bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and Mechanical Properties of a Fine-Grained AZ91 Magnesium Alloy Prepared by Multi-Pass Friction Stir Processing
Authors: Lu Zhi Long , Zhang Da Tong
Published: March 2016

Friction stir processing (FSP) is a novel severe plastic deformation technique developed in recent years to produce fine-grained structural materials. Through increasing the processing pass, further grain refinement can be achieved. In this paper, the microstructure and mechanical properties of AZ91 magnesium alloy prepared by the single-pass and two-pass FSP were studied. The results showed that the coarse, network-like eutectic β-Mg17Al12 phase was broken into particles and some of them dissolved into the magnesium matrix, and the α-Mg grains were remarkably refined after FSP. The average grain sizes of the single-pass and two-pass FSP alloys were 8.3 μm and 5.8 μm respectively. The ultimate tensile strengths of the specimens were 284.5 MPa and 319.7 MPa, and elongations were 13% and 14.5%, respectively. The improved mechanical properties of the two-pass FSP specimen were mainly attributed to the finer grain size and more homogenized microstructure.
Effect of Aging Treatment Technology on Properties of Al-Mg-Si-Cu-Zr-Er Alloy for Auto Sheets
Authors: Zhao Qian , Yuan Xiao Guang , Huang Hong Jun , Zhao Peng
Published: March 2016

The effect of natural aging, pre-aging and paint-bake aging technology on properties of Al-Mg-Si-Cu-Zr-Er alloy for auto sheets was investigated by performance testing, microstructure observation, and differential thermal analysis. The results showed that the natural aging alloy before and after paint-bake aging presented the double peaks feature of both the mechanical properties and hardness, the maximum value of strength and hardness appeared on the second aging peak, and the paint-bake aging softening occurred. The result of differential thermal analysis showed that, compared with the artificial aging, the precipitation of β′′ phase was delayed after the natural aging; the precipitates were mainly β′′ nuclei at the paint-bake aging, and it is difficult to achieve paint-bake aging hardening. After pre-aging and nature aging treatment, the precipitates were mainly composed of β′′ phase at the paint-bake aging, and the paint-bake aging hardening was realized. The addition of Er and Zr elements accelerated the precipitation of β′′ phase, the precipitation temperature of β′′ phase reduced and the time of the first natural aging peak and pre-aging was shortened. The parameters of pre-aging treatment of alloy sheets was solution and water quenching, and then age at 170 °C for 5 min.
Stress Analysis for the Tie-in Girth Weld of X90 Pipeline
Authors: Zhou Yan , Fan Yu Ran , Yao Deng Zun , Zhong Ting , Zhang Xi Xi
Published: March 2016

Tie-in is a very important step on the final stage of pipe construction. The stress of the tie-in girth weld is really one of the key roles that affect the security of the pipeline in service. In this paper, Finite Element Method (FEM) was used to determine the stress of the tie-in girth weld. The factors of stress of tie-in girth weld were analyzed. The results show that uncovered pipe length, tie-in offset and misalignment were the important factors which affect the stress of tie-in girth weld. The maximum Mises stress and axial stress at tie-in girth weld increased with the uncovered pipe length decreasing and the tie-in offset increasing. The stress also increased significantly with girth weld misalignment, especially for axial stress.
Short-Term Creep Behavior in P91 Heat-Resistant Steel at Low Stress
Authors: Zhao Peng Shuo , Shen Jun Jie , Zhang Hui
Published: March 2016

P91 heat-resistant steel is widely used in the high temperature of piping components of thermal power plants and nuclear power plants. In these conditions, the typical failure of P91 is mainly caused by creep at low stress. In this investigation the short-term creep behavior in P91 at low stress was investigated by helicoid spring creep test due to its high strain-sensitivity. The helicoid spring creep was based on the assumption of pure torsion. The mechanics field was firstly studied by ANSYS finite-element simulation to find the establishing conditions of pure torsion. Secondly, the creep properties of P91 were studied under the conditions of the temperatures of 0.38Tm<T<0.46Tm and the stresses of 14.6 MPa, 25 MPa, 34 MPa, respectively. The ANSYS finite-element simulation shows that the creep deformation is considered to be pure torsion when the pitch spacing of coil is between 2mm to 4mm. The creep curves show "Normal type ", and “the stress exponent” is n=0.9.
Magnetic Shape Memory Alloys Modelling and Pneumatic Applications
Authors: Flaga Stanisław , Nowak Amadeusz , Stefański Frederik , Minorowicz Bartosz
Published: March 2016

