bluuebunny/crossref_metadata_2025_split huggingface dataset:
Brine Chemistry Effects in Waterflood and CO2 Injection in Carbonate Reservoirs
Authors: Sarma Hemanta K. , Zhang Yi 
Published: September 2014

It has been reported that the waterflood performance in carbonate reservoirs could be significantly ameliorated by tuning the injected brine salinity and ionic composition. Also, it is noted that the brine salinity affects the CO2 injection process. This study looked into such possible effects of brine chemistry on waterflood and CO2 injection for typical UAE carbonate reservoir conditions of high temperature and pressure (T = 120°C and P = 20.68MPa).
Effects on waterflood performance were investigated experimentally by a series of flooding tests at temperatures of 70°C and 120°C. In addition, an imbibition test was conducted at 70°C, followed by wettability monitoring tests at 90°C to investigate the impact of brine salinity variations and ionic compositions on waterflood performance.
The impact of brine salinity on CO2-brine system properties including CO2 solubility in brine, interfacial tension between CO2 and CO2-saturated brine, and density and viscosity of CO2-saturated brine were evaluated through correlation-based studies in conjunction with some experimental data. A mathematical pore-scale model was developed to assess the brine salinity effect on water-isolated oil recovery by CO2 diffusion through water barrier. This study led to the following findings:
(1) Incremental oil recovery could be obtained by either reducing salinity or increasing sulfate concentration of the tertiary injected brine at both 70°C and 120°C. However, the incremental recovery was more remarkable at the higher temperature of 120°C.
(2) At 70°C, lowering the water salinity is more effective than raising the sulfate concentration in injected water in terms of incremental oil recovery. It also exhibited a similar potential for increased oil recovery at 120°C.
(3) Wettability monitoring tests showed that water-wetness of carbonate rock studied could be increased by either reducing the water salinity or increasing sulfate concentration of the surrounding water. This is consistent with the imbibition test, in which wettability alteration towards more water-wetness by low salinity water was noted.
(4) Under typical UAE reservoir conditions, reducing the brine salinity could significantly enhance CO2 dissolution in brine, consequently inducing significant variation to the CO2-brine system properties. This would undoubtedly impact CO2 injection performance.
(5) Under typical UAE reservoir conditions, the capacity and rate of CO2 diffusion through water barrier to oil phase could be significantly reinforced by lowering the brine salinity of the water barrier.
Numerical Study of Two Vessels Seakeeping in Waves
Authors: Zhan Dexin , Bass Don , Molyneux David 
Published: September 2014

This paper presents a numerical study of seakeeping in regular waves for two vessels in close proximity using commercial seakeeping software HydroStar and an in-house code MOTSIM. The objective was to study the possible sheltering effect of the larger vessel (FPSO) on the smaller one (OSV) during personnel transfer between the two vessels, where one vessel was at some angle relative to the other vessel and there was no connection line between them. The study mainly focused on the OSV motion resulting from the interaction of the FPSO when the OSV was at different headings and wave directions. Initially the OSV motions close to the FPSO (and parallel) were compared with those for the OSV alone. For an un-parallel position of the two vessels, an objective function based on the OSV RAOs motion in roll, pitch and heave directions was used to optimize the OSV position. Finally comparisons between HydroStar and MOTSIM results are provided.
The main conclusions are:
1) When the FPSO and OSV are located in parallel, the OSV motions in sway, roll and yaw are larger than the single OSV motions in head waves while surge, heave and pitch are almost the same. The OSV motions in most of the six degrees of freedom are smaller than the single OSV motions when the waves are from other directions (always on the port side of the FPSO), which means that there is a sheltering effect.
2) The simulation results from different OSV rotation angles show that the hydrodynamic interaction between the FPSO and OSV e.g. the sheltering effect is related to the OSV angle and the wave heading. The objective function in roll, pitch and heave RAOs indicates that the OSV should maintain a close to parallel position with the FPSO to minimize motion when the waves come from the port side of the FPSO from 180 to 240 degrees. When the wave direction is around 240 degrees the OSV should have relatively small motion in waves for any OSV rotation angle.
3) A comparison of HydroStar and MOTSIM results shows that the MOTSIM results of a single vessel seakeeping simulation is in a good agreement with HydroStar. In two vessels situation more validation work needs to be done.
Experimental Determination of Roll Damping Coefficient for FPSO
Authors: Seelis Oliver A. , Tao Longbin 
Published: September 2014

