bluuebunny/crossref_metadata_2025 huggingface dataset:
Regressing the Size and Cost of Turbulent Cavity Flow Simulations
Authors: Rona A. , Monti M.
Published: July 2011

A successful model of high Reynolds number cavity flows involves reproducing the flow physics with adequate accuracy, given the available computational resources. The process of planning high Reynolds number cavity flow simulations is systematically reviewed to extract the dependence of different programmer's choices on the CFD mesh size and on the cost of the computation.

This process has been broken down into five phases: i) description of the problem in the continuous domain, ii) problem order reduction by turbulence modelling, iii) discretization in space and time, iv) integration of the governing equations, v) costing the numerical operations of the flow solver. This paper examines the influence of each phase on the spectral width and the grid density, which are the key CFD indicators that determine the cost of the computation.

A dimensional analysis was conducted to separate the effects of the geometry of the enclosure, the boundary layer resolution, the turbulence model, and the numerical scheme order of accuracy. Regression analysis on the non-dimensional groups of published cavity CFD simulations determined the range of practical values used by current state-of-the-art computations. This analysis is a useful tool for obtaining design trade-offs by a multivariate optimization in cavity flow CFD and for estimating the order of magnitude of the computational resources required by the simulations.
Recursive Algorithm for the Effective Impedance of Multilayered Acoustic Losses Media
Authors: Ali M.G.S.
Published: July 2011

This paper describes a rapid algorithm for effective impedance in multilayered media. The layers are considered losses and have parallel interfaces. Recursive equations are developed and introduced that enable to calculate the effective impedance in compartments composed of any arbitrary number of layers. The calculations are carried out through an iterative process. Several important influence factors, that affect the multilayer acoustic absorber, are discussed. A simple algorithm is proposed, which allows to obtain qualitative knowledge of the behaviour of the frequency band with layer parameters. This technique can be used in different applications of ultrasonic techniques.
Star Colouring Problem: The DNA Solution
Authors: Sethuraman G. , Kavitha J.
Published: July 2011

In this paper, a DNA based computing model for solving the star coloring problem is proposed. This model shows how to use DNA strands to construct solution space of molecules for the star coloring problem and how to apply the DNA algorithm to solve the star coloring problem using biological operations. The algorithm is highly parallel and has satisfactory fidelity. The time complexity of the algorithm is O (n2), where n is the number of vertices of the graph.
Security Evaluation of Passwords Used on Internet
Authors: Hub Miloslav , Capek Jan
Published: July 2011

This paper presents results of empirical study of passwords really used on internet. These passwords were obtained during two data acquisitions in three years period. In this paper a method for the evaluation of password security against a dictionary attack and a brute force attack is suggested and used for security evaluation of these passwords. The method is based on a mathematical model and a simulation of dictionary attack and a brute force attack. In the paper trends of password selecting are identified and expected progress is outlined. Simultaneously truly used passwords are investigated by statistic methods.
Design and Implementation of Synchronized Collaborative System upon Heterogeneous CAD Systems
Authors: Dou Wanfeng , Song Xiaodong , Zhang Xiaoyong
Published: July 2011

The synchronized collaborative design within heterogeneous CAD systems becomes a significant challenge because of the great difference in the modeling operations and underground data structures between different CAD systems. This paper first proposes a collaborative architecture with heterogeneous CAD systems, which is composed of CADAdapter component and CoCADMiddleware component. The CADAdapter is responsible of capturing of local operation commands and replaying of remote operations, and the CoCADMiddleware takes charge of operation translation of operation commands between different CAD systems. In order to accomplish the translation of system modeling command (SMC) between different CAD systems, a description of neutral modeling command (NMC) is presented to represent these neutral operation commands. By means of this representation the transformation algorithms of operation commands from different CAD systems, SMC-to-NMC module and NMC-to-SMC module, arepresented. The design and implementation of a prototype of synchronized collaborative design system is discussed based on two common CAD systems UG NX3.0 and SolidWorks 2004 with their APIs and VC++.
Generating Approximate Inverse Preconditioners for Sparse Matrices Using CUDA and GPGPU
Authors: Xu Shiming , Xue Wei , Wang Ke , Lin Hai Xiang
Published: July 2011

The problem of numerical solution of sparse matrix-based linear systems arises from many scientific applications. Iterative solvers and corresponding preconditioning techniques are usually adopted. Due to the the irregularity in memory access patterns and undeterministic branching behavior of sparse matrix-based algorithms, they present unique problems for emerging GPU-based platforms.