Very generally material science could be divided into two groups: scientists who try to invent new materials or improve existing ones and those who work on finding the best applications for the modern materials. Among them there is group named “smart materials” or “active materials”, which have ability to change theirs properties according to the external stimulation. One of the relatively most recent smart material is magnetic shape memory alloy, MSMA in abbreviation. The authors of the article focus on testing samples of this material and try to adapt them to use in fluid devices. The paper mentions about some most interesting valves’ designs equipped with smart materials and summaries the previous MSMA research of the authors. It begins with literature overview of smart material applications in pneumatic or hydraulic valves. There is only one example of MSMA application in valve, therefore the overview concerns mainly the use of piezoelectric, thermal shape memory alloys and giant magnetostrictive materials. Next section describes general properties of the magnetic shape memory alloys and underlines the differences between more widely known Thermal Shape Memory Alloys and MSMA materials. One of the most important property is wide, nonsymmetrical hysteresis in static characteristics of the material, which can be seen as advantage or disadvantage, depending on the application. The material preserves its shape until perpendicular magnetic field or additional force appear. The authors mention about modeling MSMA hysteresis aspect. Three different hysteresis models were briefly described: Generalized Prandtl-Ischlinski, Preisach and Krasnosel'skii-Pokrovskii. The last section treats about the current MSMA based valve design concept. It assumes usage of two identical pieces of MSMA materials and energize them oppositely. There is flapper mounted between MSMA samples, which displacement depends on the MSMA elongations. This actuator type is called “push-push” type. Lack of the return spring result in remaining of the flapper in its final position after decreasing of the supply current. The advantage of the solution could be lowering energy consumption of the valve, when the valve setting changes relatively rare during its work. In the future, the presented hysteresis models could improve the work of such MSMA based valve.
Novel Lightweight Biopolymer Drilling Fluid for Underbalanced Drilling
Authors: Nee Lim Symm , Khalil Munawar , Jan Badrul Mohamed , Ali Brahim Si
Published: March 2016

This research centres on optimizing the formulation of a water-based lightweight biopolymer drilling fluid using Design Expert for underbalanced drilling (UBD). Response Surface Methodology (RSM) was selected as a viable means to obtain the optimized drilling fluid formulation. Concentrations of four main raw materials (glass bubbles, clay, xanthan gum and starch) were varied in a suitable range to obtain the formulation with the desirable density, plastic viscosity (PV) and yield point (YP) for UBD application. Based on the results, the optimized drilling fluid can be formulated with 24.46% w/v of glass bubbles, 0.63% w/v of clay, 0.21% w/v of xanthan gum and 2.41% w/v of starch. The desirability factor, d for this optimum condition selected is 0.628. The mathematical models generated by RSM were able to predict the three response parameters well, as the experimental values were found to be in good agreement with the predicted values. The error is less than 1.0, standard deviation less than 0.5 and the accuracy is more than 98.5%. All mathematical models were quadratic in nature. The model used to predict the PV has an inverse square root transform. This drilling fluid is considered to be less harmful to the environment as it is water-based and, at the same time, composed of natural polymers (xanthan gum and starch) which are biodegradable. With this novel formulation, we could expect to drill more wells in underbalanced conditions to improve production of oil.
Case Study: Integrated Strategy Solves Well Test Issues in Deep-Water and Heavy-Oil Environments
Authors: Zhong Cheng , Liang Zhang , Zhengli Liu , Junbin Zhang , Yuezeng Wang , Kun Cheng
Published: March 2016

As the operator, CNOOC completed drilling two exploratory wells in a deep-water field of the Republic of Congo from May to November of 2013, in 600 m of water depth. Indications of oil and gas- heavy oil layer, gas layer and thin oil layer were found in the E-1 well according to logging data analysis. There are many challenges for the operator and service companies to perform the appraisal of this heavy oil reserve in a deep-water offshore environment, such as operational cost control, low temperature near the seafloor/mud line, heavy oil flow assurance, sand control, etc. In order for the well test to be effective, all the above issues must be fully understood and methodology employed that will reduce the chance that operational risks will occur.

This paper presents an integrated well test program of the E-1 well developed and implemented for reservoir characterization and formation evaluation in the Congo basin. The program used a combination of various formation evaluation techniques such as wire wrapped screen sand control, PCP with electric heating rod and insulation tubing, hydrate prevention, emergency response in complex condition. The integrated well test program was designed and modified to meet the project delivery timeline and cost constraints, while responding to the challenge of properly testing the oil/gas reservoirs.

This paper also gives the data analysis results and summarizes the encountered problems and learned lessons from field operations.