The roll damping coefficient is a crucial parameter for several design and operational aspects of FPSOs. The accurate prediction of the coefficient is not a trivial task and generally performed experimentally. A polynomial linearization of the decay test data has been widely applied in the offshore industry. However, research has indicated that for FPSOs with rectangular cross section and attached bilge keels, this methodology may lead to inaccurate damping coefficients.
This paper presents a study on the experimental determination of roll damping coefficients for FPSOs, obtained by free decay tests. For this purpose model tests are executed in the towing tank of the Marine Hydrodynamic Laboratory at Newcastle University. The model is based on the design of a purposely build FPSO, as typically applied in the central North Sea sector. The cross section of the FPSO is boxed shaped with a characteristic knuckle shaped bilge. The tests are conducted using three different bilge keel arrangements. The parametric change in bilge keel size results in the variation of the flow characteristics around the bilge knuckle. The damping coefficients are then established from the decay test data using a polynomial approach, a bi-linear approach and a hyperbolic approach.
A comparison between the damping evolutions obtained with the different methodologies is performed for each bilge keel configuration. Further, a numerical model of the FPSO is created using DNVs Sesam software. With the established damping coefficients, damping matrices are manually defined as an input to Sesam and roll transfer functions are numerically established. The computational determined transfer functions are then compared against the RAOs obtained from the model tests in regular waves to determine the most appropriate methodology.
The damping coefficient for the bare hull is well established by all three proposed methodologies. However, with the attached bilge keels the bi-linear and the hyperbolic methodologies produce damping coefficients reflecting the experimental results more accurately than the polynomial approach, indicating that the recently developed hyperbolic method is a valid alternative, and in certain cases, is more suitable to determine the roll damping coefficient. The experimental measurements could serve as a benchmark for further research and contribute to the practical application of FPSO roll damping determination.
On the Challenges With Pipeline Free Spans in Operational Phase
Authors: Raposo Celso , Fyrileiv Olav , Pereira Antonio 
Published: September 2014

Free span assessment has more and more become an important part of modern pipeline design. The reason for this is partly that the remaining hydrocarbon reservoirs are located in more challenging places, e.g. with very uneven seabed. Another explanation is that the pipeline design codes a few decades ago did not allow for vibrating free spans, while the modern, state-of-the-art pipeline codes, such as DNV-OS-F101 “Submarine Pipeline Systems” (2013) and its Recommended Practices, opens for long spans that are allowed to vibrate as long as the structural integrity is ensured.
In presence of non-cohesive soils and high on-bottom flow velocities significant free span development may occur over the design life, e.g. due to scouring. Such spans may be associated with a fatigue life capacity less than the design life if the spans are assumed stationary. For non-stationary spans with occasional long span lengths this may not be true since the criticality is strongly linked to the persistence of long spans and the prevailing environmental condition. A realistic fatigue assessment must account for the history of the span (i.e. stress cycles encountered for a critical weld) including predictions into the future development.
High costs related to span intervention puts focus on minimizing these costs while still ensuring integrity of the pipeline with respect to vortex induced vibrations (VIV) and associated fatigue damage. On the other hand the potential costs related to fatigue failure of a pipeline (recovery costs, economical loss and environmental consequences) are enormous. Therefore it is essential to ensure that the probability of failure for free spans is within acceptable limits.
One frequent challenge faced with old pipelines in operations survey reports are that they report several free spans. Old pipelines were not designed to allow any vibration and usually there is scanty information about different parameters such as soil conditions, operational parameters, lay tension, environmental data, etc., thus it’s difficult to determine whether it’s necessary to intervene the span or not.
State-of-the-art free span codes are deterministic in their nature. If the new codes are used to evaluate such old pipeline spans, considering all the before mentioned uncertainties in the input parameters, this would eventually lead to over conservative very low time to failures. The outcome will be that many spans need to be fixed immediately or should have failed already. Such a situation leads to a mistaken conclusion about the conservatism of the codes and not on the way they were applied.
This paper discusses some of the challenges often seen with free spans during the operational phase. The objective of the paper is to demonstrate that for in-service pipelines the lack of reliable information about the free spans is the main source of commonly low life encountered and not the methodology used to evaluate the free span. Some of these challenges are discussed in detail and potential ways forward are outlined.
Numerical Simulation of Fatigue Crack Growth of a Welded Structural Component Under Block Program Fatigue Test
Authors: Gotoh Koji , Takuno Masao , Okada Koichi , Kusuba Sadaharu 
Published: September 2014

Numerical simulations of fatigue crack growth of welded structural component were performed under fatigue testing conditions with block loading and constant stress range and the fatigue crack growth profiles were measured under the same loading conditions. In the experiments, fatigue cracks developed at the boxing fillet welded toe and grew toward the top flange plates of the specimens.
An advanced fracture mechanics approach based on the improved effective stress intensity factor range, which is the RPG (Re-tensile Plastic zone Generating) stress criterion, was applied to perform the numerical simulations of fatigue crack growth in the modeled components. A comparison of estimated fatigue crack growth profiles with measured ones verified that a reasonable estimation of fatigue crack growth can be estimated by applying the proposed numerical method.
Selection of an Offshore Petroleum Production System by Evaluating an Environmental Impact Index
Authors: Gonçalves Maiara Moreira , Morooka Celso Kazuyuki , Guilherme Ivan Rizzo 
Published: September 2014

