bluuebunny/crossref_metadata_2025 huggingface dataset:
Subsea Separation - Advanced Subsea Processing with Linear Pipe Separators
Authors: Prescott N. , Mantha A. , Kundu T. , Swenson J.
Published: April 2016

Production fluid typically leaves a well in multiple phases, including: oil, gas, water, and solids. It is necessary to separate these components in order to recover the oil and gas, treat the water, dispose of sand, etc. In the past decade there has been a trend to move processing equipment to the seabed. As offshore production continues to be developed in deeper water, it is imperative to develop separator technology that will be designed for the hydrostatic forces and large amounts of produced water that is expected to occur over time.

This paper explores two novel subsea linear pipe designs that allow subsea processing to be accomplished more cost effectively than existing technologies. The process undertaken for designing the two novel subsea linear pipe separation technologies: (gas-liquid) and (gas-liquid-solids) is described. To validate the efficiency and effectiveness of these two systems, a Computational Fluid Dynamics (CFD) analysis and cost analysis have been performed for each separator to provide both a realistic view of the actual separation efficiency of the systems, as well as comparative cost efficiency to existing technology in use today. Separators utilizing the pipe classification can be made lighter and cheaper when compared to existing subsea separation modules. In addition, they can be fabricated out of standard pipe sizes, thus cutting costs due to high availability and ease of fabrication. These factors are made even more attractive when modularized for ease of installation and field expansion.

Applications of the process and design of these special separators are discussed along with their potential advantages in offshore deepwater seabed based developments. With continued research and testing, the gas-liquid and gas-liquid-solid linear pipe separator designs have the potential to reshape the subsea separation industry.
A Paradigm Shift in Subsea Technology Research and Development
Authors: Anikpo Afam
Published: April 2016

Crude oil prices are in the doldrums, major capital projects are being rolled back due to reduced commercial viability and the overall health of the oil and gas industry seems to be hanging in the balance. Contrary to popular notion, the timing could not be better to review the less than convincing industry approach towards research and development of new technologies.

This paper presents a review of the technology research and development process in the oil and gas industry, with emphasis on subsea technologies. It also investigates the approach towards technology advancements in other technology-driven industries such as Aerospace, Telecommunications and IT. It juxtaposes the findings of this investigation with the oil and gas industry. It discusses the key drivers, benefits, risks and overall strategies associated with technology development and adoption across these industries.

The investigation reveals a fundamental flaw in the approach to technology research and development in the oil and gas industry. The lessons learned from drawing parallels with other technology-driven industries are used to propose a new approach to subsea technology research and development.
A Complementary Safety Tool for Blowout Preventers
Authors: Rojas F. E. , Slocum A. H.
Published: April 2016

Hydrocarbon exploration and production relies on Blowout Preventers (BOPs) to prevent catastrophic accidents; however, currently there are no in-situ or rapidly deployable backup systems for BOPs. This paper presents a method and machine for predictably stemming an uncontrolled flow resulting from a failed Blowout Preventer. The tool, referred to as the "Hampering Active Wellbore Kit" (HAWK), is a machine that can feed wire (with varying material properties along its length) through a BOP's existing ports and into the wellbore. The wire, initially stored in spools inside the device, forms a tangled wire mass (TWM) inside the wellbore that serves to gradually stem the uncontrolled flow. A design theory is described for wire feeding in order to form a TWM in a free flowing conduit, and the efficacy of the method is evaluated by comparing flow rates of a single wellbore before and after the introduction of the TWM. A prototype machine for direct attachment to a BOP as a backup safety system is presented based on operating constraints and industry requirements.
Field Studies of Microbiologically Influenced Corrosion of Mooring Chains
Authors: Witt Devin , Ma Kai-Tung , Lee Tim , Gaylarde Christine , Celikkol Sukriye , Makama Zakari , Beech Iwona
Published: April 2016

