bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proper Modeling of Diffusion in Fractured Reservoirs
Authors: Hoteit Hussein 
Published: February 2011

Abstract
Diffusion may play a key role in a number of oil recovery processes such as heavy oil and naturally fractured reservoirs. In fractured media, several laboratory experiments and numerical studies showed that CO2 injection can improve recovery. Molecular diffusion, gravity drainage, and oil swelling are the main contributing mechanisms. Proper modeling of diffusion of hydrocarbon mixtures at the reservoir PVT and geological conditions is not a trivial task. The challenge is in computing the diffusion coefficients for the non-ideal multicomponent mixtures in oil and gas phases, and in physically accurate modeling of the diffusion driving force. One common approach in most simulators is to use the classical Fick's law which simplifies the multicomponent diffusion fluxes by only considering the main-diffusion (diagonal) terms and neglecting the cross-diffusion (off-diagonal) terms. The diffusion fluxes are assumed independent and the diffusion driving force of each component is proportional to the component self concentration gradient. In this work, we demonstrate analytically and numerically that this simplified approach may have a major inconsistency related the flux balance constraint and, in some applications, it may fail to capture the right direction of diffusion as a result of neglecting the dragging effect. We propose an alternative model based on the generalized Fick's law in which diffusion coefficients are calculated as a function of temperature, pressure, and composition. The proposed approach can be seen equivalent to the Maxwell-Stephan model in which the diffusion driving force is the chemical potential instead of the composition gradient. We also tackle anbook problem that may occur in fractured media when fractures get fully saturated with gas in an under-saturated oil surrounding. Intra-phase gas and oil diffusions will not be initiated due to the discontinuity of phases between the fracture and the rock matrix. The proposed approach in the literature that allows for direct gas-to-oil diffusion may not have a sound bases for issues related to the driving force and the estimation of the mass transfer coefficients. We provide a solution for the cross-phase diffusion flux based on the assumption of having chemical equilibrium at the gas-oil contact. Several numerical examples are provided.
Use of Reduced-order Models for Improved Data Assimilation within an EnKF Context
Authors: He J. , Sarma P. , Durlofsky L. J. 
Published: February 2011

Abstract
Reduced-order modeling represents an attractive framework for accelerating computationally expensive reservoir simulation applications. In this paper we introduce and apply a reduced-order modeling approach for history matching. The method considered, trajectory piecewise linearization (TPWL), has been used previously for production optimization problems, where it has provided large computational speedups. The TPWL model developed here represents simulation results for new geological models in terms of a linearization around previously simulated (training) cases. The high-dimensional state space is projected into a low-dimensional subspace using proper orthogonal decomposition (POD). The geological model is represented in terms of a Karhunen-Loeve expansion of the log-transmissibility field, so both the reservoir states and geological parameters are described in a very concise way. The method is incorporated into an Ensemble Kalman Filter (EnKF) history-matching procedure. The combined technique enables EnKF to be applied using many fewer (high-fidelity) reservoir simulations than would otherwise be required to avoid ensemble collapse. More specifically, it is demonstrated that EnKF results using 50 high-fidelity simulations along with 150 TPWL simulations are much better than those using only 50 high-fidelity simulations and are, in fact, comparable to the results achieved using 200 high-fidelity simulations.
Using Multiscale Regularization to Obtain Realistic Optimal Control Strategies
Authors: Shuai Yuanyuan , White Christopher D. , Zhang Hongchao , Sun Ting 
Published: February 2011