The treatment practices and gained experiences from the field operation presented here provide valuable guidance for future deep-water heavy oil exploration and development operations.
Integrated Wellbore Suveillance Techniques for Effective Reservoir Management Plan
Authors: Saadat Aliasghar , Rahman M. Redzuan A. , Masoudi Rahim , Salim Sharina M. , Othman Mohamad , Shnaib Fathi Younis , Karantharath Radhakrishnan
Published: March 2016

Production optimization and improved recovery efficiency while reducing operating and capital expenditure has been the main goal of the operators, and makes it imperative under the current oil prices. Reservoir Management Programme (RMP) is a comprehensive and integrated process of establishing control over hydrocarbons appraisal, extraction, voidage replacement, and optimizing production and reservoir performance, and it is the key to achieving maximum recovery. Monitoring well and reservoir performance from initial completion to abandonment is critical to ensure efficient operation, optimum economics, and safe environment. Tracking production rates, water cut, wellhead pressure, casing pressure, well integrity, and planning recompletion, workovers, sidetracks, in-fill drilling, enhanced oil recovery etc. will require close watch, accurate analysis, and timely execution at considerable cost and effort. Therefore, it is critical to stay up-to-date on the latest developments in technological advancements in this area, be judicious in the methods used in acquiring the right data at the right time, and more importantly, integrating all acquired data to discern performance patterns, predict future behavior, and avert any problems. More detailed understanding of reservoir characterization and reservoir physics are the need of the hour to be efficient and successful in the various stages of the exploitation of the reservoir.

Furthermore, advances in horizontal drilling, smart well completions, deep-sea drilling, and highly complex operation, have changed the playing field and rendered many old conventional tools inadequate to meet the new challenges. For example, rates from some intervals along a horizontal well can be too low to be measured by a typical flowmeter. The cost of measuring reservoir pressure in individual layers can be cost prohibitive, especially once the completion is in place. Reservoir characterization, understanding lateral continuity, and permeability anisotropy can be time consuming and expensive. Locating the source of a casing pressure accurately, quickly, and without having to mobilize special equipment (rig-less) is critical.

This paper illustrates the application of the above principles by showing actual cases, methodology of data acquisition and processing, focusing on the added value from the new information.
Prediction of Drag Anchor Trajectory With Both Shallow and Deep Anchor Behavior
Authors: Wu X , Chow Y. K. , Leung C. F
Published: March 2016

The uncertainty of drag anchor installation behavior is still an issue for drag anchor design. The existing method applying yield envelope for the anchor kinematic analysis ignored the shallow anchor behavior. Finite element analysis is conducted to study the shallow and deep anchor behavior under combined loading, which are characterized by yield envelopes for the kinematic analysis of anchor installation behavior. The impact of yield envelopes and shallow anchor behavior on the anchor kinematic performance is investigated. It is found that the largest difference in the predicted results such as anchor embedment depth using existing yield envelopes based on deep anchor behavior alone is about 43%. When shallow anchor behavior is considered, significant difference is shown. The predicted embedment depth taking account of shallow anchor behavior is shallower than that using only yield envelope for deep anchor behavior. The kinematic parameters are significantly influenced by the shallow anchor behavior. The current research improves the application of the yield envelope approach for drag anchor design and considers the influence of shallow anchor as well as deep anchor behavior on the anchor kinematic performance.
Six Years On: How the Global Industry has Risen to the Oil Spill Response Challenge
Authors: Flynn Steven A
Published: March 2016

The April 2010 Gulf of Mexico oil spill (Macondo), and the earlier Montara incident in Australia, prompted the entire industry to re-examine both the operational aspects of offshore activities, and their preparedness for an oil spill or well blowout.

To meet this challenge, the International Association of Oil and Gas Producers (IOGP) formed the Global Industry Response Group to translate the learning from the incident and subsequent response, into practical recommendations for the future. The oil and gas industry's international environmental association - IPIECA - managed the joint industry project (JIP) to progress the nineteen recommendations on emergency management and oil spill preparedness. Discreet projects were initiated, or other trade associations’ projects supported, to deliver a series of practical guidelines, tools and techniques for the industry.

This paper reviews the products from Phase I of the project and how they are changing the way that organisations plan for, and respond to, incidents. Progress on Phase II, which started in 2015, will also be presented, concentrating on incident management, oiled wildlife response, and satellite remote sensing technology for identifying and tracking spills.

The Joint Industry Project is comprehensively revising the way industry prepares for emergency response and has made several new techniques available. These range from methodologies such a Net Environmental Benefit Analysis (NEBA), through response technologies such as In-Situ Burning and Sub-Sea Dispersant Injection, to comprehensive emergency management tools such as the Common Operating Environment.
Design Considerations for Mitigating the Impact of Contaminants in Rich MEG on Monoethylene Glycol Recovery Unit MRU Performance
Authors: Latta T. M. , Palejwala A. A. , Tipson S. K. , Haigh N. P.
Published: March 2016

Supplying monoethylene glycol (MEG) to the wellhead is critical to gas production since interruption of MEG injection can lead to loss of well production due to the risk of hydrate plug formation in the subsea production infrastructure. Maintaining a high reliability of MEG supply is heavily dependent on good MEG Recovery Unit (MRU) performance.

