bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of single phase i-AlCuFe bulk quasicrystal by spray forming
Authors: Srivastava Vikas Chandra , Uhlenwinkel Volker , Schulz Alwin , Zoch Hans-Werner , Mukhopadhyay Nilay K. , Chowdhury Sandip G.
Published: February 2009

In the present study, an icosahedral single phase bulk quasicrystalline material based on Al62Cu25.5Fe12.5 has been synthesised by a spray forming route. Microstructural characterization showed an average grain size of 10 μm. The oversprayed fine powder showed the presence of β- and λ-phases, whereas, the deposit consited of the fully single phase bulk quasicrystalline material with compositional homogeneity. The hardness and fracture toughness measurements were carried out at different indentation loads of 50–500 g. The hardness values varied in the range 10.4–8.1 GPa and fracture toughness was seen to decrease with increasing load. The varionan of hardness with load, which is known as indentation size effect (ISE), has been established clearly. Fracture toughness value was constant in the load range from 200 to 500 g at 1.2 MPa m1/2. The cracking pattern after indentation at higher load has been observed to be intergranular as well as transgranular. The evolution of the single phase bulk quasicrystalline material has been discussed in light of the unique combination of atomization and deposition process elements in spray forming technique.
Development of an Al–Mn–Be–Cu alloy with improved quasicrystalline forming ability
Authors: Zupanic Franc , Boncina Tonica , Rozman Niko , Anzel Ivan , Grogger Werner , Gspan Christian , Hofer Ferdinand , Markoli Bostjan
Published: February 2009

An Al94Mn2Be2Cu2 cast alloy was developed displaying increased quasicrystalline formation ability at moderate cooling rates. The as-cast microstructure consisted of a mainly icosahedral phase in the Al-matrix. The microstructure remained stable during uniform heating to 580 °C and isothermal annealing at 400 °C. Most of the icosahedral phase was preserved even after 24 h annealing at 500 °C. For that reason, this alloy presents a promising basis for further development of cast Al-alloys containing quasicrystals.
Homometric point sets and inverse problems
Authors: Grimm Uwe , Baake Michael
Published: February 2009

The inverse problem of diffraction theory in essence amounts to the reconstruction of the atomic positions of a solid from its diffraction image. From a mathematical perspective, this is a notoriously difficult problem, even in the idealised situation of perfect diffraction from an infinite structure.

Here, the problem is analysed via the autocorrelation measure of the underlying point set, where two point sets are called homometric when they share the same autocorrelation. For the class of mathematical quasicrystals within a given cut and project scheme, the homometry problem becomes equivalent to Matheron´s covariogram problem, in the sense of determining the window from its covariogram. Although certain uniqueness results are known for convex windows, interesting examples of distinct homometric model sets already emerge in the plane.

The uncertainty level increases in the presence of diffuse scattering. Already in one dimension, a mixed spectrum can be compatible with structures of different entropy. We expand on this example by constructing a family of mixed systems with fixed diffraction image but varying entropy. We also outline how this generalises to higher dimension.
Electronic structures of Al-based transition metal compounds and effective valence of transition elements
Authors: Watanabe Kaoru , Ishii Yasushi
Published: February 2009

Electronic structures of Al-TM (transition metal) compounds with rather simple B2, L12 and A15 structures are studied. Focusing on the energy bands, which are not hybridized strongly with the TM-d bands, we estimate the number of electrons occupying the states below the gap induced by periodic potentials and hence obtain the average number of valence electrons per atom e/a. Although the values of e/a obtained for the different structures are scattered in spite of combination of the same chemical species, these values are obtained if one assumes similar negative values for effective valence of TM. Roles of the interference effect opening the gap in the nearly-free-electron bands are discussed.
Metallographic techniques for the characterization of quasicrystalline phases in aluminium alloys
Authors: Boncina Tonica , Markoli Bostjan , Anzel Ivan , Zupanic Franc
Published: February 2009

Several Al-alloys strengthened by quasicrystalline phases have been developed over the last few years showing the considerable potential for practical application. Therefore there is a strong need for developing new metallographic methods or adapting the traditional ones in order to identify and characterize quasicrystalline phases in a reliable, quick and economical way. This paper describes different techniques: the classical metallographic method, deep etching, particle extraction technique and cross-sectioning using focused ion beam (FIB), and discusses their advantages and disadvantages when identifying quasicrystalline particles. It was discovered that particle extraction techniques are very powerful methods for the identification of phases according to their morphology, and preparation of quality samples for X-ray diffraction (XRD). Transmission electron microscopy (TEM) analyses are also possible provided the extracted particles are thin enough.
Study of quasicrystals obtained from a structural model of icosahedral phases of type F AlPdMn/AlCuFe
Authors: Beauchesne Jean-Tristan , Caillard Daniel , Mompiou Frederic , Ochin Patrick , Quiquandon Marianne , Gratias Denis
Published: February 2009