Severe corrosion found on steel mooring components (CSMC) at several sites worldwide has caused concern in recent years as to whether the components can safely meet their design life. A pilot study was initiated to understand the underlying corrosion causes with the aim of developing successful CSMC mitigation methods. In 2014, a field test was conducted offshore at two different locations in West Africa in order to confirm the contribution of microbiologically influenced corrosion (MIC) to CSMC. The study provided evidence that MIC is a root cause of the observed severe corrosion in the form of mega-pits at one of the two test sites. The tests consisted of deploying carbon steel coupons on a fiber rope, herein referred to as a "microbial baiting kit", at facilities near the mooring systems to capture the biofilm forming microorganisms. The kit was submerged approximately three meters below the water surface for an extended period of time allowing for free swimming microorganisms to colonize the coupons. The kit was the first of its kind to be used in the industry for investigating MIC of mooring systems. Upon recovery of the coupons, pitting damage was revealed underneath the fouling deposits. Following DNA extraction, subsequent analysis of sequences representing fragments of the bacterial 16S rRNA gene demonstrated that, regardless of the test location, the outer part of the biofilm formed on coupon surfaces had significantly different microbial community structure when compared to the surrounding seawater. In both test sites, biofilm DNA analysis confirmed that obtained bacterial sequences represented the initial colonizers of submerged structures in marine environments. Sequences identified as belonging to sulfate-reducing bacteria (SRB), which are considered major contributors to MIC in suboxic/anoxic aquatic environments, were more abundant in biofilms but scarce in water samples. A higher number of SRB sequences were associated with coupons retrieved from the test location where pitting attacks were prominent. Sequences indicative of acetic acid-producers and non- SRB hydrogen sulfide-producing microorganisms, that are also likely MIC contributors, were identified; however, further work is required to prove the involvement of these prokaryotes in steel deterioration. The results and finding from this pilot work set the stage for a comprehensive Joint Industry Project (JIP) launched by DeepStar® and is entitled DeepStar® CTR12402 Integrity Management of Mooring Systems Against Corrosion JIP. The aim of the DeepStar® JIP is to determine possible measures of MIC mitigation.
Realtime Monitoring, Using All Available Data, Plays A Vital Role In Successful Drilling Operations
Authors: Moore Cory , Doyle Eamonn , Jewula Karol , Karda Lukasz , Sheehy Tim , O'Connor Stephen , Djordjevic (Obie) Obren
Published: April 2016

In order to mitigate predrill uncertainties and provide the well team with the best information to drill proactively, monitoring of borehole operations in realtime is vital on wells drilled today. Realtime monitoring (Pore Pressure while Drilling – PPwD) gives the team the best chance to drill the well safely and efficiently to planned targets. Recent proposals by the United Sates Bureau of Safety and Environmental Enforcement indicate realtime monitoring might soon be mandatory on many offshore US wells. One particularly important aspect of realtime monitoring is pore pressure and fracture gradient estimation and prediction.

Most analysis of drilling data, such as petrophysical, drilling parameters, gas and geology, relies solely on depth-based data, which of course are only available while drilling ahead, i.e. wellbore depth is increasing. The depth-based analysis model is relatively low resolution with data points at 0.5 foot or 0.2 meter intervals. If calibrated correctly the models are valuable and accurate, providing the well team with useful insight about present and possible future events.

However, there are many operations during the drilling of a well that do not generate depth-based data, such as pipe connections, circulating off-bottom, wiper trips, flow-checks etc., that instead, generate time-based data. When analyzed, such data provide invaluable information to permit further calibration of the models. Realtime pore pressure models that only contain depth-based information are potentially flawed because the many calibration points that occur while the bit is off bottom are not captured/recorded in the model. Building a time-based model in parallel to the depth-based model allows for a far more robust picture of downhole conditions.

This paper will use real examples from the Gulf of Mexico to explain the importance and benefits of constructing a time-based model that will be used alongside the depth-based model. It will also demonstrate how discrepancies between depth-based models and time-based models can arise.

The result of using all available data, in both depth and time domain, is a more robust, integrated model on which to base the pore pressure estimation and prediction and ensure the well team gets the best possible information.
Dissolvable Metal vs. Dissolvable Plastic in Downhole Hydraulic Fracturing Applications
Authors: Walton Zachary , Fripp Michael , Merron Matt
Published: April 2016

Multiple dissolvable materials are becoming available in the energy industry. While dissolvable plastics have their applications, a dissolvable metal has distinct advantages over a dissolvable plastic for hydraulic fracturing.

Multiple tests were performed to compare the characteristics of dissolvable metals and dissolvable plastics. The two product families that were explored were dissolvable frac balls and dissolvable frac plugs. For direct comparison, frac balls and frac plugs were constructed using a dissolvable metal and dissolvable plastic. For both dissolvable frac balls, the materials were tested for impact resistance. For both dissolvable frac plugs, the materials were pressure tested.

The dissolvable metal frac ball provided higher impact resistance than the dissolvable plastic frac ball. The dissolvable metal frac ball survived impact at 19 bbl/min on ball-to-seat interference as small as 0.035 in. When the same test was performed using a dissolvable plastic ball, the ball shattered and passed through the seat. The seat overlap needed to be increased to 0.125 in. before the dissolvable plastic ball was able to consistently survive impact against the seat. For the frac plugs, the dissolvable plastic was unable to be used as a bottom slip because of the anchoring loads generated while the plug sealed against differential pressure. The dissolvable metal was able to anchor these loads when used as the material for the bottom slip. For a dissolvable plastic mandrel to survive the setting loads, it had to be set in compression. The dissolvable metal mandrel had no issue being set in tension, allowing for the operational setting procedures to be unchanged. Dissolvable plastic also required the inner diameter of the frac plug to be much smaller.