The development of an offshore petroleum production system corresponds to define a set of equipment to make possible oil and gas extraction from an underwater petroleum reservoir. To better comprehension of the process, definition of this production system can be divided into phases. Phase I corresponds to the selection of number of wells and type of the well. Then, following the previous work (Franco, 2003), in the Phase II, the layout arrangement of wells and the set of the stationary Floating Production Unit (FPU) are selected. And, in the Phase III, storage and offloading alternatives for the produced oil and gas are selected.
The present paper aims to identify environmental impacts associated with the each component of an offshore system for oil and gas production, and quantify each of them through indexes. It is expected to support the decision makers to select the best fitted system for a given offshore petroleum field. The increasing needs of petroleum to fulfill the energy matrix demanded in Brazil, the growing concern of the society for keeping the environment clean and the inclusion of an index related to the environment besides the technical and technological indexes usually taken makes it an important contribution to improve the process for selection and decision about the offshore production system. Particularly, it will be fundamental in the adverse condition of the Pre-salt scenario of petroleum production, in ultra-deep water depth and oil and gas with more aggressive contaminants to the system.
The proposed methodology follows a similar procedure for the assessment of environmental impacts through the use of environmental sensitivity index (ESI) and the use of impact matrix (NOOA, 1997; Patin, 1999; Mariano and La Rovere, 2006). For the estimation of environmental impacts, it was defined the ESI of the area to be developed, and it was constructed an impact matrix based on the activities involved in the installation of platform, operational phase and decommissioning of a FPU and the elements from environment. Therefore, this systematic and structured approach allowed incorporating to the process of selection of the offshore production system for an oil and gas field the selection of alternative which combines the best technical and technological characteristics with better aspects from the environment.
Extending the Capabilities of the Mooring Analysis Program: A Survey of Dynamic Mooring Line Theories for Integration Into FAST
Authors: Masciola Marco , Jonkman Jason , Robertson Amy 
Published: September 2014

Techniques to model dynamic mooring lines take various forms. The most widely used models include a heuristic representation of the physics (such as a lumped-mass system), a finite-element analysis discretization of the lines (discretized in space), or a finite-difference model (which is discretized in both space and time). In this paper, the authors explore the features of the various models, weigh the advantages of each, and propose a plan for implementing one dynamic mooring line model into the open-source Mooring Analysis Program (MAP). MAP is currently used as a module for the FAST offshore wind turbine computer-aided engineering (CAE) tool to model mooring systems quasi-statically, although dynamic mooring capabilities are desired. Based on the exploration in this paper, the lumped-mass representation is selected for implementation in MAP based on its simplicity, low computational cost, and ability to provide physics similar to those captured by higher-order models.
To begin, the underlying theories defining the three classes of dynamic mooring line models are identified and explored. This leads to insight into the capabilities of each representation. These capabilities are weighed against the current needs of the FAST wind turbine CAE tool, to which MAP will be coupled. Based on the assessment, a plan for integrating the dynamic mooring line theory into the current MAP structure is developed. Common problems arising from the determination of the model static equilibrium and known issues with numerical stability are addressed. Because MAP is a module that FAST can call, a plan consistent with the FAST modularization framework principles is described. Adding dynamic mooring line capabilities extends the features in MAP and also allows uncoupled analysis to be performed through MAP’s native Python bindings.
Flexible Pipe Modeling Using Finite Macro-Elements
Authors: Provasi Rodrigo , Martins Clóvis de Arruda 
Published: September 2014

Modeling flexible pipes in the local level is not a trivial task and many authors have employed a great amount of time in such task. The non-triviality arises from the various layers and their interaction, which are pretty tough to correctly model. The possible approaches to solve the problem are divided in to major categories: analytical models and numerical models. The analytical ones rely on a great number of hypotheses and, after a great effort, result in a system of algebraic equations. The numerical ones can be further differentiated in the ones developed using commercial software and the other ones using proprietary models.
The authors choose the second way to approach the problem and presented in previous works a group of elements called macro-elements, including a cylindrical element for orthotropic layers, a three dimensional curved beam for helical elements, a rigid connection and a contact element, both dealing with different node displacement natures. These elements take into account the physical and geometrical characteristics of the components. In this paper a pipe model, with a flexible internal core, two tensile armors and an external sheath, will be simulated and its the results will be checked against commercial software and commented.
Direct Numerical Simulations of Wall Proximity Effect on Single and Tandem Cylinders
Authors: Khandelwal Prateek , Jaiman Rajeev K. , D’Souza James Evon , Mak Chan Keet 
Published: September 2014