A recent structural model [1] for the F-type icosahedral phases i-AlPdMn and i-AlCuFe based on the KG cell decomposition [2] of the Mackay clusters has shown that they both enter in an unique model of general composition Al61.8(Pd Ι Cu)21.35(Mn Ι Fe)8.29(Al Ι Fe Ι Mn)4.28(Al Ι Cu)4.28 where (X Ι Y) means X or Y species. Three new alloys satisfying this composition rule, two ternaries Al66.08Cu21.35Mn12.57 and Al70.36Pd21.35Fe8.29 and one quaternary Al66.08Cu21.35Mn8.29Fe4.28 have been prepared by rapid quenching and annealing and studied by X-ray diffraction and electron microscopy. All three phases are quasicrystalline after quench: Al66.08Cu21.35Mn12.57 is decagonal, and the two others are F-icosahedral phases. After annealing, the quaternary alloy transforms into a decagonal phase. The present results are compared to those of previous studies in the litterature of samples with close compositions.
LEED analysis of the surface structure of decagonal Al–Co–Ni using its W-approximant as a model structure
Authors: Pussi Katariina , Diehl Renee D.
Published: February 2009

The analysis of low-energy electron diffraction (LEED) intensities from quasicrystal surfaces requires the use of periodic model structures that contain the same structure features as the quasicrystal. In this paper, we present the analysis of LEED data from 10-fold decagonal Al–Co–Ni using the W approximant structure as the model. A preference was found for an Al-rich termination of the surface, with very little relaxation of the surface planes relative to the bulk structure. This result is similar to the results of an ab inito calculation of a similar surface structure [1]. The results are compared from earlier analyses of the same data using different structure models [2].
Surface study of the (100) and (010) faces of the quasicrystalapproximant Al4(Cr, Fe)
Authors: Smerdon Joseph , Parle Joseph , McGrath Ronan , Bauer Birgitta , Gille Peter
Published: February 2009

Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) results are used to study the pseudo-6-fold nature of the (100) surface of the orthorhombic quasicrystal approximant Al4(Cr, Fe). LEED patterns are also presented from the pseudo-10-fold (010) surface of this material. In each case the results are compared with the known bulk structure of this complex metallic alloy.
Optical response of si-ZnMgHo quasicrystal
Authors: Karpus Vytautas , Babonas Gintautas-Jurgis , Reza Alfonsas , Tumenas Saulius , Arwin Hans , Assmus Wolf , Brühne Stefan
Published: February 2009

The results of room-temperature optical study of single-grain simple icosahedral ZnMgHo quasicrystals are presented. The dielectric function ε (ω) of the quasicrystals was measured by spectroscopic ellipsometry technique in the spectral range of 0.1–7 eV. The si-ZnMgHo optical response is a superposition of the free-electron Drude-type contribution and that of the interband transitions. The experimental ε(ω) spectra are well simulated within a framework of the ‘band structure hypothesis’. The deduced parameters of the si-ZnMgHo electron energy spectrum are close to their values determined previously in an analysis of the si-ZnMgHo photoemission data.
THERAPIE EINES METASTASIERENDEN INSELZELLTUMORS MIT STREPTOZOTOCIN
Authors: Nieschlag E. , Wombacher H. , Kroeger F. J. , Habighorst L.V.
Published: February 2009

A patient with a metastazing functional islet cell tumour suffering from severe hypoglycaemia was treated with streptozotocin. Four intravenous injections of 1.5 g streptozotocin each were administered in 4 to 6 days intervals. After the 4th injection there were no further episodes of hypoglycaemia, parenteral glucose administration could be stopped and blood sugar and plasma insulin, showing concentrations of up to 405 μU/ml before treatment, reached normal levels. The tumours in the pancreas disappeared and the liver metastases decreased in size and number as judged by arteriography.

A hypothesis for the mechanism of action of streptozotocin is proposed. The glucose moiety is considered to facilitate a high affinity to the islet cells whereas the N-methyl-nitrosourea residue serves the active antitumour part of the molecule.
Phenotypes of Mutations in the 5′-UTR of a Limiting Transcription Factor in Aspergillus nidulans Can Be Accounted For by Translational Inhibition and Leaky Scanning
Authors: Oestreicher Nathalie , Scazzocchio Claudio
Published: February 2009

The uaY gene encodes the transcriptional activator of purine catabolism genes in Aspergillus nidulans. uaY12 results in strongly defective growth on purines as nitrogen sources and in strongly diminished transcription of UaY-regulated genes. This mutation introduces an ATG codon 64 bp upstream of the uaY ATG, generating a 68-codon open reading frame (uORFA), overlapping with the uaY ORF. uaY12 revertants fall into three categories:The majority eliminate the aberrant ATG. The growth and transcriptional phenotypes of these revertants are identical to those of the wild type.Two revertants create a stop codon in frame with the uaY12 aberrant ATG, shortening the length of the uORFA, thus uORFA no longer overlaps the uaY ORF. The latter are partial suppressors of the uaY12 mutation, while chain termination suppressors, in turn, suppress this novel phenotype.Two partial suppressors are unlinked to uaY. These two mutations result in a pleiotropic phenotype usually associated with ribosomal proteins.

