bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Environmentally Friendly Alternative for the Conventional Acids Used in Acid Fracturing of Carbonate Reservoirs
Authors: Nawik Adisak , Taylor Kyle , Barati Ghahfarokhi Reza 
Published: October 2016

The acid fracturing techniques developed for well stimulation purposes have been applied to maximize oil production while bypassing the near wellbore damage. Commonly used acids such as hydrochloric acid (HCl) and hydrofluoric acid (HF) damage equipment, are not environmentally friendly and, most importantly, they are harmful to oil field workers. Moreover, transportation of such fluids to the well-head and neutralization of the flow-back products is costly.
The Ultra Series FF-01 is an environmentally- and equipment-friendly alternative to the commercially available products. The Ultra Series FF-01 is very acidic, its pH is less than 1, and has a slower reaction rate compared to the HCl. It can work up to 72 times longer than hydrochloric acid. Most importantly, it is biodegradable and is non-corrosive to the field equipment.
Acid conductivity measurement tests were designed to simulate acid fracturing for comparing the performance of acid fracturing fluids. The main objectives of this study is to compare the ability of Ultra Series FF-01 samples in etching the surface of carbonate rocks by measuring the conductivity of the simulated etched fracture. The two acid fracturing fluids that are used in these experiments are the Ultra series FF-01 and a conventional 15% hydrochloric acid with the iron control agent, non-emulsifier, and corrosion inhibitors. The injection rate is at 100 mL/min and the total time of injection is 1 hr. Experiments were performed on carbonate rocks at 40° C and 70° C and the leak-off pressure was set to be 100 psi lower than the overall pressure. Then the conductivity was measured at different closure stress after the injection time is complete.
Conductivity after etching by the Ultra series FF-01 was significantly improved compared to that obtained with 15% hydrochloric acid with additives when the leak off was set at 100 psi lower than the system pressure for all values of closure stress. It was very evident from the difference in the etching patterns between the two fluids. The etching pattern that was created by the Ultra series FF-01 was in the shape of human veins, visible and connected. In contrast, the surface of the core samples that were etched by 15% hydrochloric acid with additive were bouncy but shallow, producing inferior conductivity. In addition, the performance of the Ultra series FF-01 was slightly better than 15% hydrochloric acid with additives when the leak off pressure was set at 50 psi lower than the system pressure for all closure stress pressure except for 1000 psi.
Numerical Estimation on Stress Intensity Factors for Surface Cracks in a Welding Residual Stress Field
Authors: Gadallah Ramy , Osawa Naoki , Tanaka Satoyuki 
Published: October 2016

Cracks are frequently found in complicated residual stress fields. It is therefore necessary to take the influence of stress field into account when calculating stress intensity factors (SIFs). In this study, SIFs for 3-D surface cracks in a flat plate model and a T-butt welded model with different dimensions are evaluated using the superposition method. To implement the superposition method, two codes are utilized, a commercial nonlinear finite element (FE) code that will progress the domain integral method using MSC Marc. The other is an open source research code that will progress the interaction integral method using WARP3D, both solutions will be applied to evaluate the SIFs. The crack face traction term (CFT-term) is neglected for the MSC Marc solution. However, the CFT-term is included in the WARP3D solution to examine the significance of this term on the accuracy of the solutions obtained by crack face traction. The SIFs calculated by direct solution, for a flat plate model and a T-butt welded model, are validated through well-established results. The accuracy of the superposition method is verified by comparing the SIFs obtained by crack face traction with those given by direct solution.
It was found that the difference between the solutions at the deepest point of the crack was less than 5%, even when the CFT-term in the domain integral method was neglected. This shows that commercial nonlinear FE codes that neglect the CFT-term can be applied for engineering problems under the conditions examined in this study. As well, the CFT-term in the interaction integral method showed a significant improvement in the accuracy of the solutions given by crack face traction for a flat plate model. It was found that the difference between the solutions was less than 0.5% at the crack deepest point.
NDP Riser VIV Model Test With Staggered Buoyancy Elements
Authors: Wu Jie , Lie Halvor , Constantinides Yiannis , Baarholm Rolf J. 
Published: October 2016