This paper is applicable to subsea gas-condensate wells using MEG for hydrate inhibition and outlines a holistic approach towards diminishing the impact of contaminants in Rich MEG on MRU operating performance. An overview of the impact of various contaminants on MRU operation and how to deal with them will be discussed. Conceptual design considerations and practical applications as per vendor experience will be presented, as well as, examples of the impact of Rich MEG contaminants on MRU operation.

During the life of the gas reservoir, both short term events (e.g., completions fluid clean up, well start up, flow rate increases) and long term events (e.g., hydrocarbons entrainment, clay, silt, corrosion products, corrosion inhibitors, scale inhibitors, demulsifiers, formation water breakthrough) introduce contaminants into the Rich MEG that need to be considered in terms of impact on operational reliability of the MRU. If the effects of the contaminants result in reducing the reliability of the MRU to less than the desired design target, then they need to be removed or at least reduced in quantity to a level that permits the reliability target to be achieved.

Key groups that need to be involved in conjunction with the Client to ensure successful MRU design are Flow Assurance (wellhead chemistry and pipeline flow), Testing/Simulation facility and/or Vendor facility (study work, bench tests, and/or separation equipment piloting), Hydrocarbons Process Engineering (topsides or onshore processing facilities/MEG Regenerator and MEG Reclaimer design), and the MRU package vendor. Effective communication and collaboration between all parties in the early phases of the project is essential for managing these contaminants and maximizing MRU availability.
Geo-Mechanical Weakening of Limestone Due to Supercritical CO2 Injection
Authors: Zhang Yihuai , Sarmadivaleh Mohammad , Lebedev Maxim , Barifcani Ahmed , Rezaee Reza , Testamantia Nadia , Iglauer Stefan
Published: March 2016

CO2 injection into limestone reservoirs is a typical process in enhanced oil recovery operations, and it is also suggested for carbon geo-storage. However, CO2, together with water, is acidic and creates medium strength acid (pH value 3-4) at HP/HT (High Pressure/High Temperature) conditions. At the same time, it is well known that carbonates react and dissolve when exposed to acid. It can, therefore, be expected that the limestone properties change significantly during CO2 injection.

We thus hypothesized that limestone dissolution results in a substantial reduction of mechanical strength of the rock, with potential subsequent (mechanical) collapse of the rock – which would represent a major geohazard and could lead to land subsidence. We therefore conducted HP/HT core flooding tests on Savonnières limestone plugs; the plugs were thoroughly characterised with various experimental techniques (NMR-T2 response, porosity, dynamic permeability, acoustic response, x-ray computed tomography and rock-mechanical tests) before and after acid injection, i.e. exposure to supercritical CO2.

We indeed measured a significant dissolution of the rock and associated substantial mechanical weakening of the rock. Differently shaped wormholes formed, which strongly influenced the mechanical behaviour. Furthermore, a significant permeability increase was observed (up to 42.3% increase after injection), consistent with wormhole formation. We conclude that CO2 injection may pose a geohazard if the geo-mechanical strength of the reservoir is compromised.
AVO and Spectral Crossplot: A Case Study in the Malay Basin
Authors: Liu C. , Ghosh D. P.
Published: March 2016

Amplitude Varies with Offset (AVO) has been proven to be a useful technique in hydrocarbon exploration in many basins, including Malay Basin. The rocks in this younger Tertiary basin are generally soft, unconsolidated and are sensitive to fluid replacement and response as per Gassmann. Hence, quantitative AVO plays a significant role in hydrocarbon prediction (Ghosh et al., 2014). It was found that the vast majority (70%) of pay zone have Class II AVO types in the Peninsular Malay basin. However, wet sands also can give Class II AVO response in some cases, which causes ambiguous results.

In order to obtain more accurate results, we use spectra cross plot technique which combines AVO and spectral decomposition. This technique is a quick and useful way to discrimination between gas and wet sands (Ren et al. 2007). This study attempts to apply spectral cross plot technique in a field of Malay basin to improve the performance of AVO.
Deep Sea Laser Raman – Past, Present and Future Developments for In Situ Chemical Analysis and Applications
Authors: Kirkwood William J.
Published: March 2016

The Deep Ocean Raman In Situ Spectrometers (DORISS instruments) where developed at the Monterey Bay Aquarium Research Institute (MBARI) for the purposes of identifying compounds and studying in situ chemical reactions in a non-destructive manner while working with solids, liquids and gases. The approach taken began with modification of a standard bench top lab unit for use at sea to demonstrate feasibility. The second generation then solved several impediments to improved performance in the deep sea as well as development of additional tools to enhance capabilities. The third generation is now past the design process and in assembly for bench top testing to bring the fluorescence signal (noise) down to achieve a 19 fold increase in sensitivity. This allows the use of Raman on compounds that have high order organic compounds such as some oils and makes the detection of CO2 much easier. The high power approach in this system will enable faster operations for subsea mining.