We hypothesize that uORFA strongly diminishes translation of the uaY ORF and that revertants negate this effect by a number of different mechanisms. The first-AUG rule and the phenomena of translational inhibition and leaky scanning provide a coherent explanation of the results presented in this article.
Outdoor Air Pollution, Genetic Susceptibility, and Asthma Management: Opportunities for Intervention to Reduce the Burden of Asthma
Authors: Gilliland Frank D.
Published: February 2009

Outdoor air pollution at levels occurring in many urban areas around the world has substantial adverse effects on health. Children in general, and children with asthma in particular, are sensitive to the adverse effects of outdoor air pollutants, including ozone, nitrogen oxides, and respirable particulate matter. A growing number of studies also show that children living in environments near traffic have increased risks of new-onset asthma, asthma symptoms, exacerbations, school absences, and asthma-related hospitalizations. The large population of children exposed to high levels of outdoor air pollutants and the substantial risks for adverse health effects present unexploited opportunities to reduce the burden of asthma. Because the evidence indicates significant adverse effects of air pollution at current levels, there is clearly a need to reduce levels of regulated pollutants such as ozone, as well as unregulated pollutants in tailpipe emissions from motor vehicles. Achieving this long-term goal requires the active involvement of physicians and medical providers to ensure that the health of children is at the top of the list of competing priorities for regulatory policy decision-making. Clinical approaches include treatment to control asthma and patient education to reduce adverse effects of the disease. Reduction in exposures also can be approached at a policy level through changes in schools and school bus operations. Beyond clinical and public health approaches to reduce exposure, another strategy to be used before clean air goals are met is to decrease the susceptibility of children to air pollution. Emerging research indicates that dietary supplementation for individuals with low antioxidant levels is one promising approach to reducing susceptibility to air pollution. A second approach involves induction of enzymatic antioxidant defenses, especially for individuals with at-risk genetic variants of key antioxidant enzymes.
The 2007 National Asthma Education and Prevention Program Asthma Guidelines: Accelerating Their Implementation and Facilitating Their Impact on Children With Asthma
Authors: Gupta Ruchi S. , Weiss Kevin B.
Published: February 2009

Nearly 2 decades have elapsed since the National Center for Health Statistics raised concerns regarding the trends in increasing asthma prevalence. Additional research highlighted the large racial disparities and geographic variations in asthma morbidity and mortality rates. Although there was little national consensus on the care of children with asthma at the time, there were improvements in the understanding of the mechanisms and treatment of asthma. It was in this context that the National Heart, Lung, and Blood Institute launched the National Asthma Education and Prevention Program, which convened its first panel of experts to create the national consensus clinical practice guidelines on the treatment of asthma. More than 15 years have passed since the publication of those first guidelines and, in August 2007, the National Heart, Lung, and Blood Institute released its newest updates, which are the product of the National Asthma Education and Prevention Program third expert panel. The release of the updated guidelines serves as an occasion to examine important issues regarding the dissemination and clinical implementation of National Asthma Education and Prevention Program guidelines. The goals of this report are to examine the adoption of earlier versions of the National Asthma Education and Prevention Program guidelines and to suggest opportunities for rapid adoption of the newly released guidelines.
A császárkori római szarkofágok Erós-„melléktémái” és a poliszémikus kontempláció
Authors: Berczelly László
Published: February 2009

A
bevezetőben a szerző összefoglalja a római szarkofágok ikonográfiai kutatásának
legfontosabb problémáit és eredményeit. A képnyelv könnyebb megértése kedvé_
The Differential Efficacy of Pemetrexed According to NSCLC Histology: A Review of Two Phase III Studies
Authors: Scagliotti Giorgio , Hanna Nasser , Fossella Frank , Sugarman Katherine , Blatter Johannes , Peterson Patrick , Simms Lorinda , Shepherd Frances A.
Published: February 2009

Background.

Recent studies of pemetrexed have identified a predictive role for non-small cell lung cancer (NSCLC) histology. We further reviewed the differential efficacy of pemetrexed according to histology in two large, phase III NSCLC trials.

Methods.

One study tested pemetrexed versus docetaxel in previously treated patients (n = 571) and the other tested cisplatin plus pemetrexed versus cisplatin plus gemcitabine in chemotherapy-naive patients (n = 1,725) with advanced NSCLC. Cox proportional hazard models were used to test for covariate-adjusted treatment-by-histology interactions (THIs) for overall survival (OS) and progression-free survival (PFS). For each histologic subgroup, the Kaplan–Meier method was used to estimate unadjusted within-arm medians, and Cox models were used to estimate covariate-adjusted between-arm hazard ratios (HRs).