This paper discusses the techniques associated with applying GP-GPU and CUDA to the generation of right-looking approximate inverse preconditioners (AINV) and preconditioned GMRES based on them. Parallel algorithms are designed for generating AINV preconditioners with predefined sparsity pattern or dynamic fill-in control themes. Detailed complexity analysis is provided for dynamic fill-in control in preconditioners. Shared Memory-based optimization yield 200% speedup in the sparse vector inner products and sparse vector updates; while overall speedup compared with parallel CPU-based implementations are 3 times and 6 times, respectively. The preconditioned GMRES iteration based on AINV witnessed 7 to 9 times speedup, due to the high efficiency of matrix-vector product based preconditioning. The developed techniques can also be applied to other Krylov solvers and preconditioners.
A Note on Solvability Conditions for Multiple Objectives Linear Programming (MOLP) Problems
Authors: Tantawy S.F.
Published: July 2011

This paper investigates the advantages of using a simple linear programming problem with one unknown to show that whether the given multiple objectives linear programming (MOLP) problems is solvable or not. This kind of investigation is based mainly on both of feasibility and efficiency characterization of the (MOLP) problem. Our goal of this investigation is to help the analyst of better understanding of the nature and the theory of the given problem under consideration. Some illustrative examples is given to clarify this investigation study.
A New Approach in Financial Modelling with the Aid of Artificial Neural Networks
Authors: Christakis Nicholas , Barbaris Vasileios , Spentzos Agis
Published: July 2011

In recent years there has been significant interest in Artificial Neural Networks (ANNs) and their suitability for the solution of many real-world problems. When simulating complex systems which display highly nonlinear behaviour, traditional methods prove insufficient either due to their oversimplified problem description or due to the lack of available computer resources. ANNs have been shown to be quite successful when applied to such problems whose dynamics may not be explicitly understood. The use of ANNs has become more widespread with increasing computing processing power. In this work we present a brief overview of the ANN model developed and its validation and concentrate on specific applications in the area of financial modelling, where the network manages to reconstruct with quite high accuracy the behaviour of a very complex problem, such as the prediction of the performance of a bank stock. This constitutes the first step towards the creation of a framework which enables mathematical models to benefit from the ability of ANNs to resolve complex trends.
RNase P: At last, the key finds its lock
Authors: Masquida Benoît , Westhof Eric
Published: July 2011

Apart from the ribosome, the crystal structure of the bacterial RNase P in complex with a tRNA, reported by Reiter and colleagues recently, constitutes the first example of a multiple turnover RNA enzyme. Except in rare exceptions, RNase P is ubiquitous and, like the ribosome, is older than the initial branch point of the phylogenetic tree. Importantly, the structure shows how the RNA and the protein moieties cooperate to process the pre-tRNA substrates. The catalytic site comprises some critical RNA residues spread over the secondary structure but gathered in a compact volume next to the protein, which helps recognize and orient the substrate. The discussion here outlines some important aspects of that crystal structure, some of which could apply to RNA molecules in general.
Toxicity of Alzheimer's disease-associated Aβ peptide is ameliorated in a Drosophila model by tight control of zinc and copper availability
Authors: Hua Haiqing , Münter Lisa , Harmeier Anja , Georgiev Oleg , Multhaup Gerd , Schaffner Walter
Published: July 2011

Amyloid plaques consisting of aggregated Aβ peptide are a hallmark of Alzheimer's disease. Among the different forms of Aβ, the one of 42aa length (Aβ42) is most aggregation-prone and also the most neurotoxic. We find that eye-specific expression of human Aβ42 in Drosophila results in a degeneration of eye structures that progresses with age. Dietary supplements of zinc or copper ions exacerbate eye damage. Positive effects are seen with zinc/copper chelators, or with elevated expression of MTF-1, a transcription factor with a key role in metal homeostasis and detoxification, or with human or fly transgenes encoding metallothioneins, metal scavenger proteins. These results show that a tight control of zinc and copper availability can minimize cellular damage associated with Aβ42 expression.
Results of the recalibration of creatinine measurement with the modular Beckman Coulter® Jaffe creatinine method
Authors: Fillée Catherine , Vranken Guido , Othmane Myriam , Philippe Marianne , Allaeys Jean-Michel , Courbe Anne , Ruelle Jean-Luc , Peeters Rudy
Published: July 2011