The Norwegian Deepwater Program (NDP) has over several years working on conceptual development and design of new steel riser solutions for deep water and harsh environment. For the steel lazy wave riser (SLWR) design, the buoyancy section is a critical segment. When subjected to current, both the buoyancy elements and the riser may experience vortex induced vibrations (VIV), which can lead to fast accumulation of fatigue damage and amplified drag loads. As part of developing robust SLWR, it is crucial to understand the current induced loads and responses on various staggered buoyancy configurations.
In order to investigate the interaction of bare pipe section and buoyancy elements and its effect on VIV, hydrodynamic model tests were carried out in MARINTEK’s ocean basin in 2014. The test pipe is 38 m in length and 3 cm in diameter. The length of each buoyancy element 0.15 m and its diameter is 0.15 m. The ratio between buoyancy element diameter and riser diameter is 5. VIV response may depend on the spacing ratio of the length of the buoyancy segments and the gaps between two adjacent buoyancy elements, aspect ratio of the buoyancy element, and coverage percentage of buoyancy elements. Hence these parameters were varied and 6 different staggered buoyancy configurations were tested in uniform flows. The use of strakes to suppress VIV was also evaluated. The primary objective is to determine a range for these parameters that leads to the smallest VIV curvature (and hence an optimal riser fatigue design).
The shedding frequency of the bare riser section is significantly higher than the buoyancy element due to its smaller diameter. Therefore, the bare riser section will excite much higher modes. As observed from the present tests, the fatigue damage is dominated by the bare riser component for all of the test configurations. The CF displacement of cases with the highest buoyancy coverage (50%) is often dominated by the vortex shedding of the buoyancy element. The use of stakes can effectively suppress the vortex shedding and leads to lowest fatigue damage in the test. In addition, the non-dimensional frequency of the buoyancy element is low (about 0.087–0.122) due to its small aspect ratios (1/1 and 2/1) in present tests. The vortex shedding of the buoyancy element seems to be weakened when the spacing ratio is larger than 1/1, which is different than earlier tests using buoyancy element with larger aspect ratio (≥5/1). The impact on the SLWR design is evaluated based on both present and other relevant model tests results.
Towing Analysis of Multi-Cylinder Platform for Offshore Marginal Oil Field Development
Authors: Zhao Zhijuan , Tang Yougang , Wu Zhirong , Li Yan , Wang Zhenkui 
Published: October 2016

As the development of offshore marginal field becomes a heated topic, various design selections of offshore platform have already been put forward in the community such as Sevan SSP, IQFP-FPSO, octagonal FPSO or sandglass-type FDPSO. In this paper, a new Muliti-Cylinder FPSO (MCPSO) with section pile foundation is proposed for developing offshore marginal field in South China Sea. And the structure design in detail has been described.
The MCPSO consists of six cylindrical concrete tanks and six suction piles. The suction piles can be raised up during platform towing process. Considering the effects of tanks and piles on the towing stability, both intact and damage stability analysis of MCPSO were performed under different towing conditions. The influence of ballast ratio, towing direction and different damaged modes on the towing stability is analyzed.
The results indicate that the MCPSO has the characteristics of self-installation, movable, reusable and so on, which is suitable for the development of marginal oil field. The MCPSO filled with 40% seawater in ballast tank and towed in 90 direction has the best intact and damage stability characteristic.
Hydrodynamics of Side-by-Side Fixed Floating Bodies
Authors: Chua Kie Hian , Eatock Taylor Rodney , Choo Yoo Sang 
Published: October 2016

Safety of cargo transfer operations between side-by-side vessels depends on accurate modelling of hydrodynamic behavior, especially in terms of predicting the gap free surface elevations between the two vessels. The common industry practice of using linear potential flow models to study these interactions over-predicts the free surface elevations, due to the fact that potential flow does not include viscous dissipation effects such as flow separation at hull corners and skin friction. This may result in inaccurate projections of the time-window when these operations can safely take place. This is an important aspect for developments such as Floating Liquefied Natural Gas (FLNG) platforms, where side-by-side cargo offloading is an essential operation.
In a recent research [1], an approach of splitting the amount of energy lost through viscous dissipation (calculated from three-dimensional viscous CFD simulations) into components representative of the flow phenomena has been proposed. Using the approach, referred to as component energy dissipation, the amount of energy lost due to vortex shedding and skin friction can be estimated. Modifications to linear potential flow were also proposed in the referenced research, such that the energy loss components can be converted into dissipative coefficients that are used in terms added to the free surface and body boundary conditions. By combining use of the component energy dissipation approach and the modified dissipative potential flow model, better predictions of gap hydrodynamic interaction can be obtained, compared to using conventional potential flow.
In this paper, results from viscous simulations of two identical fixed-floating side-by-side barges of 280m (length) × 46m (breadth) × 16.5m (draught) under excitation from regular incident waves are presented, and compared with corresponding results from the modified dissipative potential flow model. Two types of side-by-side hull configurations were investigated, the first using rectangular barges with sharp bilge corners at varying gap distances and the second using barges with rounded bilge corners of varying radii at a fixed gap distance. Estimation of the dissipative coefficients used in the modified potential flow model, calculated from the viscous results, will also be discussed. The comparison of results serves both as a validation of the modified potential flow model, and to highlight the importance of including viscous dissipation when analyzing hydrodynamic interactions.
Experimental Investigation of Water Exit Under Hydrophobic Effects
Authors: Guzel Bulent , Korkmaz Fatih C. 
Published: October 2016