Results.

In both studies, treatment arms were well balanced for histology. THIs were statistically significant (p < .005) for both OS and PFS. Nonsquamous patients treated with pemetrexed-based therapy experienced longer survival than the comparators (HR, 0.78 and 0.84, respectively), whereas squamous patients had shorter survival (HR, 1.56 and 1.23, respectively). Whereas the efficacy of pemetrexed regimens differed according to histology, it did not differ for docetaxel or for cisplatin plus gemcitabine. Pemetrexed was well tolerated across histologic groups.

Conclusions.

The consistency of these results across studies confirms the predictive effect of histology for pemetrexed and the survival advantage for pemetrexed in patients with nonsquamous histology. These analyses suggest pemetrexed should not be recommended for the treatment of squamous cell carcinoma, but, because of efficacy and safety advantages, pemetrexed may be preferable to other agents for treatment of patients with nonsquamous NSCLC.
Reclamation of a slurry pond in Singapore
Authors: Chu J. , Bo M. W. , Arulrajah A.
Published: February 2009

A case study for the reclamation of a slurry pond as part of an offshore reclamation project in Singapore is presented in this paper. The slurry pond covered an area of 180 ha. The slurry in the pond was recently deposited ultra-soft high-plasticity clay. The water content of the slurry was more than 120% and the undrained shear strength was less than 8 kPa. The reclamation was first carried out by spreading sand fill in thin layers 20 cm thick using a specially designed sand spreader. The filling speed was carefully controlled to allow the slurry to be consolidated before more fill could be placed. Despite the precautions a failure occurred, in the form of mud bursting. As a remedial measure, geotextile sheets were used to cover a total area of 630 000 m2 before more sand fill was placed. After the completion of fill placement, fill surcharge and prefabricated vertical drains (PVDs) were used to improve and accelerate the consolidation of the slurry. As the performance of PVDs would deteriorate after they had undergone large deformation, they were installed in two passes. In the first pass PVDs were inserted with a square grid spacing of 2·0 m. After nearly 1·5 m of settlement had taken place, the second pass of PVDs with the same spacing was installed at the centre of the square grid of the PVDs installed in the first pass. After nearly 4 years of consolidation, the top of the slurry had settled more than 3 m. The undrained shear strength had also increased substantially. Therefore the use of PVDs for the improvement of the ultra-soft slurry was successful in this project.
Biological in situ reinforcement of sand in near-shore areas
Authors: Van der Ruyt M. , van der Zon W.
Published: February 2009

BioGrout is the process by which bacteria control the precipitation of calcium carbonate while consuming supplied reagents. By controlling the amount of reagents, the amount of calcium carbonate and thus the strength of the reinforced sand body can be engineered. The main advantage of BioGrout is that soil (or sand) can be strengthened, without interfering with the hydraulics of the treated soil and without excavation or replacement. The result is a stiffer sand layer with a higher bearing capacity, higher resistance against erosion and higher resistance against shear forces. The higher strength enables can protect under water slopes against liquefaction and breaching but can also protect dunes or river bends against erosion, reduce costs for wave protection measures (stone protection) etc.
Making a case for investment in the public realm
Authors: Buchanan P. , Gay N.
Published: February 2009

High-quality urban realm generates benefits to pedestrians in terms of improved walking experience and contributes to the socio-economic vitality of streets and neighbourhoods. However, it is very difficult to value and quantify those benefits. Historically, transport appraisal guidance has only allowed for the quantification of safety and time-saving benefits to pedestrians, which represent a small portion of benefits arising from public realm schemes. There are two main approaches to valuing the benefits to be gained from improved urban realm: the bottom-up approach of valuing benefits to individuals through stated preference (SP) and a top-to-bottom approach using revealed preference (RP). A method for quantifying user benefits using SP surveys has been developed. SP, however, only represents a partial valuation of benefits (not accounting for wider socio-economic benefits) and the values derived from SP surveys are subject to uncertainty. An alternative approach, using RP, measured the impact of public realm quality on market prices (retail rents and residential property prices). Although the results from this work showed a link between the quality of public realm and market prices, more research is needed to assess and value the benefits of public realm schemes.
Control effort exacerbates invasive‐species problem
Authors: Rinella Matthew J. , Maxwell Bruce D. , Fay Peter K. , Weaver Theodore , Sheley Roger L.
Published: February 2009

