilling systems by process topsides. There are some key differences in the design drivers for semisubmersible MODUs and FPUs that need to be taken into account when considering a conversion. This further governs the requirements for modifications and upgrades of a semisubmersible MODU in order to operate as a FPU. Based on the above, a case study has been executed.

Expected required modifications and upgrades are outlined in the paper. Further, some options for improving payload capacity are presented and discussed in terms of cost, payload increase and overall impact on the FPU design. There are several technical and commercial aspects that affect the viability of converting semisubmersible MODUs to FPUs, including but not limited to: production capacity/profile, environmental conditions, existing infrastructure, mooring and riser system requirements, contractual model, CAPEX for MODU and conversion scope. On the basis of the above, and an overall assessment of the current market and availability of MODUs, a qualitative feasibility evaluation has been performed and is presented in the paper.

The need to reduce the cost of deepwater projects is vital if projects are to be sanctioned and move forward. We must find innovative ways to drive out cost if the industry is to survive. Conversion of MODUs to FPUs may prove to provide an opportunity to achieve this.
DeepStar® Study on Effect of Coupled Horizontal and Vertical Interaction of Steel Catenary Risers with the Seabed within the Touchdown Region
Authors: Sancio Rodolfo B. , Clukey Edward C. , Lekkakis Dimitris , Aubeny Charles
Published: April 2017

Steel Catenary Risers (SCR) are typically subjected to vertical and horizontal motions, as well as rotations, causing the SCR to interact with the seabed within an area described as the Touch Down Zone (TDZ). The interaction between the seabed and the riser at the TDZ induces bending stresses on the SCR that can have a significant impact on the fatigue life of the riser.

ROV surveys of installed deepwater SCRs show that, in soft clayey seabeds, SCRs cut deep and wide trenches into the seabed that are up to four or five pipe diameters deep and three to four pipe diameters wide. Despite the observed lateral interaction between the seabed and the SCR, the current standard of practice for fatigue analysis of SCRs, through commonly used design software packages, only considers the vertical interaction of the SCR with the soil in the TDZ, thus neglecting the effect of the lateral interaction between the SCR and the seabed and its potentially detrimental effect on the fatigue life of the riser.

A study was commissioned as part of DeepStar® Phase X to evaluate the effect of horizontal interaction between the seabed and an SCR. Quasi-static analyses were conducted using a finite element method based program by simplifying the interaction of the SCR and the sea bed as that of a beam resting on, and surrounded by, linear and non-linear springs. The von Mises stress range was calculated for conditions in which the SCR was subjected to vertical motions and to vertical and horizontal motions while varying: (1) the amplitude of the motion; (2) the undrained shear strength of the sea bed; (3) the initial embedment of the riser in the seabed; and (4) the boundary conditions applied to the SCR.

The results of our analyses indicate that, for the conditions that were studied, the effect of incorporating horizontal interaction between the SCR and the sidewalls of a trench on the von Mises stress range is typically less than 5%. The analyses also indicate that: (1) the effect of the lateral interaction of the SCR with the seabed increases as the amplitude of the vertical and horizontal motions increase; (2) the contribution of the lateral motion decreases as the soil strength increases and the soil stiffens; (3) the contribution of the lateral motion decreases as the embedment depth increases.

This simple study showed that horizontal seabed-SCR interaction may not have a substantial effect on the fatigue life of the SCR. However, other sea states, soil conditions, and geometries may show substantially different results that should be investigated.
The Dawn of the New Age of the Industrial Internet and How it can Radically Transform the Offshore Oil and Gas Industry
Authors: Sharma Partha , Hamedifar Hamed , Brown Aaron , Green Richard
Published: April 2017

Rapid advancements in big data management, digital connectivity, low-cost sensor technologies and high-performance computing, are ushering in the fourth industrial revolution: the Industrial Internet. This paper provides an overview of the Industrial Internet and the infrastructure implementation challenges for the offshore oil and gas industry.