Prediction of hydrodynamic loads during water exit of a body is of a great importance in designing the marine vehicles that take off from the free water surface such as sea planes and wing-in-ground effect vehicles (WIG), and that pierce through the free surface like missiles and submarines. The results of an experimental investigation on water exit of two different geometries, sphere and flat plate, with hydrophobic surfaces are presented in this paper. With and without the hydrophobic effects present, different fluid dynamics phenomena like free surface evolution, deformation and break up of free surface, wave generation, splash, air entrapment and water detachment from the solid surfaces during a water exit event have been examined. The non-dimensional exit coefficient, Ce is a function of the total vertical hydrodynamic force which depends on the geometry of the object and the hydrodynamic conditions along with the water parameters. Our study is aimed at understanding and modeling the nonlinear free surface effects and the dynamics of water exit under an extended range of parameters including hydrophobic effects.
In this study, due to lack of the experimental data on the water exit problem in literature, water exit tests have been set up, first for initially partially immersed spheres and flat plates, with their center above the free surface, to be towed vertically from the water surface at various speeds. Secondly, buoyancy driven water exit of a fully immersed sphere is investigated. It is observed that when the sphere rises up, it first starts deforming the free surface, and then pierces into it. The thin water layer attached to the surface of the sphere is drawn back to the test tank as the sphere moves further upward. This causes breaking of the free surface, air entrapment and wave generation in the water tank.
From digital images captured using a high speed camera, free surface breakup and water detachment at different velocities are observed and the time evolution of the water detachment and the exit characteristics are measured during a water exit event. The position of the sphere and its velocity are plotted against time. A detailed measurement of the global loads on the test objects during exit is carried out by employing strain gauges.
We also showed the effects of water detachment on the test bodies during exit and after fully exited via strain gauges. All this data is also collected under the hydrophobic effects, to show how the change in surface characteristics would have significant impacts on the water exit phenomenon. Analyzing the difference in occurrence of water flow separation, the change in kinetic energy of the fluid and the free surface deformation under the hydrophobic effects may help give a better explanation of the phenomena observed during water exit and improve the design characteristics of marine structures for a water exit event.
Practical Review on Fatigue Damage Estimation Under Combinations of Global and Local Loadings
Authors: Cho Tae Min , Chun Min Sung , Kim Hyun Joe , Lee Dong Yeon , Kim Boo Ki 
Published: October 2016

In this paper, reviews on the fatigue damage estimation are presented in case that both the global and the local loadings are applied and two practical approaches are proposed if the statistical data of the local loading are not available. So far the fatigue damage has been estimated through Rules from Classification of Societies if the statistical data such as the standard deviation and the up-crossing rate of the stress processes are available. However, in many cases, it’s hard to prepare enough data for the fatigue damage estimation, which results in very severe design.
Hence two practical approaches are presented which can be applied if the statistical data of the local loading are not available. In practice, only the maximum stress range and the total cycles of the local loading are available very often. In the practical approach 1, it is assumed that the maximum stress range always occurs during the total cycles. Then, the local fatigue damage is very conservatively estimated and the total fatigue damage is obtained by the way of summation of the global fatigue damage and the local fatigue damage. In the practical approach 2, the local fatigue damage is estimated based on the assumption of the Weibull fitted local loading. And the use of the cube root summation is proposed between the global fatigue damage and the local fatigue damage. The presented two practical approaches are applied to the side appurtenances of a FPSO and the resultant fatigue damages are compared and discussed. The results of this study can be expected as practical and useful data for the fatigue analysis of the marine and offshore structures.
Rapid Assessment of Hull Girder Collapse for Corroded Double Hull Oil Tanker After Collision
Authors: Noh Sung Hwan , Seo Jung Kwan , Paik Jeom Kee , Youssef Samy A. M. 
Published: October 2016

Corroded tankers might be subjected to a very serious structural damage if involved in collision accidents. For understanding or preventing the collision accidents, various studies are being proposed by researchers to improve the analysis method.
In this paper, four types of double hull oil tankers (Panamax, Aframax, Suezmax and VLCC) are used. Probabilistic approach is used to create ship-ship collision scenarios for each target structure and the ultimate longitudinal hull girder strength of the hypothetical oil tanker’s hull cross-section. The ALPS/HULL is used to simulate and is intelligent supersize finite element method (ISFEM) software. A relevant probability density function (PDF) is introduced using the results from finite element simulations of the ship-ship collisions, which is commonly used to predict residual strength.
Development of Dual-Lifting Technique for Installation of Topside Mega-Modules
Authors: Jung Dong Woo , Kim Hyun Joe , Ji Hae Sung , Jeong Hyoen Su , Nam Mihee , Lee Dong Yeon , Kim Booki , Jin Jong Dae 
Published: October 2016