Ecosystem managers face a difficult decision when managing invasive species. If they use aggressive practices to reduce invader abundances, they will likely reduce invaders' competitive impacts on natives. But it is often difficult or impossible to reduce invaders without damaging natives. So a critical question becomes: Which is worse for native biota, invaders or things done to control invaders? We attempted to answer this question for a common scenario. We studied several grassland natives exhibiting long‐term coexistence with an invader and asked how aggressive management (herbicide use) affected the natives. Whether or not grazing was excluded, one‐time herbicide use made two native forbs exceedingly rare for our entire 16‐year study period. Herbicide also made several other native forbs rare, but only when grazing was excluded, and there is evidence that the dominant invader became more abundant in response to the decreases in native‐forb abundances. Throughout the world, terrestrial and aquatic ecosystems are receiving herbicide applications for exotic‐species control. Some of the applications are doubtless warranted because they target small invader patches or larger areas with virtually no remaining natives. However, other herbicide applications occur where large native populations occur, and our data suggest that these applications can be ill advised. Our cautionary tale is told using an herbicide‐treated grassland, but our results should be considered wherever invasive‐species management damages native species.
Toxicity of orimulsion-400® to early life stages of atlantic herring (Clupea harengus) and mummichog (Fundulus heteroclitus)
Authors: Boudreau Monica , Sweezey Michael J. , Lee Kenneth , Hodson Peter V. , Courtenay Simon C.
Published: February 2009

The toxicity of Orimulsion-400® (PDVSA-BITOR), an emulsion of 70% bitumen in 30% water, was tested during the embryonic development of Atlantic herring (Clupea harengus) and mummichog (Fundulus heteroclitus) in duplicate experiments. Air injection and different salinities were included in the herring assays to examine their effects on Orimulsion-400 toxicity. Water-accommodated fractions (WAFs) of no. 6 fuel oil were tested in the mummichog assays to compare Orimulsion-400 toxicity with that of a heavy fuel oil. Concentrations of Orimulsion-400 as low as 0.001% (v/v) were harmful to both species. In herring, the more sensitive of the two species, this concentration produced 100% abnormal larvae. Similar abnormalities, including pericardial edema and spinal deformities, the same signs of toxicity caused by heavy fuel oils and polycyclic aromatic hydrocarbons (PAHs), were produced in both herring and mummichog. Fish exposed to Orimulsion-400 also suffered from increased mortality, reduced heart rates, premature hatch, and reduced lengths compared to control fish. Orimulsion-400 was approximately 300-fold more toxic than the WAFs of no. 6 fuel oil. Salinity had few clear effects on Orimulsion-400 toxicity, but aeration of test solutions greatly reduced toxicity by causing bitumen to coalesce and float. Aeration also removed toxic chemicals such as PAHs. The present study suggests that in the event of a spill, Orimulsion-400 could impair fish recruitment, but that strong wave action would reduce toxicity by accelerating the removal of emulsified bitumen from the water column.
A Multidomain Approach to Multiscale Compositional Reservoir Simulation
Authors: Al-Matrouk Mohammed F. , Al-Kobaisi Mohammed , Kazemi Hossein , Ozkan Erdal
Published: February 2009

This paper presents a multidomain (MD) computational approach to multiscale (MS) compositional reservoir simulation amenable to parallel processing. The main objective is to minimize the upscaling process and preserve the pertinent flow characteristics of the fine-scale geological features of the reservoir. The preservation of the fine-scale reservoir characteristics yields higher-accuracy solution compared to an upscaled model.

The computing algorithm involves breaking down the fine-grid (FG) computing mesh into an underlying coarse-grid (CG) subdomain. Unlike other MS techniques, the CG subdomain only serves as an assemblage of the FG cells and not as a computational CG overlaying the FG cells. The flow equations are then restructured into a global pressure equation which is solved on the FG using a large time step without solving for the compositions, saturations, etc. The convergence tolerance for the global pressure solution is soft (no iterations) to reduce computing time. The pressure solution is then used to calculate the molar flux of components only at the FG boundaries of the CG subdomain cells. Finally, each CG subdomain subject to its boundary conditions is solved independently using a smaller time step to compute cell pressures, compositions, and phase saturations. This procedure is amenable to parallel processing.

This MS scheme was applied to time domain, in which the global pressure solution is obtained with a larger time step than in the local FG solution. This means that the molar flux boundary condition at the CG subdomain boundaries is not updated every time step, thus, buying additional computational advantage. This new technique was tested on several volatile oil and gas-condensate systems and excellent agreement was obtained with FG simulation with about 60% reduction in computing time using a single processor. Much greater time reduction is expected in a multi processing environment.
Stochastic Inversion for Reservoir Properties Using Parallel Learning-Based VFSA and Pilot Point Parameterization
Authors: Jin Long , Stoffa Paul L. , Sen Mrinal K.
Published: February 2009

Joint inversion of flow and seismic data for reservoir parameters is a challenging task in that these disparate datasets are sensitive to different physics and model resolutions for the forward problem. The inverse problem is highly non-linear introducing additional complexity. To overcome some of these challenges, we developed a global optimization method based on very fast simulated annealing (VFSA) and a multi-resolution model parameterization scheme. The choice of proposal distribution for sampling the parameter space and the time consuming of reservoir modeling are two critical issues which need to be resolved. Here, we propose a new parallel learning-based VFSA to address these issues. The key idea behind this method is that at any iteration, the previously sampled models are saved and used as guides in subsequent search resulting in an increased effieciency in our search speed. Parallel computing is used to search a much wider model space without increasing the computing time.