The first instrument (DORISS I) was greatly successful and perform science experiments from Canadian waters to the Gulf of California looking at hydrates as well as higher order compounds, gas vents, phase boundaries and the ice cage structures entrapping methane as well as other gases. DORISS I was able to determine thermogenic versus biogenic methane for example. DORISS II increased sensitivity and performance by reducing the pressure effects on the optical system. Precision pointing devices were incorporated to look below the surface of some compounds as well as vertical and horizontal scanning of in situ chemical processes. A pore water probe was developed which allowed for very precise vertical profiling of sediments showing to properly access the methane content in the ocean bottom sediments which in general is greatly underestimated using tube cores and other sampling methods with shipboard analysis. The next generation DORISS, currently in development, promises to give gains in sensitivity as well as the ability to obtain Raman signatures from volatile compounds which would normally be unclassified due to fluorescence.

The application of Raman has revolutionized the medical industry and promises to do the same for oil & gas as well as subsea mining. With the trends in land based Raman spectrometers toward lower costs it can be argued that these techniques enable industry to employ a new tool and manage ocean resources more wisely.
Sensitivity of Smoothed-Particle Hydrodynamic Parameters on Slamming Simulations
Authors: Sasson Marcus , Chai Shuhong , Rafieshahraki Jalal , Jin Yuting
Published: March 2016

The oil and gas industry requires complex subsea infrastructure in order to develop offshore oil and gas fields. Upon installation, these components may encounter high slamming loads, stemming from impact with the water surface. This paper utilises Smoothed Particle Hydrodynamics to quantify these loads on a free-falling object. The investigation is interested in conducting a parameter study and determining the effect of varying simulation parameters on the prediction of slamming event kinematics and forces. The surface impact of a 2D freefalling wedge was simulated, with the results being compared to an experimental investigation. It was found through the parameters that particle resolution and the size of the SPH particle kernel are very important, whilst the diffusion terms do not play an important role. The latter is due to the very transient nature of slamming events, which do not allow sufficient time for diffusion in the domain. The close correlation of numerical and experimental results, along with the robustness and quick set up of SPH slamming simulations, indicate that SPH is a promising method of modelling more complicated slamming problems, which may involve more intricate impacting structures.
Structural Corrosion Modeling for Strength Assessment of Fixed Offshore Platforms for Life Extension Study
Authors: Sari Ali , Ramana Ekkirala , Nguyen Hieu , Arablouei Amir , Azimov Umid
Published: March 2016

The response of a fixed offshore platform subjected to extreme wind and wave loadings (lateral loads) under corrosion conditions is studied. The advanced simulation techniques to model corrosion damage and to perform nonlinear pushover analysis is outlined. The locations of corrosion perforations and thickness reductions can be identified based on an inspection report. A finite element model of the jacket is developed with a focus on these critical locations. The corrosion perforations can be represented as certain analytical shapes, for example, elliptical openings, at different locations, and sizes. The thickness reductions due to corrosion can be approximately modeled as shell elements with varying thickness. The platform capacity under extreme environmental loading is characterized in terms of the platform's Reserve Strength Ratio (RSR). Thus, a non-linear pushover analysis is performed to assess the strength of the corroded structure by quantifying the Reserve Strength Ratio (RSR) value. The nonlinear pushover analysis is carried out using the general finite element package Abaqus.
Remediation of Well Impaired by Complex Organic Deposits Embedded with Naphthenate and Contaminated with Inorganics
Authors: Mohamed Anwarudin Saidu , Alian Sima Sheykh , Singh Jasvinder , Singh Rajindar , Goyal Arvindkumar , Munainni Gurunathan
Published: March 2016

Mature oil wells with high water cut suffer from solids deposition with an agglomeration of species like asphaltenes, wax, resin, metal naphthenates, inorganic scale and formation fines etc. Such solids generally accumulate around the well bore, in the production tubing and surface facilities. These deposits can also change the formation wettability towards oil wet. Solid deposition and wettability change create additional resistance to flow in producing wells leading to decline in rate of oil production. Generally in such cases the production decline can be very steep.

Analysis of some deposit samples from such producing wells in Malaysia shows the presence of macro and micro-crystalline waxes, asphaltenes, resins, metal naphthenates, inorganic scale, sand, silt, clay etc. in varying concentrations. The presence of naphthenate deposits is a new problem in many oil wells. The deposition of naphthenates along with other organic and inorganic components create skin and a restriction to flow. This complex gamut of such deposits, especially naphthenates does not dissolve/disperse completely with solvent followed by conventional acid treatment. This often results in acid induced sludges. Use of solvents, acid blends and other composite fluids is reported to remediate such problems with varying degree of success.