Serum creatinine is important for detecting the beginning of a decline in kidney function. The Beckman Coulter Jaffe reagents for measuring creatinine have been standardized to the internationally accepted reference method: isotope dilution mass spectrometry (IDMS). The impact of this recalibration on the Beckman Coulter

Recalibrated Jaffe (calibrator set points IDMS traceable) and classic National Institute of Standards and Technology (NIST) creatinine methods (traceable to NIST 914a) were compared with an enzymatic method (Sentinel, traceable to NIST SRM 967). All measurements were performed on Synchron DxC 800 systems. Imprecision of the routine methods was studied using the Clinical and Laboratory Standards Institute (CLSI) protocols and laboratory quality survey. Thirteen plasma pools, with concentrations <354 μmol/L, were analyzed with a gas chromatography isotope dilution mass spectrometry (GC-IDMS) method and routine methods. Total error of 8.2% based on biological variability, set on the GC-IDMS values and acceptance criteria (bias <5%, imprecision <8% at concentrations ≥88.4 μmol/L and a maximum 10% increase in the relative error of estimated glomerular filtration rate (eGFR) of the National Kidney Disease Educational Program (NKDEP) were used for evaluating analytical performance of the routine methods studied.

After recalibration of the Jaffe method, median bias (μmol/L) decreased from 12.4 (95% CI: 9.1–21.2) to 7.3 (95% CI: 1.5–10.5). Imprecision of the Jaffe method is in agreement with the claim of the manufacturer, namely <9 μmol/L or <3% below or above 292 μmol/L. Below creatinine of 88.4 μmol/L, imprecision of the recalibrated Jaffe and enzymatic methods is between 4.1% and 6.9%, and 5.0% and 7.1%, respectively, and significantly different (p=0.02 for both the Jaffe and enzymatic methods) from the goal, based on biological variability, of 2.7%. For the adult pools, all recalibrated Jaffe and enzymatic results fall within the total error of 8.2%. In the pediatric samples, one-third of the recalibrated Jaffe and three of the six enzymatic results fall within this total error goal.

Recalibration significantly reduced bias of the Jaffe method. For pediatric samples, recalibrated Jaffe results do not comply with either the imprecision goal or the total error based on biological variability. Adult recalibrated Jaffe results are in compliance with the goals based on biological variability and with the acceptance criteria from the NKDEP.
Improvement of dimensional stability of wood via combination treatment: swelling with maleic anhydride and grafting with glycidyl methacrylate and methyl methacrylate
Authors: Li Yongfeng , Wu Qinglin , Li Jian , Liu Yixing , Wang Xiang-Ming , Liu Zhenbo
Published: July 2011

A novel two-step combined treatment of poplar wood was developed to improve its dimensional stability. Maleic anhydride (MAN) was first employed to swell and bond to the wood cell wall, and then mixed monomers of glycidyl methacrylate/methyl methacrylate (GMA/MMA) were grafted to the cell wall through the chemical reaction with MAN within the wood cell lumen. The results of scanning electron microscopy and energy dispersive X-ray apparatus (SEM-EDX) and Fourier transform infrared spectroscopy (FTIR) analyses indicate that MAN penetrated and chemically bonded to the cell wall causing 9% volume swelling, and the copolymer from GMA/MMA monomers was grafted onto the wood cell wall, resulting in the improved interfacial compatibility between the polymer and wood matrix. The dimensional stability of poplar wood modified by the combined two-step treatment was remarkably improved compared with that of untreated poplar wood. The combination treatment of wood employed in this study proved to be more effective for improving the dimensional stability than treatment with PEG-1000 aqueous solution with 30% concentration.
Isolated GH deficiency: mutation screening and copy number analysis of HMGA2 and CDK6 genes
Authors: Gorbenko Del Blanco Darya , de Graaff Laura C G , Posthouwer Dirk , Visser Theo J , Hokken-Koelega Anita C S
Published: July 2011

Objective

In most patients, the genetic cause of isolated GH deficiency (IGHD) is unknown. By identifying several genes associated with height variability within the normal population, three separate genome-wide association studies provided new candidate genes for human growth disorders. We selected two of them for genetic screening of our IGHD population.