The application of the Digital Twin for Asset Performance Management and Real-time Facility Risk Management is described in the paper. The Nauticus Twinity use case for performance management of a supply vessel demonstrates the benefits of a digital twin. Finally, the paper elucidates the challenges of implementing machine learning models in operations to improve asset performance.
Resolving the API RP 2MET Crest Conundrum for Wave-in-Deck Loading
Authors: Santala Markku J.
Published: April 2017

The API recommended wave load recipe is based on a "design wave approach" which uses a nonlinear regular wave theory such as Stream Function. When using such a nonlinear regular wave theory, a wave with a specified height, period and current has an associated crest that can be deterministically computed. In a random seastate, crest elevations are not deterministically associated with combinations of wave height and period and the highest individual crest is not always associated with the highest individual wave height. In general, the N-year crest elevation estimated using realistic wave distributions is not the same as the crest of the N-year wave. Hence, when computing global loads in an inundation situation, analysts may be confronted with the "crest conundrum" whereby the crest of the N-year wave that they regularly use to compute global jacket loads may not have an associated crest elevation which gives the inundation level indicated by the N-year crest. This paper documents the method recommended by the API Metocean Committee to resolve this so-called "crest-conundrum" and discusses validation of the method over the full range of relevant Gulf of Mexico conditions specified in API RP 2MET.
Standardization Benefits for Megaprojects, Illustrated by Motor and Drive Case Studies
Authors: Ward Stephen , Jackson Eur Ing Steve
Published: April 2017

This paper discusses standardization benefits for megaprojects drawing on first hand experiences from actual executed global projects and the collected opinions of End Users and Engineering Procurement Contractors (EPCs).

Megaprojects are characterized not only by their huge scale but also through the many global parties required to execute and the number of partners involved in funding and finally operating the constructed enterprise. All these relationships mean difficult agreements on preferred vendors and specifications which can lead to multiple competitive bids to satisfy perceived ‘lowest' cost requirements. However, some studies have indicated that an additional 100% man hours is spent on engineering products to meet special project specifications rather than use industry standards. This is compounded when these particular project requirements have to be enforced across a number of different vendors for similar equipment. Consequently there is an industry-wide trend towards simplification and standardization not only to a small number of vendors on a project, but also to use as close to accepted industry and vendor norms wherever possible.

Supplying motors and drives to global oil and gas, megaprojects is a complicated business because the equipment is not purchased directly by the EPC or the End User. Typically motors and drives are packaged by the compressor, pump, fan, hoist, HVAC etc. Original Equipment Manufacturers (OEMs) who may be myriad in number and located in various other different countries. Standardization provides significant CAPEX and OPEX benefits as well as reduce risk and man hours during project execution. In some cases it has been calculated to save as much as 14% of the total motor and drive project spend.

The Main Motor and Drive Contractor (MMDC) methodology has been used successfully to provide simplification, standardization, reduced cost, less effort, fewer interfaces and lower risk on a number of megaprojects.
AC Subsea Power Transmission Architectures, Design And Challenges, The Martin Linge Case
Authors: Skaanoey Thomas , Kerin Uros , Van Luijk Nico , Thibaut Edouard
Published: April 2017

The development in subsea technology relies increasingly on sophisticated and power-intensive equipment, such as pumps, compressors, processing, and flow assurance systems, for which there is a growing need to provide ultra-reliable electrical power transmission, distribution and conversion systems in order to supply subsea processing equipments through long step-outs.

In May 2015, the 163km long Martin Linge submarine cable was successfully energised and tested, setting the world record for the longest High Voltage AC (HV AC) subsea cable. This key achievement has demonstrated the feasibility and maturity of AC subsea power transmission for long stepouts. The next technical challenge would be to develop and mature a concept where the full field development is made subsea, whilst using power from shore through a long AC step out.