Our new method works as follows: (1) the Cauchy distribution is used as the proposal distribution in the beginning; (2) parallel computing is used to sample the parameter space in multiple chains each running at a different temperature; (3) at certain iterations, we collect all the sampled models from the previous parallel runs and compute the binned probability distribution of the model parameters; (4) new proposal distribution is formed by combining the computed probabilityr distribution and Cauchy distribution for every parameter; (5) parallel sampling using the new proposal distribution; (6) collection of all the models and computation of posterior distribution.

The results from the synthetic examples reveal that our method is able to obtain reasonable descriptions of the reservoir by combining the global optimization and multi-resolution parameterization. Our new parallel learning-based VFSA shows better performance compared with a conventional method in terms of accuracy.
Parallel Numerical Reservoir Simulations of Non-Isothermal Compositional Flow and Chemistry
Authors: Delshad M. , Thomas S. G. , Wheeler M. F.
Published: February 2009

This paper describes an efficient numerical scheme for non-isothermal compositional flow coupled to chemistry. An iterative IMPEC method is applied to solve the flow problem using a volume balance convergence criterion. A backward Euler mixed FEM with lowest order RT0 elements is applied to solve the pressure equation and a component local mass preserving explicit scheme is used to update concentrations. Chemical reactions are solved using explicit Runge-Kutta ODE integration schemes. A higher order Godunov method and a backward Euler mixed FEM are applied for thermal advection and conduction, respectively, in a time-split scheme.

One of the major applications of the method is in the modeling of field scale CO2 sequestration as an EOR process or for containment in deep saline aquifers where chemical reactions and temperature variations may have an impact on the flow and transport of CO2. Leakage patterns when CO2 is injected near leaky abandoned wells, the displacement of methane from depleted gas reservoirs and accurate modeling of geochemical reactions involving injected CO2 are other applications of interest.

Results of a benchmark problem in multiphase flow with several hydrocarbon components in formations with highly heterogeneous permeability on very fine grids, as well as a large scale parallel implementation of modeling CO2 sequestration are presented to justify the practical use of the model. A parallel efficiency of about 80% was observed on upto 512 cores in the benchmark study. Results from a problem simulating injection of CO2 in deep aquifers including non-isothermal and chemical effects are also presented. The results indicate a good agreement of the solutions with published data where available.

Numerical modeling and simulation of CO2 sequestration plays a major role in future site selections and in designing storage facilities for effective CO2 containment. The main contribution of this paper lies in providing a parallel and efficient method of simulating challenging compositional flow problems such as in the study of CO2 sequestration as well as flow coupled to thermal and geochemical effects.
An Iterative Algorithm for Generating Constrained Voronoi Grids
Authors: Katzmayr Markus , Ganzer Leonhard
Published: February 2009

In general, the purpose of a simulation is to mimic a real system in order to study its behavior. Among the first steps in a simulation study is the proper definition of the spatial discretization. This abstraction process of the space domain produces the simulation model and is essential for the result of the simulation.

A new approach for the simulation of faulted hydrocarbon reservoirs is proposed. The described algorithm iteratively generates a constrained Voronoi grid suitable for two-point flux approximation schemes. The algorithm is based on a Delaunay triangulation and is characterized by its robustness, efficiency and the iterative modeling approach. Initially, a Delaunay triangulated mesh is calculated for a given point distribution. Using the triangulated mesh, the proper Voronoi grid is derived. Constraints (faults, pinch-outs, boundaries) are aligned sequentially on the derived Voronoi cell and integrated into the Delaunay mesh. The alignment is necessary to ensure that the use of two-point flux approximation methods on the generated reservoir grid model is correct. The higher the resolution of the point distribution in the area of the constraint, the better the aligned constraint matches the actual constraint. Finally, all Voronoi cells touching the integrated constraints are reconstructed using the Delaunay mesh. Similar to the insertion of new constraints, local grid refinements or model elements can be added without reconstructing the entire model. All modifications of the reservoir model result in local grid adjustments.

The runtime complexity of the algorithm depends on constructing the underlying Delaunay mesh and can be estimated as O(n log n) plus some overhead O(n) for deriving the Voronoi grid.