Abstract
Smart well technology is attracting increasing attention because it promises to add operation flexibility and potentially increases oil recovery. However, it remains difficult to find the best strategy for production optimization. One challenge is to find a good optimization algorithm, as some optimization algorithms require prohibitive work to compute the gradients of the objective function with respect to the well controls. These methods also require access to the simulator code, which makes them difficult to use with commercial software. Another challenge is to find a reasonable frequency for well control adjustment: adjusting well controls too frequently imposes unrealistic control burdens on operations, increasing well management cost. Moreover, high-frequency control adjustment increases the risk of optimization algorithms being trapped at local optima as the problem is more under-determined. On the other hand, excessively low-frequency control adjustment may not truly optimize oil recovery.
To address these issues, two simulator-independent optimization algorithms were investigated: ensemble-based optimization (EnOpt) and bound optimization by quadratic approximation (BOBYQA). Multiscale regularization was applied to both to find appropriate frequencies for well control adjustment. In a synthetic case study, if multiscale regularization was not used, then EnOpt converged to a higher net value of production than BOBYQA —even though BOBYQA uses second order Hessian information (EnOpt uses first order gradients). BOBYQA performed comparably only if multiscale regularization was used. After multiscale regularization, both methods obtained net value of production (NVP) that equalled or exceeded unregularized optimization, with simpler well control strategies and convergence in fewer iterations.
Comparison of Two Methods for Speeding up Flash Calculations in Compositional Simulations
Authors: Belkadi Abdelkrim , Yan Wei , Michelsen Michael L. , Stenby Erling H. 
Published: February 2011

Abstract
Flash calculation is the most time consuming part in compositional reservoir simulations and several approaches have been proposed to speed it up. Two recent approaches proposed in the literature are the shadow region method and the Compositional Space Adaptive Tabulation (CSAT) method. The shadow region method reduces the computation time mainly by skipping stability analysis for a large portion of compositions in the single phase region. In the two-phase region, a highly efficient Newton-Raphson algorithm can be employed with initial estimates from the previous step. The CSAT method saves computation time by replacing some of the phase split calculation in the two-phase region with pre-stored flash calculation results. The stored results can be used when the new feed composition is on one of the stored tie lines within a certain tolerance. The number of tie lines stored for comparison and the tolerance set for accepting the feed composition are the key parameters in this method since they will influence the simulation speed and the accuracy of simulation results. Inspired by CSAT, we proposed a Tieline Distance Based Approximation (TDBA) method to get approximate flash results in the two-phase region. The method uses the distance to a previous tieline in the same gridblock to decide whether the approximation should be made. Comparison between the shadow region approach and the approximation approach, including CSAT and TDBA, has been made by using a slimtube simulator where the simulation temperature and the simulation pressure are set constant. It is shown that TDBA can significantly improve the flash calculations in the two-phase region.
On Interplay of Capillary, Gravity, and Viscous Forces on Brine/CO2 Relative Permeability in a Compositional and Parallel Simulation Framework
Authors: Delshad Mojdeh , Kong Xianhui , Wheeler Mary F. 
Published: February 2011

Abstract
The effectiveness of CO2 storage in saline aquifers is governed by interplay of capillary, viscous, and buoyancy forces. Recent experimental data reveals the impact of pressure, temperature, and salinity on interfacial tension (IFT) between CO2 and brine. The dependence of CO2-brine relative permeability and capillary pressure on IFT is also clearly evident in published experimental results. Improved understanding of the mechanisms that control the migration and trapping of CO2 in subsurface is crucial to design future storage projects that warrant long term and safe containment. Simulation studies ignoring the variation in interfacial tension and its effect on petrophysical properties of trapped CO2 saturations, relative permeability and capillary pressure have a poor chance of making accurate predictions of CO2 injectivity and its migration. We have developed and implemented a general relative permeability model that combines effects of pressure gradient, buoyancy, and IFT in an Equation of State (EOS) compositional and parallel simulator. The significance of IFT variations on CO2 migration and trapping is assessed.
A Unified Thermal Wellbore Model for Flexible Simulation of Multiple Tubing Strings
Authors: Stone Terry W. , Bennett James , Edwards David A. , Law David Hin-Sum , Pallister Ian 
Published: February 2011