This paper provides an overview of potential architectures for long step-out subsea electrical power transmission and distribution systems. The paper describes the design and main technical challenges of the Martin Linge AC transmission step-out. Finally, the paper provides an insight in the point of view of the manufacturer and operator, with lessons learned in a successful development of a power from shore solution.
Cleanup of Organic and Inorganic Wellbore Deposits Using Microemulsion Formulations: Laboratory Development and Field Applications
Authors: Quintero Lirio , Ponnapati Ramakrishna , Felipe Mary Jane
Published: April 2017

Progressive reduction of the flow path of oil and/or gas in the near-wellbore region could cause a gradual decline in hydrocarbon production. The major parameters that influence the time-frame of this process are related to the properties of the crude oil and to the reservoir pressure and temperature. Failure to achieve expected well production could also occur, suddenly, after a well intervention or after the wellbore construction. In either case, changes in pressure, temperature, fluid composition, incompatibility of fluids and/or poor fluid-rock interaction can generate precipitation and deposits of asphaltenes and paraffins, scale formation, emulsions or sludge and wettability alteration.

In general, traditional treatments do not target all possible causes of crude oil flow-path reduction at the same time, and a sequence of treatment fluids are pumped to clean up the multiple damages (e.g., treatment of organic deposits followed by an acid treatment to remove scale deposits). The long cleanup time and high volume of fluids used in a multi-step treatment could impact the economics of the projects, especially offshore.

The present work discusses multifunctional treatments for production enhancement and flow assurance that can remove organic deposits (e.g., paraffins and asphaltenes), emulsion blockage, scale deposits and increase water-wet condition of the flow path surfaces in one step.
Real Application of Electric Controls Technology to Subsea Systems: Success, Learnings and Recommendations
Authors: Johansen C. , Rokne Ø. , Moe S. , Magnus H. , Monsson O.
Published: April 2017

This paper explores the current history of subsea electrically driven functionality as well as provides recommendation to the industry on how to move forward. This history includes the drivers, features, field experiences, evolving cost picture and the success and failures of the products created during this 15-year journey. What has led the industry towards the solutions developed, how have those solutions lived up to their promises as far as lifetime and reliability are concerned? Why was it beneficial to store electric energy in batteries subsea for the operation of the system? and what should we consider going forward in how the industry should specify new technology?
All-Electric as an Enabler for More Cost Effective Developments on Cluster Systems
Authors: Winther-Larssen E. , Massie D.
Published: April 2017

Objectives

There is an increased need for cost effective subsea technology to enable oil companies to have more flexibility in system architecture and also enable access to developments in deeper water and with longer step-outs than before. As the current subsea production systems struggle to meet those challenges, the need for a suitable, flexible and cost efficient technology has emerged. All-Electric systems have this capability. By using the Aker Solutions developed portfolio of products and concepts this paper will show cases of simplified, easy integratable and cost reduced All-Electric solutions that can be installed independent of depth.

The paper will also touch upon the advantages of All-Electric systems in terms of reliability compared to traditional electro/hydraulic systems.

Methods, Procedures, Process

By integrating automotive and telecom competence with subsea expertise, it has been possible to implement a rigorous design-to-cost mind-set in the development of the various All-Electric system building blocks.

All-Electric hardware and software will give large benefits in terms of OPEX and be competitive in CAPEX (in addition to enabling improved environmental impact, increased levels of safety and increased functionality).

Some of these benefits will be further enhanced when applying subsea and downhole All-Electric technology solutions on a wider scale.

Results, Observations, and Conclusions

The paper explores the potential benefits an All-Electric system can have both in relation to CAPEX and OPEX.