Using dissolvable metal instead of dissolvable plastic reduces design requirements for converting non-dissolvable downhole tools to dissolvable ones. Dissolvable metal provides an increased impact resistance, has no issues being set under tension, and allows for using smaller ball-to-seat overlaps, all of which provide more flexibility for use in industry applications.
An Evaluation of Subsea Gas Scrubbing at Extreme Pressures
Authors: Setekleiv Eddie , Anfray Jérôme , Boireau Clément , Gyllenhammar Emil , Kolbu Jostein
Published: April 2016

High pressure separation may be needed in subsea compression systems for long distance subsea tie-backs if a dry gas compressor specification is to be met. This paper investigates the performance of gas scrubbers at high pressure (>200 bar). Axial flow cyclones are the last stage of gas polishing within a conventional gas scrubber, and will determine the gas quality. Gas/liquid separation at high pressure is known to be challenging as density difference and surface tension is reduced between hydrocarbon phases. Re-entrainment of liquid droplets in axial flow cyclones is considered a limiting factor for efficient separation at high pressure. Using re-entrainment as a design criterion alone will effectively reduce the gas velocity through the cyclones. Reducing gas velocity to limit re-entrainment can result in poor separation due to a reduction in centrifugal force, causing more droplets to escape the cyclone. In this paper, existing models from literature for re-entrainment and cyclone cut size are extrapolated to field conditions of a notional deep offshore gas field. The goal is to map performance and explore limitations of a conventional scrubber design with axial flow cyclones for subsea high pressure separation. The extensive use of modelling and design rules effectively identifies issues and limitations of existing design approaches for gas scrubbing when moving to higher pressures.
Qualification of New Design of Flexible Pipe Against Singing: Testing at Multiple Scales
Authors: Golliard J. , Lunde K. , Vijlbrief O.
Published: April 2016

Flexible pipes for production of oil and gas typically present a corrugated inner surface. This has been identified as the cause of "singing risers": Flow-Induced Pulsations due to the interaction of sound waves with the shear layers at the small cavities present at each of the multiple corrugations. The new flexible technology discussed in this paper, called K-carcass, is made of shaped wires and presents a very different bore profile compared to other folded-strip flexibles. In a preliminary study based on small scale testing, it was showed that the new inner profile geometry of this technology was more robust for Flow-Induced Pulsations compared to the folded strip carcass. A qualification program was initiated to address the different risks associated with the introduction of a new pipe technology. A primary goals of this qualification program was to extend the results of the preliminary study to the actual carcass at field conditions (natural gas at production pressure).

In this paper, the method followed to qualify the singing behavior of the new flexible technology as installed in the field at operational conditions is considered. The testing program and the scaling approach used to extrapolate results obtained at different scales towards full-scale pipes are described. The program includes a combination of small-scale and large-scale testing. The small scale singing testing consists of blow-through tests of 2" and 3" pipes with corrugated inner bore with air at low pressures on a setup with well-defined acoustic boundary conditions. The large-scale singing testing consists of similar tests on 3" and 5" pipes with natural gas at close-to-operational pressures. These tests are completed with full-scale tests, where a reference riser and a prototype of new-technology riser are tested with natural gas at high pressure. The combination of scales and gas properties at which the tests are done, and the continuity between the different tests conditions, will allow the validation of theoretical and empirical scaling laws used in the qualification of the new riser in operational conditions.

The blow-through tests with the prototype pipe with the new K-carcass tested with natural gas at close-to-operational pressure did not show any singing. In contrast, the reference pipe (with folded-strip carcass) started singing even at low velocities. The test results can be extended to an allowable production envelope for a pipe in field conditions.

Such a qualification of new technology has to rely on existing prediction tools. As these tools were developed to analyze the singing behavior of the existing technologies, this combined theoretical and experimental approach reduces the risks associated with the introduction of a new technology.
Development and Qualification of a Subsea Compressor
Authors: Kleynhans George , Brenne Lars , Kibsgaard Svend , Dentu Pascal
Published: April 2016

Oil and gas production in the Norwegian Sea has been ongoing for decades. The Åsgard B platform produces gas and condensate from the Mikkel and Midgard reservoirs from subsea wellheads with 50 to 80 km long pipeline tie-backs. Because the production started to decline, several innovative technologies were investigated to extend the production and increase the total recovery from the field. Artificial lift, by applying compressors installed on the seabed close to the wellheads, was the most favorable solution. An all-electric hermetically sealed integrated motor-compressor was selected to fulfil this duty and an extensive technology qualification program over 10 years was initiated.

Machine qualification activities included both component and full scale testing levels with the aim to arrive at a low risk subsea compressor solution with utmost robustness and reliability. The component testing level placed major focus on screening available materials to withstand exposure to the raw wellstream fluid from the Åsgard field. Full scale motor compressor testing was performed in a dedicated test facility with hydrocarbon fluids to investigate overall machine performance and enhancement via the introduction of new machine components from the material screening testing.