As many deep-sea oil and gas fields are being developed, floating platforms becomes larger with more complicated topsides. However, the construction time is demanded to be shorter to meet the overall project schedule. The use of very large topside modules is one of the effective ways to reduce the integration time and decrease the possibility of fabrication defects.
The Ichthys Project’s CPF (Central Process Facility) is currently being constructed at Samsung Heavy Industries (SHI). The CPF will be the world’s largest production semi-submersible platform. The hull is constructed on the Offshore Floating Dock and most of the topside modules are prepared at workshops and integrated by floating cranes on the hull.
To maximize production efficiency in terms of reduced integration time and reworks, several topside modules are assembled into a larger module weighing up to 7,400 tonne spanning 150m long. Such large module cannot be handled by a single 8,000 tonne F/C, the largest crane that SHI owns. This fact initiated the idea of dual-lifting with a combination of the two F/Cs (8,000 tonne and 3,600 tonne) which enables lifting, transportation and integration of the mega-modules properly and safely without building a larger capacity F/C. Using different sized F/Cs increases the flexibility of the operation of the F/Cs.
To ensure safety during the dual-lifting, the two F/Cs are synchronized to be controlled as a single crane unit. During hoisting, all the measured data such as loads and positions of the hooks, and rotation of the module, are monitored in real time basis and used to hoist the module automatically. All the systems are designed to be redundant. Additional engineering works are performed to check the safety such as 1) structural analysis to investigate the structural safety with out-of-phased motions at boom-tip 2) time-domain analysis and 3) model test in ocean basin with the operation scenarios in real environments to obtain the dynamic load factors and the guidance on the operation limits in terms of wave heights. The two crane barges are moored side-by-side using fenders and mooring lines, and tug operation conditions are planned not only to move but also to push the two barges from sideways to be moored tightly, which minimizes the possibility of relative motions between the two barges.
The developed system had been applied to the integration of all the modules successfully weighing from 4600 to 7400 tonne. It is expected to be applied to many other offshore projects to keep the construction schedule on time. This paper will address and share the technical experiences obtained during the dual lifting of the mega-modules for the Ichthys Project’s CPF.
Full Scale Reeling Simulation Tests of Girth Welded X60 HFW Linepipe
Authors: Sadasue Teruki , Igi Satoshi , Oi Kenji , Yabumoto Satoru 
Published: October 2016

The reel-lay method is a fast and cost efficient installation process for offshore rigid steel pipelines. Pipelines installed by the reel-lay method are plastically deformed due to reeling, unreeling, aligning and straightening during pipeline installation. Therefore, local buckling is one of the major concerns from a view point of integrity in linepipes, especially around girth welds where strength mismatching arises due to adjacent pipes with different yield strength. One the other hand, the change in mechanical properties of linepipes during reel-lay, including coating process (e.g. 250°C) and long time exposure (e.g. 250°C aging) after installation is also important in order to guarantee safety of linepipes. Furthermore fracture toughness at girth weld Coarse-grain HAZ (CGHAZ) after reeling and aging should be clear to prevent brittle fracture of offshore linepipes in service.
In this study, full scale reeling simulation tests of girth welded X60 HFW (High Frequency electric resistance Welded) linepipes with OD; 323.9mm and WT;15.9mm after full body heat treatment (coating simulation) were conducted at 5cycles and 2cycles reeling and straightening situations when yield strength mismatches are present between adjacent pipes around girth welds. Localized strain concentration was observed near girth welds by strength mismatching of adjacent pipes. DNV ovality increased with increasing reeling and straightening cycles, however the ovality did not exceed 10%, which was a criterion value for local buckling, after 5cycles reeling simulation test. The change ratio of wall thickness after full scale reeling simulation tests were about ±2% (within DNV-OS-F101 tolerance) regardless of circumferential and longitudinal direction of pipes. Longitudinal tensile properties could be characterized by axial last introduced plastic strain. That is, in the positive number of last introduced plastic strain, YS and Y/T increased, while uEl decreased by work hardening effect. On the other hand YS and Y/T decreased, while uEl increased at the negative number of last introduced plastic strain by Bauschinger effect. Circumferential tensile properties could be also characterized by axial last introduced plastic strain. Yield strength and Y/T slightly increased while uniform elongation slightly decreased by aging at longitudinal and circumferential direction. Tensile properties did not change irrespective of the number of cycles of reeling simulation tests. After 5cycles reeling simulation test and aging, girth welded CGHAZ CTOD values were over 0.4mm at −20°C and Charpy absorbed energy were over 200J at −30°V, therefore, it was considered that the brittle fracture of the girth welded linepipe unlikely occur at reeling and aging situation in this study.