Novel/Additive Information

Electric actuation, sensing, integrated power management and control offer the promise of smaller, lighter and more cost effective subsea production systems. They also offer the potential for more precise measurement, control and maintenance monitoring over time compared to their hydraulic counterparts, which enables planned maintenance of equipment, with significant benefits in terms of reduced OPEX.
Soil Model Assessment for Subsea Wellhead Fatigue Using Monitoring Data
Authors: Mercan Bulent , Chandra Yenny , Campbell Mike , Ge Michael Long
Published: April 2017

A significant effort is made by the industry through analyses and field monitoring to ensure delivery of safe and reliable wells. Fatigue analysis is an important aspect of well integrity assurance. Structural fatigue damage arises from stress changes caused by environmental cyclic loads acting on the riser system. In practice, the conductor-soil interaction under cyclic loading is modeled using the soil resistance-displacement (P-y) springs. Use of an appropriate soil model is essential for accurate determination of the fatigue damage. The American Petroleum Institute recommendations (API 2011) for P–y curves, which are often used for conductor–soil interaction analysis, have originally been developed for piled foundation and are inappropriate for well fatigue analysis. To that end, a new approach was developed by Zakeri et al. (2015) to derive P-y curves specifically for well fatigue analysis. Ultimate performance of each soil model can be determined and verified with field monitoring. This paper presents results of a field monitoring campaign for a well drilled in 354 ft water depth within a complex seabed stratigraphy comprising sands (loose to dense) and clays (very soft to stiff). Design, calibration and verification of the riser/conductor structural model using field data are presented in a companion paper (Ge et al. 2017). Herein, the effect of soil modeling on wellhead fatigue is discussed and predictions made with the API (2011) and the Zakeri et al. (2015) soil P-y springs are compared to field monitoring data. For the case presented herein, the results indicate that the Blowout Preventer (BOP) stack motion response is significantly affected by the soil stiffness and modeling methods. The predictions made with the Zakeri et al. (2015) model provided BOP response similar to those observed in the field both above and below the mudline. Whereas, the analyses done with the API (2011) model significantly overestimated the ‘measured’ conductor fatigue life above the mudline and underestimated it below. The results of this monitoring program are a step forward in better understanding system behavior of offshore wells.
Axial Compression Fatigue in Long-Lay-Length Fiber Mooring Ropes
Authors: Flory John F. , Banfield Stephen J. , Ridge Isabel M. L. , Carr Robert
Published: April 2017

Rope failure due to axial compression fatigue was found in two recent rope investigations. One of these was an HMPE mooring line on a gas carrier and the other was a nylon SPM hawser. In both incidents, the unusual rope design, with very long rope and strand lay lengths, was the root cause of the failure.

This paper first describes axial compression fatigue and how it can occur in fiber ropes. It briefly discusses a past failure of an aramid rope caused by axial compression fatigue. It describes the two more recent failure incidents. It describes how long-lay-length rope designs caused or contributed to the axial compression fatigue which resulted in rope failure.

This paper describes the axial compression fatigue test method. It reviews the axial compression fatigue performance for aramid and HMPE yarns from the Fiber Tethers 2000 JIP and presents new data for HMPE yarns and also for nylon yarns, which have never before been tested for this property.

Recommendations are made for fiber rope designs. Unless they are properly designed for the application, ropes with long rope lay and long strand lay lengths should not be used in the following situations: *Cyclic tension with many cycles down to low trough loads.*Cyclic bend over sheaves.*Cyclic rotation of the rope.
Wave Energy Converters and Tidal Energy Converters Road to Commercial Viability
Authors: Gehring Donald H.
Published: April 2017

This paper will report on the status of the US power industry today and how close some Marine Energy Converters (MECs) options are to becoming commercially viable in the near future. The paper provides an overview of the rules and regulation that have been written in preparation for MEC entries into the power market place, some of the costs of full scale Wave Energy Converters (WECs) and Tidal Energy Converters (CECs), how these costs compare to existing new power plant options and some new promising lower cost MEC developments to look for in the near future.
Time Lapse 4d Assessment of Shallow Water Seabed with Repeated Multi-Beam Hydrographic Surveys
Authors: Geldof J -B. , Naankeu-Wati G. , Labaune C.
Published: April 2017

Characterization of coastal erosion is paramount to ensure the integrity of any oil and gas facilities. Geophysical surveys are mandatory to build ground models of these particular areas to understand sediment movements and control the risk for the coastal infrastructures safety.