Valuable operational experience from the qualification efforts were collected and used to establish the design and material selection boundary conditions for the final dedicated subsea compression solution. A particular negative operational experience was fouling induced machine thermodynamic and rotordynamic performance degradation and the need to introduce integrated online washing and machine wet gas compression compatibility to reduce operational risks. To preserve machine robustness and mitigate potential corrosion and erosion problems, a machine concept with unconventional low operating speed and enhanced materials was selected. The world’s first subsea compressor with the above concept attributes was successfully manufactured, tested, installed, and operated subsea at a depth of 260 meters.

The qualified machine has been designed and tested for presence of free liquids such as water, hydrocarbon condensate, and glycol in the gas stream and demonstrated full capability to operate within the complete compressor performance map with liquid content exceeding levels found in normal gas-condensate fields. An available high performance wellstream compressor can reduce the complexity and cost of future subsea compression systems.
Subsea Compression – Project Overview
Authors: Vinterstø Torstein , Birkeland Bjørn , Ramberg Rune Mode , Davies Simon , Hedne Pål Eirik
Published: April 2016

2015 represents an important milestone for Statoil as both the Gullfaks and Åsgard subsea compression projects achieved production start-up.

The Gullfaks subsea wet gas compression system is projected to increase recovery from the Gullfaks South Brent reservoir by 22 million barrels of oil equivalent. The solution involves two 5 megawatt wet gas compressors that handle a production rate of 10 million standard cubic metres of gas per day. The compressor system is connected to existing subsea templates and piping 15 kilometres from Gullfaks C.

The Åsgard subsea compression system is projected to provide 306 million barrels of oil equivalent in increased recovery from the Mikkel and Midgard fields. The solution involves two 11.5 megawatt centrifugal compressors that handle a production rate of 21 million standard cubic metres of gas per day. The compressor system is connected to existing subsea templates and piping 40 kilometres from Åsgard B. The difference in scale and boosting requirements helps to explain why two quite different technical solutions have been selected.

This presentation will provide an overview of the two projects including:

Why subsea compression

The business cases and technology selection

The technology assessment and qualification.

The execution program for the projects including engineering, procurement, construction, testing and installation.

Commissioning and start up

Future subsea compression opportunities
Offshore Chemical Injection Skid for use in Biological Enhanced Oil Recovery BEOR
Authors: Samuel Michael , Nimitz Ken , Gaubert Blane , Swider Chris
Published: April 2016

Offshore enhanced oil recovery (EOR) applications have been historically challenging to implement. A successful EOR program should increase oil production with minimal disruption to operations and to the environment. Proper consideration must be given to the injection equipment footprint, power consumption, and environmental impact of the program.

The proposed technology for improving water flooding can be seamlessly implemented into existing offshore infrastructure. The continuous injection of the tailored nutrient formulation can increase recovery of original oil in place by 9-12%. Mobilization of residual oil occurs from biological activation of subsurface microbes by nutrient introduction, and subsequent growth of the biology.

Mobilization of residual oil, which increases the production rate and recovery, is achieved by activating key populations of microorganisms. These populations, largely dormant, are reactivated and propagated by continuously adding small amounts of highly concentrated nutrients into the injection water stream. The nutrient injection hardware is designed to precisely integrate with existing offshore production infrastructure, limiting the disruption of existing operations, while increasing incremental oil production.

The equipment is composed of an injection skid and a nutrient reservoir. Both have been specifically designed to limit occupied facility space. The bulk nutrient is maximally concentrated to extend time between re-supply of the nutrient reservoir. By design, the bulk nutrient is also biologically degradable once diluted. Two small points of injection introduce the BEOR process into the current waterflood scheme.

This paper describes the mobilization, commissioning and operation of fully automated injection skids with configurations that include aerated, non-aerated, high-pressure, and low-pressure injection. The paper documents operational challenges in controlling nutrient injection rates based on water injection volumetric fluctuations along with operator benefit from remote web based data and alarm monitoring.
Field Development Optimization: A SURF/SPS Alliance Experience and Perspective
Authors: Cormell Darren , de Ligny Florent Hurault , Field Kevin , Lazcano Juan
Published: April 2016

Field development studies performed early in the conceptual stage of a project are an essential process to reduce costs and bring value. The early engagement of an integrated Subsea Production Systems (SPS) and Subsea Umbilicals, Risers, and Flowlines (SURF) combination in this phase brings specific additional benefits to this fundamental element of the development process.

This paper presents the experience and perspective of a SURF/SPS alliance in such field development optimization studies. This new approach is part of a global trend within the industry, in reaction to the current low oil prices and degraded business environment, to cut costs and push the projects towards the threshold that will make them economically viable. Historically, field development optimization has mainly been performed by operators supported by specialized engineering companies. SPS and SURF contractors are now developing and engaging in this activity, offering new vision, optimization ideas and specific technology solutions enabling cost reductions.