Aim

We aimed to determine whether high-mobility group A2 (HMGA2) and cyclin-dependent protein kinase 6 (CDK6) are involved in the pathogenicity of IGHD.

Methods

We directly sequenced coding regions and exon–intron boundaries of the genesHMGA2andCDK6in 105 Caucasian IGHD patients from the Dutch HYPOPIT study. In addition, we developed a new probe set of multiplex ligation-dependent probe amplification for both genes in order to detect copy number variations.

Results

In one patient with classical IGHD phenotype, we identified a new heterozygous 20 bp deletion in the intronic region ofHMGA2(c.250-29_-9del), which was absent in the databases and healthy controls. Together, with recently published data concerning the 12q14 microdeletion syndrome, where patients with anHMGA2haploinsufficiency had proportionate short stature, this study provides further support of the important role for HMGA2 in growth. InCDK6, we found only known polymorphisms.

Conclusions

This study provides the first report of a deletion in theHMGA2gene that might be related to IGHD. We suggest that this gene is investigated as a second screening in patients with a classical IGHD phenotype in which mutations in classical candidate genes have been excluded.
The growing role of gene methylation on endocrine function
Authors: García-Carpizo Verónica , Ruiz-Llorente Lidia , Fraga Mario , Aranda Ana
Published: July 2011

DNA methylation is the best studied epigenetic factor, playing a key role in producing stable changes in gene expression, thus defining cell identity and function and adapting cells to environmental changes. DNA methylation has also been recently shown to mediate cell responses to physiological endocrine signals. Moreover, alterations of the normal DNA methylation pattern can also contribute to the development of endocrine and metabolic diseases and can explain the relationship between an individual's genetic background, the environment, and disease. It should be remarked that although DNA methylation and demethylation are active processes, epigenetic changes produced during development can impact adult processes, establishing the idea that endocrine function can be persistently affected by events occurring in early life. Given the complexity of the endocrine system, both genetic and epigenetic processes, including DNA methylation, must be involved in its proper development and functioning. In this study, we summarize the recent knowledge in the field of DNA methylation and endocrinology. Given that DNA methylation can be involved in a number of endocrine and metabolic disorders, understanding and manipulating this modification opens a new door for preventing and treating endocrine diseases.
Differential regulation of Igf1 and Igf2 mRNA levels in tilapia hepatocytes: effects of insulin and cortisol on GH sensitivity
Authors: Pierce Andrew L , Breves Jason P , Moriyama Shunsuke , Hirano Tetsuya , Grau E Gordon
Published: July 2011

Igf1 and Igf2 stimulate growth and development of vertebrates. In mammals, liver-derived endocrine Igf1 mediates the growth promoting effects of GH during postnatal life, whereas Igf2 stimulates placental and fetal growth and is not regulated by GH. Insulin enhances Igf1 production by the mammalian liver directly, and by increasing hepatocyte sensitivity to GH. We examined the regulation ofigf1andigf2mRNA levels by GH, insulin, and cortisol, and the effects of insulin and cortisol on GH sensitivity in primary cultured hepatocytes of tilapia, a cichlid teleost. GH increased mRNA levels of bothigf1andigf2in a concentration-related and biphasic manner over the physiological range, with a greater effect onigf2mRNA level. Insulin increased basaligf2mRNA level, and strongly increased GH-stimulatedigf2mRNA level, but slightly reduced basaligf1mRNA level and did not affect GH-stimulatedigf1mRNA level. Cortisol inhibited GH stimulation ofigf1, but increased GH stimulation ofigf2mRNA level. The synergistic effect of insulin and GH onigf2mRNA level was confirmedin vivo. These results indicate that insulin and cortisol differentially modulate the response ofigf1andigf2mRNA to GH in tilapia hepatocytes, and suggest that the regulation of liver Igf2 production differs between fish and mammals. Regulation of liver Igf2 production in fish appears to be similar to regulation of liver Igf1 production in mammals.
Impact of 4-methylbenzylidene camphor, daidzein, and estrogen on intact and osteotomized bone in osteopenic rats
Authors: Komrakova Marina , Sehmisch Stephan , Tezval Mohammad , Schmelz Ulrich , Frauendorf Holm , Grueger Thomas , Wessling Thomas , Klein Carolin , Birth Miriam , Stuermer Klaus M , Stuermer Ewa K
Published: July 2011