To address the deposit problems induced by naphthenates, an effective micro-emulsion consisting of solvents, surfactants, and inhibited acid etc. has been developed to effectively remove organics. The objective of such treatment is to provide dissolution/dispersion of organics that leads to deeper penetration into near wellbore with no sludge formation.

This paper presents laboratory and field data on a treated well from Sarawak which showed significant enhancement in oil production. The well was completed with a gravel screen and exhibited very low productivity from its initial production due to combined completion skin and formation damage. Significant increase of the production rate (from average of 50 bopd to 900 bopd) was observed after the treatment.
Critical Review of the Existing Liquid Loading Prediction Models for Vertical Gas Wells
Authors: Jafarov Tural , Alnuaim Sami
Published: March 2016

Producing gas wells faces with the challenge of liquid loading mostly in later stages of production. Due to formation of liquid coloumn in the wellbore, the rate decreases below the critical rate. Hence, water reduces well performance. Depending on the wells, liquid coloumn can form because of either entrance of formation water to the wellbore in dry gas wells or wet gas liquidification in wet gas wells or condensation in gas-condensate wells. In all the cases, as a result, bottomhole pressure increases and reservoir pressure does not have enough pressure to force the liquid to the surface. This leads to considerable reduction of well production and that may lead into seizure flow in more severe cases. In last decades, different techniques and correlations have been offered by many authors for determination of critical liquid loading rate. This paper reviews the existing several widely used liquid loading models and highlights their advantages and drawbacks. Additionally, at the end of the paper, a case study has been conducted for these models to identify their applicability conditions and limitations regarding the selection of best matched based on well data. According to the case study's results, Guo's model predicts critical flow rate more accurately than all other models. There's no any applicability ranges, which it can be applied to all vertical gas wells with different wellhead pressures. When it comes to the other models, their applicability ranges should be taken into account carefully for not to ending with incorrect estimations.
Neural Network Based Adaptive Control for a Thruster Assisted Mooring Vessel in Mooring Line Failure
Authors: Kwon H. , Kim N.
Published: March 2016

Classification society standard requires redundancy in floating vessels with thruster assisted mooring system, but it is not avoidable for floating vessels to drive off in an instant of a mooring line failure such as line breakage or dragging of anchor. Such a failure might cause serious hazard by consequent mooring line breakages. Agile response of assisted thrusters in case of mooring line failure is essential to minimize excursion and prevent consequent hazard. Conventional controller based on the moored vessel's intact dynamics is not proper to handle the configuration and dynamic characteristic changed by a failure and it might cause time delay to be stable and recover the vessel's position. This paper presents a neural network based adaptive control method that guarantees stable control performance even with mooring line failure. Neural network based adaptive control can achieve control objectives in the presence of modeling uncertainty. The advantage of the proposed control method is that the controller does not require dynamical model of failure condition. In the case of mooring line failure, the neural network regards configuration change as added modeling uncertainty. Numerical simulations of a semi-submersible type vessel were performed for the validation. Proposed method has robust control performance in the presence of a failure. The results show that the neural network based adaptive control method enables a vessel to response timely and recover the position effectively.
Data Integration and Reservoir Characterization to Understand Water Movement during Production in a Mature Gas Field, Luconia Province, Malaysia
Authors: Chiew Edwin , Warrlich Georg M. D. , Binda Andrea , Adams Erwin W.
Published: March 2016

Interdisciplinary data integration is key to top-quartile Well Reservoir Field Management (WRFM). In our field case, results from annual well-intervention activities were analyzed and integrated with production data and the regional-to-reservoir scale geological understanding of this carbonate gas field to improve the delineation of the gas-water contact (GWC) development and allow timely water shut off (WSO) at the optimal depths in the reservoir, while at the same time utilizing reservoir heterogeneities (such as horizontal baffles) to delay water breakthrough (WBT).

The carbonate gas field is located in Central Luconia, with over 30 years of production history. Some wells have seen significant WBT and the field experiences an uneven rise of the GWC with production. To improve the GWC prediction, reservoir characterization work was aimed to capture the key heterogeneities that matter for flow: baffles vs. high-permeability conduits to water movement. As such, geological characterization focused on low-porosity zone correlation and platform margin & slope deposit interpretation along the flanks of the field, respectively.

In order to understand the baffling nature of rock facies to fluid flow, low porosity zones were mapped across the field initially on seismic and well logs. In core, two types of low-porosity layers were observed: flooding- and exposure-related low-porosity layers. Both types of low-porosity layers show similar log signatures, but behave very differently during production (Warrlich et al., 2014). Flooding-related low-porosity layers are extensive and composed of fine-grained, argillaceous material. They form baffles that are capable of delaying water rise for several years. Exposure-related low-porosity layers, on the other hand, are composed of cemented, brittle limestones and are often associated with karsts and fractures. Their baffling capacity is limited and can even act as high-permeability conduits speeding up the GWC rise, when connected to karst dissolution.