Based on past experiences, infield acquisitions and interpretations have fundamentally been improved to acquire recurrent high precision Multi Beam Echo Sounder (MBES) data with the objective of 4D interpretation. Using a recently developed algorithm addressing budget error (Naankeu-Wati et al., 2016), measurement uncertainty of bathymetric soundings has been thoroughly evaluated.

Beside the description of innovative acquisition methods, new data interpretation and processing techniques are revealed. For a particular area of interest, the paper shows the essential role of digital geographic tools and particularly Geographical Information Systems (GIS) to interpret 4D hydrographic data. Based on the Bathymetric Position Index (BPI) algorithm, a workflow has been built to automatically map seabed features such as sand waves from time-lapse dataset. Such automatic mapping method affords improving the quality of seabed features comparison through the time by limiting subjectivity of data interpretation.
Baseline for Planning and Cost Estimation of Brazilian Decommissioning
Authors: Mimmi F. , Ralston S. , Silva M. Miguel , Silva P. Martins
Published: April 2017

Decommissioning and abandonment of Brazilian offshore oil & gas fields has become more important in the last few years due to the maturing hydrocarbon producing basin in the region. However, a complete abandonment of a Brazilian offshore field has not been completed to date and the consequent lack of a reference case leads to uncertainties with operators and stakeholders during the conceptual phases of abandonment, when identifying the best decommissioning option and estimating a reasonable cost for the complete program of decommissioning activities.

This paper aims to satisfy this uncertainty and develop a Brazilian baseline for front end planning and cost estimation of the decommissioning, removal and disposal options.

The methodology presented in this paper is based on analysis of the national and international regulations applicable to decommissioning, the expectation of stakeholders and national supply chain benchmarking. Drawing on the conclusions of this analysis, the paper then presents the available decommissioning options generally applicable for fixed platform, floating platforms, pipelines and subsea facilities. The eligibility of each decommissioning option is then investigated against the background of current Brazilian regulatory requirement, highlighting those cases where the options are not mentioned in the legislation or where contradictions exist. Further analysis of the options is then undertaken to determine the preferred solution from the stakeholder perspective and to also define national supply chain benchmarking of the options to confirm whether the national supply chain can support the future potential demand for decommissioning in Brazil.

Finally, the paper shows a comparative case study for the high-level planning and cost estimation for the decommissioning of a complex of small fixed platforms including the plugging and abandonment (P&A) of the platform wells.
Design of the Disconnectable Buoy Turret Mooring for the Turritella FPSO
Authors: Leverette Steve
Published: April 2017

The Stones Field FPSO design provided many challenges in the design of the disconnectable Buoy Turret Mooring (BTM), including the 2900m (9500ft) water depth (the world's deepest floating production system), the first use of steel lazy wave risers from a BTM system, the local environment which included Rossby Topographic Wave currents along the Sigsbee Escarpment, and especially the efficient and safe mating and un-mating of two large floating bodies at sea without use of support vessels.

The paper covers the overall philosophy of the disconnect/reconnect operation of the turret/buoy, and then describes the major design challenges encountered. The major system components will be described. The functional aspects of the disconnection and reconnection will be discussed, with discussion of how the particular challenges of the project drove the design.