The study investigated the influence of 4-methylbenzylidene camphor (4-MBC), daidzein, and estradiol-17β-benzoate (E2) on either intact or osteotomized cancellous bone in ovariectomized (Ovx) rats. Three-month old Ovx rats were fed with soy-free (SF) diet over 8 weeks; thereafter, bilateral transverse metaphyseal osteotomy of tibia was performed and rats were divided into groups: rats fed with SF diet and SF diet supplemented with 4-MBC (200 mg), daidzein (50 mg), or E2(0.4 mg) per kilogram body weight. After 5 or 10 weeks, computed tomographical, biomechanical, histological, and ashing analyses were performed in lumbar spine and tibia of 12 rats from each group. 4-MBC and E2improved bone parameters in lumbar spine and tibia, were not favorable for osteotomy healing, and decreased serum osteocalcin level. However, daidzein improved bone parameters to a lesser extent and facilitated osteotomy healing. For lumbar spine, the bone mineral density was 338±9, 346±5, 361±6, and 360±5 mg/cm3in SF, daidzein, 4-MBC, and E2, respectively, after 10 weeks. For tibia, the yield load was 98±5, 114±3, 90±2, and 52±4 N in SF, daidzein, 4-MBC, and E2, respectively, after 10 weeks. Serum daidzein was 54±6 ng/ml in daidzein group and equol was not detected.AlpandIgf1genes were down-regulated in callus after daidzein and E2compared with 4-MBC (week 5). The response of bone tissue and serum markers of bone metabolism could be ordered: daidzein<4-MBC<E2. Treatments were more effective after 5 vs 10 weeks. In SF group, bone structure was impaired after 5 weeks and improved after 10 weeks probably due to adaptation mechanisms to osteoporosis. In conclusion, it is conceivable that 4-MBC may improve bone tissue in osteoporotic organisms; osteoporotic patients with fractures could benefit from daidzein treatment.
Effects of soil density and earthquake intensity on flow deformation of the upper San Fernando dam
Authors: MING H.Y. , LI X.S. , ZHENG T.Y.
Published: July 2011

The seismic performance of the upper San Fernando dam is systematically studied by using a fully coupled finite-element procedure in conjunction with a unified state-dependent dilatancy sand model. With detailed information produced by this procedure, the effects of soil density and earthquake intensity on flow deformation of the embankment are examined. This paper provides convincing numerical evidence to prove that even though stronger earthquakes always produce larger deformation in the Upper San Fernando dam, an earthquake serves mainly as a trigger to initiate flow liquefaction. Once flow liquefaction is triggered by a sufficiently strong earthquake, the earthquake-induced flow deformation is controlled dominantly by the difference between the shear stress required for equilibrium and the shear strength of the liquefied soil, which is determined by its density under undrained earthquake loading conditions. The influence of the intensity of the earthquake itself on flow deformation of the embankment becomes secondary.
A Robust Approach to Field Development Plan Integrating Multi Dynamic Reservoir Models with Surface Network
Authors: Ojeke Akpoebi , Itotoi Ibiada Harrison , Nnamdi Dike , Umurhohwo Jonathan , Benjamin Osaigbovo
Published: July 2011

Recent advances in computing speed and software call for a better practical approach to subsurface-surface network modelling. Looking at it from the angle of Integrated Asset management, which requires the subsurface and surface teams to work as one in providing input and solution to field development plan challenges, this comes as an important tool in long term planning of a project. With this approach, team members from various disciplines, will be able to work directly with others, sharing ideas and making real time decisions on a regular basis.

The case study in this paper shows how such integration resulted in time and cost savings when good and quick decisions are made on a project. this shows a clear departure from the traditional subsurface/surface engineering relation in field development studies, where the subsurface reservoir simulation work is done independent of surface considerations. This paper highlights the benefits of the new approach to the project.
A Stochastic Approach to Well Spacing Optimization of Oil Reservoirs
Authors: John U. M-P. , Ibukun S. , Pius J. , Kayode O.
Published: July 2011

The subject of well spacing is one of importance in the petroleum industry. The well itself plays a very significant role in the development of the oil and gas reservoirs and in the control of the recovery process. However, determination of appropriate well spacing for maximum economic oil recovery and investment optimization has been a complicated and controversial issue in oil field development.