The long term alignment of SPS and SURF capabilities delivers a sustainable improvement in Field Development value through a holistic contractor driven approach to overall solutions. General principles of field development optimization are presented, including identification of cost and schedule drivers, the interfaces between SURF and SPS, and CAPEX/OPEX inputs with consideration of how the aligned SURF/SPS capabilities positively influence these drivers.

The key elements of how an aligned approach can bring value through reduced costs and improved schedules, risk mitigation, improved interface management, and more predictable delivery outcomes are presented within the paper. Consideration is given to alternative early engagement approaches, a selection of technical field development optimizations enabled by an integrated SURF/SPS combination and an integrated project execution approach with associated synergies and opportunities described to develop the benefits of an alliance perspective.
Game-Changing Floating LNG Solutions
Authors: Talib Javid H. , Germinder Bob
Published: April 2016

Floating liquefied natural gas (FLNG) solutions are built from matured oil floating production, storage and offloading (FPSO) technology, primarily to monetize stranded offshore hydrocarbon reserves by locating a floating production system at the offshore reservoir location. The wellhead gas is brought from subsea completion systems and manifolds to the topsides of the FLNG vessel for oil/water/gas separation, where needed, and gas pretreatment and liquefaction.

FLNG solutions are also being considered for exporting nearshore gas reserves or gas from an on-land pipeline network by locating the liquefied natural gas (LNG) production facility near the shore. The larger on-land baseload LNG export production plants require significant capital and take four to five years to be brought online. The FLNG concept provides a faster way to build a small-scale to midscale LNG production facility nearshore in protected waters and/or dockside and provides flexibility for progressive project development and variable LNG sales commitment volumes.

Liquefaction production capacity is generally governed by the size of the reservoir, gas availability and the strategy to export LNG (volume). The quality (composition) of feed gas brought onboard will dictate the complexity and cost of the FLNG facility. Raw gas from the wellhead may contain a large amount of liquids and condensate and heavier hydrocarbons (rich gas), while a pipeline gas from the onshore pipeline network may be very lean. The FLNG facilities for processing and liquefying raw gas could be complex and expensive. Lean gas does not require complex systems. However, in both cases, with a simple single mixed refrigerant (SMR) liquefaction technology, the facility can be cost-efficient, faster to build and easier to operate.

Several innovative, low-cost and game-changing FLNG configurations have been conceived based on the space-efficient and simple-to-operate liquefaction technology – PRICO® SMR – for both offshore and nearshore applications. The simplicity, flexibility and scalability of this process allow a wide range of liquefaction capacities in a unique single- or multiple-train configuration. These configurations include new-built carriers and conversion of existing LNG and bulk carriers.

This paper covers the development of innovative FLNG solutions, including all critical systems and other aspects of the technology and their impacts on the configuration of these solutions, offshore or nearshore.
Numerical Maximization of the Secondary Polymer Flooding Value in a Mature, Offshore, Heavy Oil Reservoir
Authors: Mogollón J. L. , Tillero E. , Gutiérrez I. , Luján L.
Published: April 2016

Successfully implementing polymer flooding and maximizing benefits requires selecting best options of variables such as polymer concentration and slug, and number and location of new wells. Option-decisions combined generate thousands of scenarios. Therefore, even using smart algorithm optimizers to efficiently find the maximum of a business objective mathematical function can be a very time-consuming process.

The objective of this article is to demonstrate a methodology to improve the chances of finding the maximum net present value (NPV) solution for planning an offshore polymer-flooding; this includes finding, for example, the minimum injection volume to more easily offshore operations.

The reservoir and economy models included here were automatically coupled with software that encloses a smart numerical algorithm for searching complex maximum/minimum functions. The options of the previously mentioned decision variables were selected to maximize the NPV of the inverted five-spot polymer-flooding project under constrained rig availability. The process was conducted in three stages:

Stage 1: potential value estimation

Stage 2: narrowing options through deterministic numerical simulation

Stage 3: A) numerical optimization of all decision variable options except the drilling sequence; B) numerical optimization of the drilling sequence

 

A total of 379 scenarios were numerically forecasted in just a few months. The best scenario showed three times the NPV of the nonflooding case. Compared to the reference water-flooding scenario (i.e., all the same options but with the fluid injected), the NPV was 1.3 times greater, the water-oil ratio (WOR) was 0.45 times lower, and Np was 1.25 times greater. Unobvious scenarios, such as reducing the yearly drilling rig availability but extending drilling by four years, were revealed. A comparison of the working time for Stage 2 with Stages 3A and 3B showed that the numerical optimization is six times faster per scenario generated.