Abstract
Increasingly, operators around the world are using wells with multiple tubing strings to improve both injection and production of fluids in a reservoir. Many operators are beginning to use this technology for designing and optimizing thermal, heavy oil recovery. For example, steam chamber development in a Steam Assisted Gravity Drainage (SAGD) process along a horizontal well pair is often irregular and dual tubing strings may help to even out both injection and production. Problems that operators have with multiple tubing strings in wells include both their control and design. There is a need for a rigorous, accurate and robust method to model these wells as part of the reservoir simulation stage of field planning and development in order to design these wells to improve and optimize oil production and net present value (NPV).
This paper describes a unified thermal wellbore model that fulfills these requirements. The wellbore model allows flexible control of THP, gas lift rates, injection and production rates for each of the tubing strings. There are additional features for optimizing various aspects of the well operation using instantaneous parameters. Improved accuracy in modeling the multiphase flow of fluids and energy is obtained by allowing the tubing strings to consist of multiple segments and branches containing groups of segments. Each segment has its own set of physical parameters including pressure, temperature, phase holdups and frictional/gravitational/accelerational heads. Any number of segments are allowed, the segments are not confined to the grid and can even be specified outside the grid (up to surface) and a flexible conductive heat transfer facility allows multiple heat transfer paths to exist to and from each segment. Additional facilities are described which allow control and optimization of wells and/or individual tubing strings in addition to controllable devices (ICDs, FCVs) using instantaneous or longer term parameters. Two case studies are presented which illustrate some of the simulation workflows. These studies are based on fluid and reservoir properties and well designs typical of the Surmont reservoir which is part of the McMurray formation in Alberta Canada.
Multiscale Finite Volume Method for Non-Conforming Coarse Grids Arising from Faulted Porous Media
Authors: Hajibeygi H.. , Deb R.. , Jenny P.. 
Published: February 2011

Abstract
The multiscale finite volume (MSFV) method is extended to account for non-matching coarse grids arising from faulted porous media. To obtain accurate quantities at the coarse scale, basis and correction functions are computed in extended local domains near the fault regions. With the new framework it is shown that the MSFV results are very close to the fine-scale reference solutions. Finally, to improve the quality and to extend the applicability of the framework, an iterative MSFV method for faulted reservoirs is devised; similar to the recently proposed i-MSFV method for conforming coarse grids by Hajibeygi et al. (2008). Convergence histories of the new i-MSFV method are shown for different homogeneous and heterogeneous test cases. It is concluded that this extension of the MSFV method is very flexible and allows to deal with complex geometries such as faulted reservoirs.
Development of a Transient Mechanistic Two-Phase Flow Model for Wellbores
Authors: Shirdel Mahdy , Sepehrnoori Kamy 
Published: February 2011

Abstract
Two-phase flow occurs during the production of oil and gas in the wellbores. Modeling this phenomenon is important for monitoring well productivity and designing surface facilities. Since transient time period in the producing well is usually shorter than reservoir time steps, stabilized flow is assumed in the wellbore. As such, semi-steady state models are used for modeling wellbore dynamics. However, in the case that flow variations occur in a short period of time (i.e., gas kick during drilling) the use of a transient two-phase model is crucial.
A great deal of research has been conducted to study transient two-phase flow in wellbores. However, there is lack of a comprehensive two-fluid model in the petroleum literature. In this paper, we present an implementation of a pseudo-compositional, thermal, fully implicit, transient two-fluid model for two-phase flow in wellbores. In this model, we solve gas/liquid mass balance, gas/liquid momentum balance, and two-phase energy balance equations to obtain five primary variables: liquid velocity, gas velocity, pressure, holdup, and temperature. This simulator can be used as a stand-alone code or can be used in conjunction with a reservoir simulator to mimic wellbore/reservoir dynamic interactions. In our model, we consider stratified, bubbly, intermittent and annular flow regimes using appropriate closure relations for inter-phase and wall shear stress terms in the momentum equations. In our simulation, we found that the inter-phase and wall shear stress terms for different flow regimes can significantly affect the model's results. In addition, the inter-phase momentum transfer terms mainly influence the holdup value.
The outcome of this research leads to a more accurate simulation of multiphase flow in the wellbore and pipes, which can be applied to the surface facility design, well performance optimization, and wellbore damage estimation.
Comparison of Discrete-Fracture and Dual-Permeability Models for Multiphase Flow in Naturally Fractured Reservoirs
Authors: Moinfar Ali , Narr Wayne , Hui Mun-Hong , Mallison Bradley , Lee Seong H. 
Published: February 2011