Platform margin and depositional-slope deposits were observed on seismic in the flanks of the field. These are inclined beds of potentially permeable deposits that have been shed from the carbonate platform during sea-level highstands. Commonly the strongest progradation and best-developed slope deposits are located on the leeward side, i.e. platform-top shedding and transport in the main paleo-current direction. Due to their inclined nature, they dip directly into the water leg and thus can act as conduits for water during production.
Optimum Design of Multi-Body Floating Logistics Terminal
Authors: Wada R. , Mondal R. , Kamizawa K. , Takagi K.
Published: March 2016

In the present study, concept of a floating logistic terminal (FLT) is evolved using three floats. Emphasis is given on the best configuration of the structures and the reduction of motion of the floating terminal. We present the preliminary numerical and experimental studies of response amplitude operator (RAO) for heave, roll and pitch. The analysis is executed for three different configurations of the floating structures. Though, the application area is for shallow water, however the deep water case is also studied. The motion characteristics are studied for head waves as well as oblique waves. The results obtained from two different methods are compared.
Permanent Mooring Anchors for Floating Facilities - A Review and Selection Process for Carbonate Soils
Authors: Kennedy J. , Maconochie A. J
Published: March 2016

The use of conventional catenary moorings provide a viable and cost effective anchoring system for the large FLNG field developments proposed along the deeper water regions offshore the North Western coast of Australia. The design of the catenary mooring systems and the anchors are highly dependent on the water depth and the seabed soil conditions. However, the extreme environmental loads associated with these deep water developments dominate the mooring anchor design with anchors required to sustain significant vertical and horizontal loads. Selection of an appropriate anchor design therefore becomes an intensive exercise involving many disciplines including geotechnical, structural and installation engineering to ensure the appropriate and optimum anchor type is selected.

Due to the size and weight of some conventional anchor designs e.g. driven piles, suction anchors etc., over the last 10 years, a number of new anchor concepts have been proposed and developed including DEPLAs, SEPLAs, VLAs, Torpedo piles etc. to improve anchor installability and reduce costs. However, when considering extreme FLNG mooring loads technical challenges and uncertainties still remain for several of these concepts.

Further considerable complexity is added to the anchor design and selection process given the wide range and nature of the seabed soils encountered in the North Western shelf which typically comprise carbonate soils.

A methodical anchor concept screening process has been developed in this paper to review and rate various mooring anchor concepts for FLNG developments, although the process can also be applied to alternative floating facilities and mooring systems such as FPSO developments. The process considers geotechnical, structural and installation drivers that impact on the design to determine the most practical and technically viable solution for the water depth, design loads and soil conditions. As part of a mooring anchor project the results of the screening process can be presented at an early stage in the mooring anchor design for discussion and can act as a starting point to identify the major risks, help optimize the anchor design and highlight areas that require further analyses and testing.
Optimizing Additional Stabilization Requirements of an Existing Pipeline
Authors: Teh Thiam Chuan , Nitchov Tony , Selvam Rajendran , Panambur Sandeep , Mahmoud Abdel Hakim , Qazi Muhammad , Tjahyono Sindhu , Dai Keyang
Published: March 2016

In order to increase oil production, an oil field operator undertook a field expansion program which required the construction of additional satellite platforms and several new artificial islands as centres for future drilling and oil production facilities. As a result of these newly constructed islands, wave and current conditions within the surrounds became more severe. Some sections of the existing pipelines in the vicinity of the new artificial islands were identified to no longer satisfy DNV-RP-F109 Generalized Method's stability criterion of pipe lateral displacement for less than ten (10) times the diameter. This resulted in the need to employ additional stabilization measures for these affected sections. As a consequence of the high costs associated with these measures and the inherent conservatism in the use of small allowable displacements as a failure criterion, a dynamic analysis using finite element method was used to assess the pipeline displacement and the structural integrity responses during a storm duration. This paper details the use of such dynamic analysis to optimize the additional stabilization requirements for one of the pipelines in the field. The results demonstrate that significant cost savings for the operator could be achieved using this method.
Assessment of Nonlinear Roll Damping and Hydrodynamic Loads on Extended Bilge Keels for FPSO/FLNG
Authors: Kim Sungeun (Peter) , Seah Robert
Published: March 2016