This study demonstrates that the use of numerical algorithms of polymer flooding yields a significant incremental value over traditional deterministic simulations in a much shorter time frame and with fewer costs compared to previous steps related to building a reservoir model. It is expected to be applicable to all types of enhanced oil recovery (EOR) processes.
New Squall Wind Criteria for the Gulf of Mexico
Authors: Jeans G. , Cooper C. , Yetsko C.
Published: April 2016

This paper presents new squall wind criteria for the Gulf of Mexico. Squalls are responsible for sudden rapid increases in wind speed and changes in wind direction, which can have a major impact upon vessels and offshore structures. These need to be quantified for operability assessments and structural design. Extreme squall wind gusts are estimated from many years of measured hourly maximum wind gusts, from the Continuous Winds dataset of the US National Data Buoy Center (NDBC) archive. Quality control was required to remove some anomalous high gust values. The new analysis supports key findings from a preliminary analysis first published in 2014, with a considerable reduction in uncertainty. The new 10-year return period estimates of squall winds (5 second gust at 10m elevation) are approximately 32 m/s. These exceed the corresponding value specified for a winter storm within API 2MET (27.7m/s). This has potential implications for operating criteria in the Gulf of Mexico.
Comparison of Riser Fatigue Methodologies Based on Measured Motion Data
Authors: Mercan B. , Chandra Y. , Maheshwari H. , Campbell M.
Published: April 2016

In-situ riser structural monitoring has been used by a number of operators and drilling contractors to support drilling operations. The measurements have been used to understand the level of accuracy present in the up-front fatigue analysis and to confirm the integrity of the drilling systems, especially during extreme environmental events. However, the field data analysis requires detailed understanding of drilling riser modeling, loading conditions, operations, sensor characteristics and signal processing. Several methods have been developed to calculate stresses and fatigue damages in the riser using measured motion data. Careful selection of the analysis approach will determine the system configuration and validity of the measured results.

Mode shape matching has been widely used for the data analysis where riser response is dominated by Vortex Induced Vibration (VIV). Another riser fatigue method has been recently developed and is based on analytical transfer functions used to convert measured accelerations into curvature. Another method considers FEA-based transfer functions. Some of these methods perform fatigue calculations in time domain while some others in frequency domain.

Each method exhibits benefits and limitations depending on the characteristics of the measured riser response. Selecting the most appropriate fatigue methodology depends on the riser response and instrumentation system design.

In this paper, three fundamentally different riser fatigue methods utilizing measured motion data are described and compared with each other. The advantages and disadvantages of each approach are evaluated and recommendations are provided for when each method should be considered.
A Review of Coupling Approaches for the Dynamic Analysis of Bottom-Supported Offshore Wind Turbines
Authors: Manuel Lance , Sahasakkul Watsamon , Nguyen Hieu , Sari Ali
Published: April 2016

Offshore wind turbines are designed and analyzed using simulation tools (computer codes) capable of predicting the coupled dynamic loads and responses of integrated turbine and support structure systems. A partially coupled analysis using load exchange is often desirable to meet intellectual property rights interests of disparate design teams and developers of the various components. Of interest is the assessment of the validity of such partially coupled analysis approaches for offshore wind turbine systems with various types of foundations. Computer-aided engineering (CAE) tools—such as the National Renewable Energy Laboratory's (NREL's) open-source FAST software and commercial structural analysis and design software—can use partial or full coupling to simulate loads and motions for utility-scale offshore wind turbines with various support structures. In partially coupled analysis, computed tower-base loads from the aeroelastic simulation tool are fed to structural response simulation tool at a suitable interface; required hydrodynamic and wind loads are introduced as needed on the exposed substructure. In fully coupled analysis, the transfer is two-way—i.e., forces at the interface are intrinsically exchanged between the aeroelastic and structural tools at each time step. It is desirable to compare the loads between alternative partially coupled models that are calibrated against a reference fully coupled case. This paper proposes a framework for the assessment of the validity of partially coupled models in the prediction of short-term and long-term loads and motions associated with large utility-scale bottom-supported offshore wind turbines that might be deployed in offshore wind power development.
Using LIDAR Based Control to Reduce Loads on Floating Wind Turbines and Boost Performance
Authors: Guillemin Fabrice , di Domenico Domenico , Sabiron Guillaume , Averbuch Daniel
Published: April 2016

Offshore wind turbines are being developed worldwide as a large scale source of renewable electricity. However, to accelerate and secure the development in the long term of offshore wind, there is a need to reduce the cost of electricity. To achieve this, wind turbine manufacturers are developing larger size wind turbines, which allow foundation, installation and balance of plant cost reduction. Developing larger wind turbines brings new design challenges, as offshore wind turbines are subject to severe loading resulting mostly from wind speed variation, incoming gusts, and wave loading.

The paper presents current developments aiming at reducing loading experienced by offshore wind turbines using advanced control strategies and LiDAR based long-distance wind measurements.