Previous papers on this subject have concentrated on deterministic evaluation of optimum well spacing to maximize returns on investment. A stochastic approach to fully account for uncertainties in input variables is proposed in this paper.

An analytical approach is used in developing the optimization model from an economic view point. The model is tested with one of the reservoirs of a Niger Delta field. Non-linear programming application is used to estimate the optimum well spacing from a population of input variables of different probability distribution. Uncertainty analysis is carried out using CrystallBall.

The result from the study carried out on the shallow and deep levels of a swamp field located in the Niger Delta, Nigeria gave the optimum well spacing for maximum returns on investment. Unlike the deterministic approach, the stochastic approach provided reasonable bounds for NPV that reflects the uncertainties associated with the input variables.

The optimum well spacing falls within reasonable bounds for field optimization and maximization of returns on investment. The combination of non-linear programming tool and stochastic approach provides a cost effective method in getting a quicker solution to the problem of well spacing.
Advances in Mud Design and Challenges in HPHT Wells
Authors: Godwin Woha , Ogbonna Joel , Boniface Oriji
Published: July 2011

The world's energy demand is rising and favourable economics has allowed oil companies prospect and drill for oil in deeper, more challenging frontiers (which are prone to high pressures and high temperatures) than ever before. There are vast reserves of hydrocarbons in these remote locations that promise to bridge the gap between demand and supply for energy. However HPHT prospects can be a formidable challenge. The mud weight (which is higher for HPHT wells) must be accurately controlled because of the very narrow mud weight windows. This high mud weight requirement leads to problems of high solid loading and barite sag. Technology to effectively monitor downhole pressure and temperature conditions is not well developed. Rig crews need to be adequately trained to adopt best practices in HPHT drilling to minimize the risk of well control issues. In this study, the conventional practices and procedures in mud design were studied and analyzed. Advances in mud design were highlighted and case studies of some HPHT wells in regions around the world were reviewed to learn the lessons and best practices that led to their success. Many of the conventional practices were found to be inadequate for HPHT drilling. Rigorous laboratory testing is necessary to generate detailed engineering guidelines for HPHT drilling fluids. Furthermore, a standard temperature concept used for controlling the surface mud weight was defined. The results of the new approaches to mud design and practices have been phenomenal. The importance of a stable mud system, detailed drilling program, best practices and correct field execution are fundamental. With the new approaches, many HPHT wells have been successfully completed in a cost effective manner and with no well control incidents recorded.
An Approach for Ranking Realizations to Characterize Reservoirs for Fluid Flow Simulation
Authors: Odai Lowestein , Ogbe David O.
Published: July 2011

Techniques in Geostatistics are increasingly being used to generate reservoir models and quantify uncertainty in reservoir properties. This is achieved through the building of multiple realizations to capture significant physical features in the reservoir. However, only a limited number of these realizations are required for complex fluid flow simulation to predict reservoir future performance. Therefore, there is the need to adequately rank and select a few of the realizations for detailed flow simulation.

This paper presents a methodology for building and ranking equiprobable realizations of the reservoir by both static and dynamic measures. Sequential Gaussian Simulation was used to build 30 realizations of the reservoir. The volume of oil originally in place, which is a static measure, was applied in ranking the realizations. Also, this study utilizes Cumulative Recovery and Average Breakthrough times from streamline simulation together with Geometric Average Permeability as the dynamic measures to rank the realizations. A couple of realizations selected from both static and dynamic measures were used to conduct a successful history match of field water cut in a case study.
An Improved Estimation of the Storage Capacity of Potential Geologic Carbon-Sequestration Sites
Authors: Lawal Kazeem A.
Published: July 2011

The ideas of open and closed-boundary systems are explored to investigate the technical limits of storage capacity of subsurface porous media, as required for the CO2-mitigation technology of carbon capture and storage (CCS). In particular; the effects of reservoir characteristics as well as the nature and mix of fluids that originally saturate the porous media are elucidated. An improved analytic method, premised on the concept of in-situ fluid displacement and replacement, of estimating the storage capacity of open systems is proposed and evaluated.

For closed systems, our analyses show that the general order of attractiveness (technical storage capacity) of potential sites is aquifer < water-depleted oil < undepleted oil < gas-depleted oil < depleted gas < undepleted gas formations. However, owing to the complexity of microscopic and macroscopic events, similar simple conclusion can not be drawn on the relative attractiveness of various open-boundary sinks.