Abstract
Two discrete-fracture models (DFMs) based on different, independent numerical techniques have been developed for studying the behavior of naturally fractured reservoirs. One model is based on unstructured gridding with local refinement near fractures, while in the second model fractures are embedded in a structured matrix grid. Both models capture the complexity of a typical fractured reservoir better than conventional dual-permeability models, leading to a more accurate representation of fractured reservoirs.
The accuracy of the DFM approaches is confirmed by their match with a structured, grid-aligned, explicit-fracture model in tests involving capillary imbibition during water flooding and gravity drainage in oil-gas systems. The DFMs are insensitive to grid orientation. Simulations also show consistency and agreement of results of the DFM methods in synthetic models with complex fracture patterns. Our simulations indicate that conventional dual-permeability approaches are appropriate when the fracture system is very sparse relative to the grid spacing. In these situations a DFM can be used as the basis for defining dual-permeability model parameters. However, conventional dual-permeability approaches are inadequate in the presence of high localized anisotropy and preferential channeling. When used with general purpose reservoir simulators, both DFMs show computational performance that is comparable to that of dual-permeability models.
New Frontiers in Large Scale Reservoir Simulation
Authors: Dogru Ali H. , Fung Larry S. , Middya Usuf , Al-Shaalan Tareq M. , Byer Tom , Hoy H. , Hahn W. A. , Al-Zamel Nabil , Pita J. , Hemanthkumar K. , Mezghani M. , Al-Mana Abdulrahman , Tan J. , Dreiman W. , Fugl A. , Al-Baiz Abdulaziz 
Published: February 2011

Abstract
Giant reservoirs of Middle East contain substantial portion of the world's total hydrocarbons. Accurate simulation of these reservoirs requires as many as billion cells. A billion-cell parallel reservoir simulator was first presented in 2009.
This paper discusses the progress in the past two years and future projections.
In addition to black oil models, paper presents a large full field compositional model involving over billion unknowns. Throughout the paper grid size effects, computational work distribution and parallel scalability are discussed and illustrated. Paper also presents futuristic technologies for building and analyzing large simulation models.
Good Practice in Controlling Employees' Exposure to Noise and Vibration in the Oil and Gas Industries
Authors: Appleton Bruce 
Published: February 2011

Abstract
There are notable examples of good practice in control of noise and vibration in the offshore oil and gas industry. However, it is often the case that the EC directives' requirements for eliminating or controlling exposures to noise and hand-arm vibration (HAV) are not fully implemented in the industry. There are many technical challenges presented by life extension projects. Much of this work may involve significant exposure, but it may also present opportunities to eliminate and control exposures better. Similarly, the construction of new installations provides scope for incorporating good design from the outset.
HSE has encountered recent examples of refit and new build where both engineering design and operational input have been sought. However, the emphasis often remains very much on assessment rather than taking appropriate control actions. Noise and vibration control is not a new science. Noise from process and plant can often be an indicator of (or even mask) plant condition and condition monitoring is now an increasingly sophisticated science. We therefore need to change the perception of this being a ‘health problem’ to being an engineering challenge, for which good engineering design and good practice provide the best solutions. In many cases, this can involve incorporation of simple, well-established principles.
Whilst the major focus of the oil and gas industry is rightly on key issues such as integrity and safe operation, there is still a need to address issues that have serious health implications. Within its broader inspection programme, HSE is examining the way the industry is controlling noise and vibration. It is also looking at good examples of project management where control of noise and vibration has been incorporated. Such examples of good practice provide encouragement and education to others in the industry. This paper describes the approach being taken by HSE in the UK.
Distribution of Ticks from of the Genus Dermacentor (Acari, Ixodidae) in Ukraine
Authors: Akimov I. , Nebogatkin I. 
Published: February 2011