In order to mitigate the wind loading, modern wind turbines indeed rely on control systems that define optimal blade pitch positions, in order to reduce the load variation, while optimizing produced electricity. However, most control systems are only based on a feedback from the turbine sensors information, and are therefore limited.

In order to overcome this limitation, current developments are being performed to take advantage of additional sensors named LiDAR (Light Detection And Ranging), that can be mounted on the nacelle of wind turbines, and provide long distance wind speed measurements ahead of the wind turbines. Lidars thus provide wind speed measurements at a distance of a few hundred meters, which allow a sufficient reaction time to control the wind turbines.

This paper presents new nonlinear strategies that can be used for bottom founded and floating wind turbines, using  nacelle-based lidar measurement. Examples are given to highlight the benefits of such strategies, on the wind turbines blades and tower fatigue design. Specific strategies are proposed for floating wind applications and exemplified in the paper, showing a significant load reduction for fatigue and extreme situations. Additionally, production increase can also be obtained. Therefore, these two benefits provide an important contribution to cost reduction of offshore turbines.
A Perspective on the Development of a Basis of Design for Evaluation of Seismically-Induced Offshore Geohazards
Authors: Sancio R. , Al-Sharif M.
Published: April 2016

Although numerous studies have been conducted, a recommended practice for incorporation of earthquake loading into the geotechnical design considerations for subsea structures such as wells, manifolds, and PLETs, and pipelines is not consistent. Industry guidance provided in ISO 19901-2 and the more recent API adoption, RP2EQ, provide performance-based recommendations for selection of a two-level seismic design. At the first level the structure is designed to retain its full capacity (and likely its operability) at ground motions with a return period typically under 200 years that depends on the exposure level of the structure. At the second level ground motions that are less likely to occur over the lifetime of the structure are used to ensure global failure is avoided. The guidance, however, was written specifically for fixed steel structures and fixed concrete structures for which exposure incorporates first and foremost life safety, with secondary consideration for environmental exposures caused by system failures, and economic losses to the owners and operator. Subsea field architectures that only include subsea gathering and distribution systems and structures present no exposure to human life, therefore the decision to incorporate earthquake loads should be done with consideration given to mitigation and prevention of environmental releases and tolerable levels of damage. The latter include consideration of: (i) costs associated with production down time and schedule; and (ii) costs for replacement and rehabilitation of damaged facilities.

In this paper we provide: (1) a discussion on existing industry guidance for reliability-based design; (2) reliability-based process for incorporating triggering of seismically-induced soil liquefaction and its consequences into foundation design, and design criteria in a moderately seismic environment with a seabed architecture that only includes manifolds, PLETs, pipelines, umbilicals, and associated structures; and (3) a reliability-based process for evaluation of seismically-induced stability of slopes and its incorporation in the evaluation of pipeline routes.
Seismic Stability Performance of a Coastline Slope Beneath a Pipeline: A Case History of Onshore Observations for Offshore Application
Authors: Sancio R. , Rice A. , Been K. , Villet Willem
Published: April 2016

Under the Pacific Ocean off the south coast of Peru the Nazca tectonic plate subducts beneath the South American plate, creating a high seismic hazard along this coast. Onshore site development and preparation for LNG plant and export terminal construction in this area required a significant volume of excavation throughout the process area and storage area, which are located on a plateau cut to elevation 125 m, separated from the marine loading terminal by coastal cliffs. Steep cuts were incised into the plateau to build a 3.5H:1V sleeper way to allow the LNG cryogenic pipeline system to traverse down the cliff onto a marine jetty to reach the loading terminal. Approximately 230 thousand cubic meters of spoils resulting from the excavation of the sleeper way were pushed over the cliff onto the undercliff area. Additionally, about 630 thousand cubic meters of the stripped material from the process and tank area was pushed over the cliff onto existing colluvial materials in the undercliff. Soon thereafter a crack measuring about 0.3 m in width with a vertical displacement of 0.4 m, and sympathetic cracking occurred sub-parallel to the shoreline at numerous locations across the undercliff area.

A translational mass movement with a volume of approximately 18 million cubic meters was identified following the installation of inclinometers. Regrading of the spoil piles was designed and implemented causing the mass movement to stop. However, simplified and detailed slope stability analyses indicated that seismically-induced permanent slope displacements should be expected during significant earthquake events. A cumulative distribution function (CDF) that incorporated slope parameters and ground motion uncertainty was developed for slope displacements using the Newmark procedure. CDFs were developed conditional to the occurrence of the design earthquake events. Design displacements were selected based on owner risk tolerance and then incorporated into the design of the pipeline through: (a) the installation of a thicker wall at the location where displacements were expected; and (b) installation of an additional extensional loop on the pipeline. Shortly after completion of regrading to stabilize the mass movement, the slope was subjected to an M = 8.0 earthquake that caused permanent slope displacements in the range of 10 to 80 mm across the sliding plane.