Bilge keels are commonly installed on commercial ships and FPSO/FLNG units to effectively mitigate roll motions. Accurate predictions of the roll damping and hydrodynamic loads are critical for the structural design of the bilge keels. In this paper, model tests and Computational Fluid Dynamics (CFD) are employed to investigate the nonlinear roll damping and hydrodynamic loads on the bilge keels. Roll decay tests and CFD simulations are carried out for a FPSO vessel to estimate the roll damping and drag coefficients of the bilge keels with extended depths. Also seakeeping model tests and CFD simulations are carried out to estimate the hydrodynamic loads on the bilge keels in regular beam waves. From this study, it is found that the drag coefficients of the Ikeda formula (1976) and Sarpkaya & O'Keefe (1996), originally developed for wall-bounded plates, can substantially under-predict the drag loads on the bilge keels attached to a FPSO vessel without considering a velocity increment factor. This paper presents the first part of the Joint Development Project (JDP) between ABS and Chevron to develop the procedures for the strength and fatigue assessment of bilge keels for FPSO/FLNG units.
Infinite Conductivity Horizontal Borehole Assumption: Applicability & Quantification of Error
Authors: Abo El Seoud M. A. , Alnuaim S. A. , Shoukry A. E.
Published: March 2016

Horizontal drilling technology is advancing rapidly day after day. That is due to the much higher productivity of horizontal wells relative to vertical wells. However, the paycheck of drilling a horizontal well is also higher. Therefore, the productivity of a horizontal well not just needs to be estimated whatsoever, but the estimation has to be reliable enough. As a faulty-estimated productivity shall result in a faulty economic feasibility of drilling this well, and may cause huge economic losses.

Several types of models discussed the productivity of horizontal wells. Analytical models (ex. Furui) are the most common to use because they are easy to use. Nevertheless, this easiness comes at the expense of the infinite borehole conductivity assumption, which does not account for any pressure drop along the lateral length of the well. This assumption causes severe errors in some situations. On the other hand, semi-analytical models (ex. M. Tabatabaei and A. Ghalambor) couple reservoir inflow with wellbore outflow to estimate the productivity of horizontal wells.

This paper concentrates on showing the value of production rate error resulting from using Furui's model applied on published data of three wells, the error in rate is calculated based on the M. Tabatabaei and A. Ghalambor's model which is assumed to yield the right rate. First, a MATLAB code was developed to implement the M. Tabatabaei and A. Ghalambor's model. Then, after matching the code results with the rates of the 3 wells mentioned in the original work of M. Tabatabaei and A. Ghalambor, sensitivity studies were made on all the reservoir and production parameters in both productivity models. They were to show the effect of changing each parameter on the production rate error. The analysis of results showed that the error comes from a combination of parameters with different weight factors.

A productivity error correlation is the output of the second part of this paper. The correlation is developed by non-linear regression on the results of the sensitivity runs as inputs, and the errors as the output. A neural network model was also developed, using the same inputs, to confirm the reliability of the developed correlation. The correlation could be used to get a rough estimate of the actual production rate of a horizontal well, as well as judge the validity of the infinite borehole conductivity models.
Analysis and Improvement of Calculation Method of Riser Top Tension in Deepwater Drilling
Authors: Meng Wei , Yang Jin , Gao Deli , Hu Nanding , Tong Gang , Deng He , li Lei , Zhao Yihui , Liu Zhengli
Published: March 2016

Top tension plays an important role in stability of riser system. Either excessive or insufficient value of it tends to cause negative effects on risers' proper function and then pose a threat on drilling operation. But there is no unified calculation method about the setting value of riser top tension. Therefore, the purpose of this paper is to establish a calculation method of riser top tension that both meets the requirements of theory and engineering.

The improved method is based on the theory of effective axial force in tubing mechanics. It considers the requirement of risers stability and over-pull force to lower marine riser package (LMRP) in field drilling operation. Take three deepwater wells in South China Sea as examples. Utilizing finite element analysis software ANSYS to model the riser, subsea wellhead and conductor systems respectively, then exerting the calculated top tension and environment load, the analysis results can be used to check the accuracy of the proposed calculation method.

After analyzing the related methods proposed by American Petroleum Institute[1] (API) and Institute of French Petroleum[2] (IFP), it is found that both of them have their limitations. The former one only concentrates on stability but ignores the over-pull force required by LMRP in field operation. The latter one takes the requirement of overpull into consideration though, it regards this force as effective tension rather than true tension. According to the related theories of tubing mechanics, the effects of true axial force and effective axial force on the riser mechanical behavior is analyzed. The results show that, the bottom tensile force to LMRP is determined by true axial force, and the risers' stability depends on effective axial force. Through the force analysis of risers which simultaneously bear the inside and outside pressure, the correspondent mechanical model was established, and a new calculation method of top tension was derived, which modifies the deficiencies of algorithms proposed by API and IFP. The accuracy of this method is verified by the values if field operating and numerical simulation of ANSYS.

The novelty of this method is to propose a calculation method of riser top tension that could improve the deficiencies of API and IFP and meet the requirement of stability and bottom over-pull force to LMRP in field operation.