This new approach reduces the construction and updating times for reservoir grid models considerably and results in grid models ranging from structured, Cartesian-type of grid to high complex unstructured models depending on the original distribution of grid points.
Efficient and Accurate Reservoir Modeling Using Adaptive Gridding with Global Scale Up
Authors: Branets Larisa V. , Ghai Sartaj S. , Lyons Stephen L. , Wu Xiao-Hui
Published: February 2009

An accurate and efficient reservoir modeling process is essential for developing and producing hydrocarbon reserves, especially from unconventional resources. In this paper, we address some of the main challenges associated with modeling complex reservoir geometry and heterogeneous reservoir properties. We present recently developed techniques for adaptively constrained 2.5D Voronoi grid generation and for generic global flow-based scale-up. Our novel gridding approach is based on a new constrained Delaunay triangulation algorithm and a rigorous procedure of constructing a Voronoi grid that conforms to piecewise linear constraints. These gridding approaches allow us to generate 2.5D Voronoi grids that precisely honor small faults, intersections of multiple faults, and intersections of faults at sharp angles, as well as adapt the grid cell sizes to a specified density function. By precisely representing geologic structures in our simulation grid and by accurately scaling up fine-scale geologic properties, we improve the consistency between our geologic descriptions and reservoir simulation models, leading to more accurate simulation results.

Numerical examples are provided to demonstrate the techniques and the advantages (both in efficiency and accuracy) of using adaptive gridding with global scale-up.
Development of a Reservoir Simulator for Souring Predictions
Authors: Farhadinia M. A. , Bryant S. L. , Sepehrnoori K. , Delshad M.
Published: February 2009

During the last two decades, several simple models have been developed to predict the onset of reservoir souring in seawater injected reservoirs. The key mechanism to generate hydrogen sulfide is a biological reaction between sulfate in the injection water and volatile fatty acids in the formation water in the presence of sulfate reducing bacteria (SRB). The produced hydrogen sulfide interacts with rock and partitions between oil and water phases. Comparison of field data with reservoir souring model predictions often shows inconsistent results. We present the development of a comprehensive reservoir souring model in a chemical flooding simulator that accounts for these mechanisms.

Being able to estimate the likelihood and timing of the onset of H2S production would permit more realistic assessments of project economics. We incorporated mechanisms of generation and transportation of H2S in porous media to develop a reservoir souring simulator to predict the onset of souring in oil reservoirs.

We implemented a general souring model in a 3D finite difference compositional non-isothermal reservoir simulator. The results indicate that depending on the type of SRB, the temperature propagation in the formation determines the onset of biological reactions and consequently, the generation of different hydrogen sulfide concentrations. The lag in the temperature front with respect to the injection front can cause a delay in the observed souring if the temperature is not favorable for SRB activation.

A predictive model would enable operators to make better decisions for remedial actions to either prevent souring or to mitigate its impact. The developed finite difference simulator is 3D and accurately accounts for variation and impact of in-situ concentrations, temperature, pressure, and reservoir heterogeneity on H2S transport and production.
Feedback Controllers for the Simulation of Field Processes
Authors: Guyaguler B. , Papadopoulos A. T. , Philpot J. A.
Published: February 2009

Control systems with feedback controllers are useful in reservoir simulation as they enable the maintenance of desired operating conditions of a field. This in turn helps establish the value of implementing automated mechanisms in the field, and also in determining long term field operating strategies. A generic controller framework is constructed within a reservoir simulator that enables the usage of different kinds of controller algorithms for managing a variety of field processes. In this study, three field processes are considered. First, average pressure within a reservoir region is maintained by adjusting the voidage replacement ratio between a group of injectors and producers. Second, control systems are used for the prevention of gas/water coning for single and multiple wells. Finally, the average temperature within a reservoir region is maintained at a critical value by controlling flow into the formation, so as to operate with the desired mobility of heavy-oil. Traditional Proportional, Integral, Derivative (PID) controllers, as well as linear and nonlinear fuzzy controllers are considered. The advantages and disadvantages of the approaches are discussed. Tuning control systems is a difficult process in practice. Several methods for tuning the parameters of these controllers are investigated, and rule-of-thumb values are suggested in this study. Synthetic and real reservoir models are used.
Experience With Numerical Stability, Formulation, and Parallel Efficiency of Adaptive Implicit Methods
Authors: Lu P. , Shaw J. S. , Eccles T. K. , Mishev I. D. , Beckner B. L.
Published: February 2009

The availability of multi-core CPUs for personal computers makes desktop parallel computing a reality. Parallel computing for reservoir simulation creates the opportunity for significant run time reduction but also introduces additional technical challenges, particularly in the areas of load balancing and general algorithmic robustness.