A sequence of increasingly complex model tests was used to guide the design. These initially included forced motion and drop tests to define the hydrodynamic properties of the buoy and the hydrodynamic near-field interaction of the buoy and a fixed FPSO turret. Later tests modeled the full system in waves while disconnecting and reconnecting. The model test results were then used to calibrate a numerical simulation which was used to refine and validate the design. A follow-on paper by Carrico and Leverette (2017) describes the test programs in detail.
Stones Development: A Pioneering Management Philosophy for Enhancing Project Performance and Safety
Authors: Lohr Curtis , Pena Maria
Published: April 2017

The Stones Project is Shell Offshore Inc.'s ("Shell") play opener discovery in the outer Lower Tertiary trend in the Gulf of Mexico ultra-deep water (~9,500 ft. water depth). The initial plan is a phased development, with an FPSO and 8 initial wells for Phase 1, potentially followed by a Phase 2 development after field performance is confirmed. The Stones FPSO is the deepest floating production system in the world. This paper will provide an overview of the Stones project, discussing the challenges that had to be overcome and the innovations that were developed to successfully deliver this ground breaking project.
Pipe-Soil Structure Interaction: Best Practices for Spools, Buckle Initiators, End Connections and Sand Waves
Authors: Bransby M. F. , Ramm M. , Zhou H. , Low H. E. , Fugro A. G. , White D. J.
Published: April 2017

Pipe-soil interaction behavior forms a key input into the design of pipelines. The global response of the pipeline can be critically affected by the resistance provided by the seabed. Accurate modeling of pipe-soil interaction behavior leads to improved reliability and can lead to design optimizations that offer considerable cost benefits.

Extensive recent research and advances in design approaches, particularly through the development of high pressure high temperature lines, has led to significant revisions and improvements to pipe-soil interaction modeling over the past decade. There are now well-established techniques for estimating the as-laid embedment and axial and lateral pipe-soil interaction responses – the non-linear ‘springs’ used in pipeline structural modelling – for pipelines laid on the seabed. However, these methods, as applied in practice, generally involve the key assumption that the pipe exerts a vertical force on the seabed, V equal to its submerged self-weight, W – the ‘V=W assumption’. However, this assumption is not appropriate for pipe elements that are close to points of fixity, constraint or vertical upsets – e.g. in-line tees, buckle initiators and sand waves – or which form spools.

This paper illustrates examples of all of these situations, showing pipe-soil interaction ‘springs’ generated with and without the ‘V=W assumption’, to show the contrasting behavior. Recommendations are provided for practical modeling of this soil-structure interaction behavior.

In some design scenarios, the pipeline may be sufficiently robust that adoption of the ‘V=W assumption’ may not affect the integrity of the design. In other scenarios, it may be necessary to eliminate the ‘V=W assumption’ in order for a satisfactory design to be demonstrated. This may be achieved by performing integrated soil-structure interaction analyses, or through iterative refinement of the pipe-soil ‘springs’. In all cases, an awareness of the ‘V=W assumption’ is required across the pipeline engineering and geotechnical teams, who should interact to determine the appropriate basis to demonstrate an acceptable design.
The Application of Fibre Optic Instrumentation for HPHT Pipeline Bundle Health Monitoring
Authors: Hendawy Mostafa M.
Published: April 2017

The present work addresses the results of the qualification testing of a fibre optic instrumented pre-tensioned bundle pipe-in-pipe (PIP) section, to provide a real-time integrity tool for pipeline bundle health monitoring. The aim of the testing is to allow the pipeline bundle system to be a cost-effective solution for subsea developments, unlocking high pressure/high temperature (HPHT) fields rated up to 220°C and providing thorough life assurance of the pipeline bundle system performance and integrity.

In line with Subsea 7's pipeline bundle research and development programme, the most recent trial at Subsea 7's Wester Pipeline fabrication facility, North East of Scotland was carried out on a 170m long bundle PIP section to demonstrate the capability of the fibre optics to detect different thermal and mechanical loads. The test commenced with a pressure strength test at 287bar, followed by three pre-tensioning cycles using a jacking system. The bundle PIP section then undertook two cycles of combined HPHT application. In addition, a 300mm high boulder bend was applied to the pipeline at pressure and temperature to verify that the compressive loads are too low for buckling to occur. The applied loads and the bundle PIP responses have been monitored in real-time using fibre optics and strain gauges for verification, in the presence of a third party. The test results were successful and are presented and discussed herein.