This paper describes slope performance from inclinometer and surface movement marker data following the M = 8.0 earthquake, comparison to the results of a probabilistic prediction of seismically-induced permanent slope displacements using simplified procedures, and discussion for the analysis and design of slopes subject to earthquake induced ground motions and incorporation into subsea design basis.
Prediction of Asphaltene Onset Pressure from Dead Oil Stability
Authors: Haghshenas Mehdi , Balashanmugam Soban , Gonzalez Doris , Pietrobon Marney
Published: April 2016

Asphaltene deposition is a major flow assurance issue in some of the deepwater reservoirs in the Gulf of Mexico. Prediction of asphaltene onset pressure (AOP) is essential for the management of the asphaltene threat. Generally, determination of AOP requires pressurized down-hole samples with very low or no oil-based mud contamination. The opportunity to acquire such high quality samples is not always available. This paper presents a novel approach for the prediction of asphaltene onset pressure from dead oil samples based on the asphaltene instability trend method.

The asphaltene instability trend method compares the estimated live oil refractive index and the onset refractive index extrapolated to high pressure/high temperature conditions to infer asphaltene instability. The main laboratory measurements that are used for AOP prediction are refractive indices of oil-precipitant mixtures at the onset of asphaltene precipitation. The asphaltene instability prediction is based on the assumption of a linear relationship between onset refractive index and temperature and also the molar volume of precipitant. In this work, we incorporated the use of equation of state and high pressure / high temperature stock tank oil density measurements to estimate the refractive index of live oil. Also, the molar volume of solution gas was estimated by an equation of state and used to extrapolate the onset refractive index. These modifications minimized the sensitivity of calculations to the lab data and provided more accurate AOP predictions compared to the original method.

The modified approach was applied to several oil samples from the Gulf of Mexico. The estimated AOPs were within 20% of measured AOPs from live oil samples. The new method provides an alternative for asphaltene stability prediction when a high-quality bottom-hole sample for direct measurement is not available or the lab data is inconclusive.
Bridging the Gap Between Design World and Online, Real-Time, Dynamic Simulation World
Authors: Parthasarathy P. , Mai M.
Published: April 2016

The last twenty-five years have seen tremendous growth in the field of flow assurance and real-time flow assurance software for pipeline / asset management. There exists a great divide between dynamic multiphase flow simulations executed during the design phase of a project to that executed during operations in an online environment and this divide is usually not well understood, nor are operators / service providers adequately informed. Some of the key differences are:Design analysis is driven by project design basis and the engineer is in control of the simulations, while online systems are instrument driven and the process is in control.Accuracy is front and center of design simulators while robustness takes a secondary role, but in online systems both accuracy and robustness share equal importance.Design simulators primarily cater to design engineers who are well versed in the software while online systems cater to a more diverse audience, including operators, engineers, and management.

This paper is aimed at providing background on the issues detailed above through real-world examples. Through these examples that have been encountered during the last two decades of developing, installing and maintaining Virtuoso®, we show how real-time modelling can assist in flow assurance of a production system.
The Importance of Soil Characterization in Modelling Sediment Density Flows and Implications in Assessing Infrastructure Interaction
Authors: Ingarfield Samuel , Sfouni-Grigoriadou Mariangela , de Brier Charles , Spinewine Benoit
Published: April 2016

Assessing risk to subsea infrastructure from submarine mass movement events is becoming increasingly important as operators move in to deep-water environments characterized by evidence of prior mass movement activity. An integral part of this assessment is modelling the behavior of potential sediment flows, and their interaction with infrastructure. This paper presents two advanced debris flow models used in industry, and emphasizes the importance of appropriate high quality soils testing when choosing model parameters through an idealized case study, as well as a hypothetical flow simulated on real world bathymetry.
A Risk Based Approach to Managing the Integrity of Aging Production Facilities in the Gulf of Mexico
Authors: Kemp Douglas
Published: April 2016

This paper describes how one company developed and implemented a risk-based integrity management system and applied it to operated facilities within the Gulf of Mexico.

The challenges of maintaining integrity of offshore assets change constantly throughout the life of a facility. The adoption of an Integrity Management System that integrates both risk-based and prescriptive practices can allow an operator to identify changing integrity threats and apply proactive mitigation strategies in good time. Successful use of an IMS can enhance safe operation and regulatory compliance while maintaining up time during declining production.

The paper describes the challenges faced in applying these techniques within the Safety and Environmental Management System regulatory regime and Gulf of Mexico operating culture and reviews Lessons Learned in developing and implementing the Integrity Management Systems

The paper describes how the IMS facilitated the assessment of platform condition and remaining life and how this in turn influenced the remediation requirements and subsequent maintenance and integrity activities required to facilitate life extension.