Distribution of Ticks from of the Genus Dermacentor (Acari, Ixodidae) in Ukraine
The northern border of present range of the tick species Dermacentor marginatus is determined on the territory of Ukraine in Volyn, Rivne, Khmelnytsky, Zhytomyr, Kyiv, Cherkasy, Poltava and Sumy oblasts. D. reticulatus species was revealed to be adapted for living in urbanized areas as parasitizing domestic and stray animals, small mammals. It also inhabits shores of artificial reservoirs and occurs in the steppe zone, except for arid areas. D. reticulatus preimaginal stages are found for the first time on birds (Anas platyrhynchos, Sturnus vulgaris, Turdus merula, T. viscivorus).
Developing and Applying a Critical and Transformative Model to Address ESD in Teacher Education
Authors: Kostoulas-Makrakis Nelly 
Published: February 2011

Developing and Applying a Critical and Transformative Model to Address ESD in Teacher EducationA reflective case study approach, including focus interviews, reflective/reflexive journals and analysis of project-based works of 30 pre-service teachers participating in an undergraduate course was employed to investigate the discrepancy between the teachers' constructivist conceptions and the actual practice. The identified discrepancy seemed to be an outcome of the difficulty translating constructivism into teaching practice, but also of the misleading conception of constructivism as a homogeneous philosophy. Through reflective practice, participants were able to deconstruct and reconstruct their theories and practices of teaching in more emancipatory ways addressing issues of education for sustainable development (ESD). This case study helped understand the nature of change process towards teaching and learning for more sustainable futures.
Qualitative Education for Roma Students: A Pedagogical Model for Sustainable Development
Authors: Zaķe Daiga 
Published: February 2011

Qualitative Education for Roma Students: A Pedagogical Model for Sustainable Development
Inclusion of Roma students in general classrooms at an early age (5-7 years) is the focus of this research to study the impact of parent and Roma teacher-assistants' involvement on the learning process of Roma minority students. Though Roma people have inhabited Latvia for centuries, a deeply ingrained prejudice towards Roma is persisting among the population at large, resulting in direct and indirect social discrimination. One of the most odious forms of discrimination against Roma is the practice of consigning Roma students to special schools after ‘their failure’ in the first years of regular elementary schools. Schools, as the primary formal societal institutions that students encounter, have an enormous responsibility in helping to forge a culture of equality, pluralism, tolerance and unity in diversity. This study investigates the development of intercultural learning and anti-bias classroom organisation in order to prevent institutional discrimination and promote the benefits of a culturally heterogeneous society.
Pseudomonas and Pedobacter isolates from King George Island inhibited the growth of foodborne pathogens
Authors: Wong Clemente , Tam Heng , Alias Siti , González Marcelo , González-Rocha Gerardo , Domínguez-Yévenes Mariana 
Published: February 2011

PseudomonasandPedobacterisolates from King George Island inhibited the growth of foodborne pathogensThis report describes the isolation and characterization of bacterial isolates that produce anti-microbial compounds from one of the South Shetland Islands, King George Island, Antarctica. Of a total 2465 bacterial isolates recovered from the soil samples, six (BG5, MTC3, WEK1, WEA1, MA2 and CG21) demonstrated inhibitory effects on the growth of one or more Gram-negative or Gram-positive indicator foodborne pathogens (i.e. Escherichia coli0157:H7,Salmonellaspp.,Klebsiella pneumoniae, Enterobacter cloacae, Vibrio parahaemolyticusandBacillus cereus). Upon examination of their 16S rRNA sequences and biochemical profiles, the six Antarctic bacterial isolates were identified as Gram-negativePedobacter cryoconitis(BG5),Pseudomonas migulae(WEK1),P. corrugata(WEA1) andPseudomonasspp. (MTC3, MA2, and CG21). While inhibitors produced by strains BG5, MTC3 and CG21 were sensitive to protease treatment, those produced by strains WEK1, WEA1, and MA2 were insensitive to catalase, lipase, α-amylase, and protease enzymes. In addtion, the six Antarctic bacterial isolates appeared to be resistant to multiple antibiotics.