It has been found that the monitoring solution can be used to measure pre-tensioning construction load cycles accurately by detecting and recording strain levels up to approximately 1600με at the maximum pre-tensioning load with a high resolution. It can also monitor combined operational loads: pre-tensioning tension/compression, boulder case bending, thermal expansion and pressurisation up to 193bar at temperatures up to 220°C. The bundle PIP section endured all those loads safely and the fibre optic recorded data was in line with that recorded by the strain gauges, as well as the theoretical and FEA model results. Furthermore, the result dataset shows high consistency and repeatability at different loading combinations.

The value of this monitoring tool appears in the associated low cost and minimal risk in the use of the fibre optic technology to provide continuous real-time health monitoring and pinpoint the location on the pipeline bundle, at which an abnormality is present. Additionally, the fibre optic monitoring, demonstrated herein, is used to ensure the accurate input of the pre-tensioning into the pipeline bundle, allowing its use for HPHT fields.
How the Application of LGS Technology for Drilling Risers Reduces Drilling Costs Through Improved Operability
Authors: Kurts P. , Marcollo H. , Potts A. E. , Johnstone D.
Published: April 2017

Drilling risers are regularly deployed in depths beyond 5000 ft with large sections covered in buoyancy. The smooth cylindrical shape of buoyancy modules can result in significant VIV response, causing overall amplification of drag experienced by the riser. In turn, operations can be suspended due to drag effects on top and bottom angles; high current speeds can lead to a halt in operations, even complete disconnection and retrieval of the riser string. Although suppression technologies exist to reduce VIV response (helical strakes/fairings), these have not been integrated into the manufacture of buoyancy modules for practical reasons (stackability, ease of manufacturing/assembly/installation). Innovative Longitudinally Grooved Suppression (LGS) technology has recently been developed and tested with two main bodies of work undertaken; model testing and full scale numerical modelling. This paper covers the methodology and results of full-scale OrcaFlex/SHEAR7 simulation work performed on drilling risers in realistic current profiles for the Gulf of Mexico (GoM), concluding with the impact this technology could have in reducing costs by increased operability for drilling risers. LGS technology provides significant reduction in VIV response whilst maintaining similar buoyancy to conventional modules. Significant reduction in VIV response has multiple benefits: less drag, reduced fatigue damage, and an increase in maximum currents drilling risers can be operated in - without any moving parts or extra deployment installation time. High Reynolds Number model testing results showed LGS technology behaved favorably in observable repeatable conditions, whilst the full scale numerical modeling demonstrated how these parameters measured in model testing can be used to perform numerical modelling of full scale offshore drilling risers in a variety of water depths and conditions; improving operability and riser fatigue life. Operability during GoM eddy current events was calculated to increase 30% annually, equating to estimated annual savings of over $10M, with potential to save similar amounts within a short period in the case of extreme current events. By applying LGS technology, significant financial savings can be achieved through increased operability and increased fatigue lifetimes.
Air Gap on Semisubmersible MODUs Under DNVGL Class - Current & Future Design Practice
Authors: Pessoa J. M. , Moe A. M.
Published: April 2017

In light of recent incidents involving wave impact on the deck box and superstructures of semisubmersible MODUs there has been significant effort in reviewing and revising the regulatory regime governing the air gap of such units. An Offshore Technical Guideline (DNVGL-OTG-13) was published in draft edition by DNVGL in autumn 2016 with guidelines for air gap calculations that present several changes to what has been considered industry practice. This paper will, based on a generic semisubmersible MODU design, investigate the differences between what has been considered industry practice and the new guidelines. Focus of the evaluation will be on calculation of the wave-frequency contribution, namely on wave asymmetry factor and viscous damping influence on results. Further, the low-frequency contribution will be investigated. Results calculated using a fixed roll/pitch angle suggested by DNVGL are compared to results attained by calculating the actual low-frequency motions due to waves and wind. Low-frequency wave-induced exciting moments calculated with Newman's approximation and the full QTF are compared to assess the approximation's validity for this problem. Finally a full air gap analysis based on what has been considered industry practice and the new OTG-13 practice will be performed and compared with the aim of assessing the short term impact to the industry.
Seismic Response Spectrum in Lieu of Time History Analysis for Subsea Structure Design
Authors: Wang George , Loh Michelle , Peng Yen-Tun , Shen Joanne , Genesis P. E. , Malachowski Jim
Published: April 2017