In this paper we will discuss our experience with the Adaptive Implicit Method (AIM) in parallel desktop computing environments, with ExxonMobil's numerical reservoir simulator, EMpowerTM, focusing on the following areas: A highly efficient and robust parallel partition of the fully unstructured grids for modeling large and complex reservoirsAdaptive Implicit Method (AIM) for a high-level of numerical stability with significant run-time speed-up and memory footprint reductionUnique load balancing challenges arising from integration between shared-memory based parallel computing, unstructured grids, and adaptive implicit methods

We will also describe experiences with real models and discuss mechanisms for addressing problems encountered and demonstrate that we can achieve a 3~4 time speedup over serial runs without AIM on real field cases using quad-core desktop machines.
Closed-Loop Reservoir Management
Authors: Jansen J. D. , Douma S. D. , Brouwer D. R. , Van den Hof P. M. J. , Bosgra O. H. , Heemink A. W.
Published: February 2009

Closed-loop reservoir management is a combination of model-based optimization and data assimilation (computer-assisted history matching), also referred to as ‘real-time reservoir management’, ‘smart reservoir management’ or ‘closed-loop optimization’. The aim is to maximize reservoir performance, in terms of recovery or financial measures, over the life of the reservoir by changing reservoir management from a periodic to a near-continuous process. The key sources of inspiration for our work are measurement and control theory as used in the process industry and data assimilation techniques as used in meteorology and oceanography. We present results of a numerical example to illustrate the scope for closed-loop water flooding using real-time production data under uncertain reservoir conditions. The example concerns a 12-well water flood in a channelized reservoir. Optimization was performed using a reservoir simulator with functionality for adjoint-based life cycle optimization under rate and pressure constraints. Data assimilation was performed using the ensemble Kalman filter. Applying an optimization frequency of respectively once per 4 years, once per 2 years, once per year and once per 30 days resulted in an increase of net present value (NPV) with 6.68, 8.29, 8.30 and 8.71% compared to a conventional reactive control strategy. Moreover, the results for the 30-day cycle were very close (0.15% lower NPV) to those obtained by open-loop optimization using the ‘true’ reservoir model. We illustrate that for closed-loop reservoir management with a fixed well configuration, the use of considerably different reservoir models may lead to near-identical results in terms of NPV. This implies that in such cases the essential information may be represented with a much less complex model than suggested by the large number of grid blocks in typical reservoir models. We also illustrate that the optimal rates and pressures as obtained by open- or closed-loop optimization are often too irregular to be practically applicable. Fortunately, just as is the case for the data assimilation problem, the flooding optimization problem usually contains many more control variables than necessary, allowing for optimization of long-term reservoir performance while maintaining freedom to perform short-term production optimization.
Efficient Parallel Reservoir Simulation Using Multicore Architectures
Authors: Khait M. L.
Published: February 2009

Modern reservoir simulation of complex physical processes for highly detailed models needs a lot of computational power. Constrained Pressure Residual (CPR) – based preconditioner for linear solver are the best in terms of performance and robustness for reservoir simulation. From another side the most advanced processors are based on multi-core architectures, which allow for efficient parallel processing with extremely low cost of memory-processor communication. The work was focused on adaptation of CPR algorithms for multi-core architectures with help of OpenMP technology, as well as parallelization the rest of simulation code. This work was done based on Stanford's General Purpose Research Simulator (GPRS). The two-stage CPR preconditioner where the first stage involves formulating and solving a global pressure system, and the second stage requires application of a simple preconditioner, but on the full Jacobian, was completely parallelized. One of the most challenging issues was parallelization of ILU(0) which implies second stage of preconditioning. One of approaches of parallel ILU(0) based on domain decomposition was formulated and tested using challenging compositional simulation problems with highly detailed models. The results demonstrate good scalability of this parallel ILU(0) approach for SPE 10 compositional model.
Automatic Well Placement Optimization in a Channelized Turbidite Reservoir Using Adjoint Based Sensitivities
Authors: Castiñeira David , Alpak Faruk O. , Hohl Detlef
Published: February 2009

Economic constraints impose stringent limits on the number of wells that can be drilled in deepwater developments. Thus, optimal placement and operation of wells have a major impact on the project rewards. Well-placement in deepwater developments is a challenging optimization problem. Manual approaches to its solution can be cumbersome even with good use of engineering judgment: (a) There often exist many combinations of well locations subject to investigation; (b) There is need to optimize operational constraints for every well-placement scenario; (c) The optimization process has to be repeated for a variety of geologic realizations; (d) Presence of complex sub-seismic geologic architecture may render workflows that solely rely on seismic data obsolete. We developed an adjoint-based optimization algorithm that rapidly identifies alternative optimal well-placement scenarios for a given geologic realization. Adjoint-based gradients approximate the sensitivities of a suitable objective function with respect to well locations. These sensitivities guide the iterative search with improving directions that progressively maximize the ultimate recovery. The main advantage of the adjoint method is that it provides sensitivities with only one forward (reservoir) and one backward (adjoint) simulation, rendering computational costs affordable for field applications. The adjoint method in our implementation operates in local search mode.

Our algorithm is applied to two different geologically complex channelized turbidite reservoirs to identify alternative optimal locations for a new injector-producer pair given existing operational and well constraints. Ensuing results demonstrate that the adjoint-based sensitivities can be effectively used to find optimal well locations. In the field simulation models, the optimization derived well locations lead to a higher ultimate oil recovery compared to a manual optimization approach. The algorithm yields multiple alternative well-placement scenarios within a shorter amount of time compared to a single optimal location found through manual optimization.