Subsea pipelines placed at or near the seabed are exposed to waves and underwater currents. The unstable seabed, irregular terrain, erosion of sediments or installation procedures may lead to free span in sections along the length of pipelines. This problem can be explained in simplified terms as a cylinder near an impermeable wall subjected to boundary layer based shear flow. It is common practice to use fixed cylinder hydrodynamic coefficients (drag, lift, and interia) to calculate the pipeline stability with the assumption that the pipeline is either trenched or lying on the seabed. However, due to the gap between the pipe and the seabed, the force coefficients have a strong dependence on the relative gap.
In this paper, a moving wall is considered rather than a fixed wall to avoid the confusing interaction of wall boundary layer and thus focus completely on wall proximity effects to evaluate the lift and drag forces. In particular, the wall-induced lift force is due to two competing mechanisms in subsea pipelines. First, the vorticity generated at the surface of the cylinder cross-section advects and diffuses downstream. The presence of a nearby wall breaks the axisymmetry of the wake vorticity distribution. The resulting induced velocity also breaks the symmetry and results in an effective lift force that tends to move the pipeline away from the wall. Second, from inviscid theory, one can argue that the flow relative to the cylinder will accelerate faster in the gap between the cylinder and the wall. The resulting low pressure in the gap will induce a lift force directed toward the wall. In the first part, we focus on the wall-induced lift force in the finite Reynolds number regime using a Spectral Element method to perform direct numerical simulations (DNS) with high accuracy. The effects of gap ratio will be investigated in detail to characterize the oscillating forces on the cylinder. In the second part, this paper will focus on studying how seabed can affect two tandem cylinder arrangements as a function of spacing and the interaction of wall-induced forces with the wake dynamics between the two cylinders.
Methodology to Obtain the Life Cycle Mooring Loads on a Semisubmersible Wind Platform
Authors: Guanche Raúl , Meneses Lucía , Sarmiento Javier , Vidal César , Losada Íñigo 
Published: September 2014

Nowadays there are few methodologies related with the design of mooring systems for floating offshore wind platforms. The ones used until the moment are inherited from the oil and gas industry. Because of that, mooring loads may be incorrectly estimated. This study presents a validated methodology in order to estimate the loads of the moorings of offshore floating platforms along the life cycle of the structure.
The methodology is based on an extensive laboratory test data base carried out in a wave basin of the University of Cantabria. The proposed methodology has been applied to a floating semisubmersible platform (similar to the one in Agucadoira by Principle Power).
The methodology is composed by a few steps. The first step consist on the selection of the most representative sea states of a long term met-ocean data base through a selection technique named MDA (Maximum dissimilitude algorithm). Afterwards, mooring system loads and platform motion are numerically simulated. SESAM (DNV) numerical model has been used in this particular application. SESAM numerical model was previously calibrated based on the laboratory tests. Finally, based on a multidimensional interpolation technique named Radial Basis Function life cycle mooring system loads were reconstructed.
A sensitivity analysis of the methodology were carried out. Based on it, it can be concluded that selecting 1000 sea states with the MaxDiss technique, life cycle mooring loads can be accurately predicted.
Alternative Method for Estimation of Design Extremes for Moored Floaters
Authors: Bonnaffoux Guillaume , Melis Cécile 
Published: September 2014

After having relied for decades totally on small scale model tests, the design of anchoring systems for moored floaters like FPSOs is now widely performed numerically. Estimation of design maxima during mooring analyses requires calculating system response for a large number of sea states in order to screen all possible scenarios between wind, waves and current parameters. In addition, the slow-drift response motions of the system constituted by the floater and the anchoring system are highly dependent of the wave elevation realization, which is not an input parameter of the simulations and can lead to extremely variable responses.
This is generally addressed by designers by performing the analysis for the same sea state and varying the wave group spectrum (or wave components phases) a large number of times N (20–50 realizations is a typical range, see Refs [4], [5]). For these N realizations, N response maxima are extracted, and a distribution of response extremes is derived, from which the response level is extracted. In terms of computational cost, performing N 3-hour simulations to derive N values of extreme response is extremely expensive.
The paper will focus on methods that can be employed to reduce the computational cost of analyses. In a first step, the rapidity of statistical convergence of response estimates depending on the system will be investigated. This will allow pre-determining the number of sea states realizations required to reach a satisfactory convergence of response. In a second step, a mean of improving the computational efficiency of calculations carried-out to reach the statistical convergence will be proposed.