With oil and gas exploration venturing into more seismic prone regions for global deep water developments, seismic assessment of subsea structures becomes a fundamental part of the design requirements of regulations, industrial codes and standards. This paper demonstrates a response spectrum analysis approach for the seismic design of subsea structures. Response spectrum analysis using commercially available dynamic software package is a time-saving and preferred method for the design of subsea structures as compared to the time history method for the seismic assessment. The study also intends to contribute to the standardization of the seismic design procedure for subsea structures.

The paper selected a typical subsea valve skid with a mudmat foundation for the seismic response spectrum analysis. Upper and lower bound values of soil springs were included to capture the response in relation to varying degrees of soil strength. To benchmark the time-saving advantage of response spectrum analysis, time history seismic analysis is also performed in parallel on the same subsea structure. Results of the two methods are compared to establish a technical position that the response spectrum is a more favored and efficient approach as compared to time history for the design of subsea structures.

For the subject structure, the response spectrum analysis results show that the structure remains elastic during ELE (Extreme Level Earthquake) and ALE (Abnormal Level Earthquake) seismic events. This is due to the low-rise geometric profile of subsea structures. The results also indicate that the response spectrum approach enables a faster and relatively accurate estimate of structural response with ELE/ALE loading while still using a linear method.

The response spectrum analysis serves to bridge the gap between a rough approach of directly applying a simple additional seismic acceleration on the structure, versus subjecting the structure to a time-consuming time history analysis. This time history analysis is not deemed necessary due to the smaller sizes hence the less substantial inertia loads of the subsea structures as compared to typical offshore platforms. Further studies in the future should be able to provide more "accuracy vs. efficiency" type of trade-off information on a wider range of different subsea structures.
Improving Reliability of MODU Mooring Systems through Better Design Standards and Practices
Authors: Ma Kai-tung , Garrity Robert , Longridge Kent , Shu Hongbo , Yao Aifeng , Kwan Tom
Published: April 2017

With a goal to improve the overall reliability of moorings used by MODUs (Mobile Offshore Drilling Units), this paper reviews gaps and issues in design standards and operation practices. MODU moorings stay at one location for a short term, compared to tens of years for permanent moorings on production facilities. While the exposure time to the environment is relatively shorter, mobile moorings have been seen to experience a sizable number of failures ironically. Probability of failure has been high on the order of 10−2. Improving reliability of MODU moorings may be achieved through two sides, i.e. better design standards and more rigorous operation practices. On the design side, there appears to be a lack of clear guidance on designing a mobile mooring system to a proper return period. The gap is prominent especially for moorings in tropical cyclone (aka hurricane or typhoon) areas. Current industry codes and standards do not have a clear guidance on what return period shall be used as a minimum to account for the risk associated with close proximity and failure consequence. Some guidance is provided in API RP-2SK, but it is limited to applications in Gulf of Mexico. This paper attempts to close the gap by proposing minimum return periods to be used and requiring a quantitative risk assessment (QRA) to justify the numbers for any region with tropical cyclones. Guidance on performing a QRA is provided, and aspects on how to produce trustworthy results are discussed. On the operation practice side, issues and gaps are identified and reviewed. Often times, MODU moorings do not receive a sufficient amount of attention in system design, deployment, inspection, and equipment maintenance. Common issues are summarized to raise awareness and best practices are presented.