As a case study, we examine the applicability of CCS in Nigeria. From first-order estimates of the pore volumes and other reservoir-fluid properties in Nigeria, we quantify the limits and time-scale of "available" geologic sinks to accommodate current and future loads of anthropogenic CO2 emissions from the Nigerian fossil-fired power sources.

Due to the relatively poor storage capacity of the potential sites compared to the anticipated CO2 load from power plants, which is just one of the CO2 sources, sequestration into underground formations may not, on its own, be a sustainable technical solution for Nigeria. Additionally, for the open systems, which define the upper limits of storage capacity, the potential challenges of managing displaced formation brine (and other less valuable fluids) may be overwhelming. As a complement, we offer some potential outlets for CO2 generated from these captive and other sources. Finally, long-term carbon-mitigation strategies hinged on mixed solutions are enumerated.
An Integrated Approach to Identifying and Reducing Reservoir Uncertainties in a Turbidite Deep Water Environment
Authors: Akingbade D. , Umurhohwo J. , Effiom O. , Pirmez C. , Weaver S.
Published: July 2011

Deep water developments have become increasingly challenging due to the heterogeneity of the reservoirs where complex architectures associated with turbidite deposition often results in reservoir compartmentalization and complex drainage pathways. These in most instances, result in sub-optimal reservoir development and sweep efficiency. Over the years, identifying and reducing the uncertainties associated with field development as a result of these compartmentalization and other complexities have been a major challenge to geologists and engineers in subsurface studies. This has necessitated the integrated application of high resolution 3D and 4D seismic, well logs, cores, latest techniques and concepts to narrow down the range of uncertainties for optimum reservoir management.

To reduce the uncertainty in the depositional architecture of the Bonga field reservoirs, a holistic approach involving the loop scale seismic stratigraphy interpretation techniques, detailed static and dynamic modeling strategy was adopted to determine the reservoir properties. The understanding of sub-regional to reservoir scale seismic stratigraphy has been used in framing the geological constraints which forms the basis for building realistic static and dynamic models. Loop-scale seismic stratigraphy is used to extract the maximum information from the seismic data. The static reservoir models are generated by a hierarchical workflow where large scale structures such as the channel complexes are modeled first, then the internal geometries such as the channel storey sets and finally the reservoir properties are populated based on well logs, cores and reservoir analogues. These static reservoir models are taken into the dynamic simulator where the reservoir uncertainties are re-assessed based on matching the production history and 4D seismic. The dynamic reservoir modeling involves the use of Stochastic Uncertainty Management techniques incorporating the Design of Experiment with the objective of narrowing the range of uncertainties in the subsurface parameters.

Integrating the static and dynamic modeling of the reservoirs provides a major improvement in our understanding of the subsurface by eliminating scenarios that do not honor all of the data available. This study has resulted in subsurface models that represent an improved understanding of reservoir property distribution and connectivity. These models are being used for improved reservoir management strategies and effective field development planning.
Analytical Evaluation of Kukaku Field
Authors: Qiang Ma , Samson Ibukun , Kenneth Eke , Odogu David , Onyekonwu Mike
Published: July 2011

Analytical studies serve as the primary (first pass) models for evaluating field performance before proceeding to full field numerical models. The decision to proceed to a full field numerical model is usually determined by results of the analytical study and cost of the study relative to the estimated reserves in the field. This implies that for smaller fields, analytical studies may be the major reference for field development.

This paper presents the workflow and results of integrated analytical studies performed on Kukaku, an onshore field in Niger Delta belonging to the Nigerian Petroleum Development Company (NPDC), jointly operated by NPDC and SIPEC. The studies done include petrophysical analysis, welltest (DST) interpretation, NODAL™ analysis, choke performance studies, coning studies and material balance forecast. The paper focuses on key areas of integration in the workflow and best practices in the study.

Conclusion from the study is that integration is also a key concept in analytical field studies especially for smaller fields in which the reserves size precludes the use of expensive numerical models. In such cases, critical analysis of available data and best use of such data to generate rigorous and robust analytical models are key to the optimal development of such fields.
Application of 4D Seismic Response as a Screening Tool in Assisted History Matching
Authors: Bakare Olatunji , Umurhohwo Jonathan , John Ikomi , Okonkwo Arinze , Tope Fehintola , Benjamin Osaigbovo
Published: July 2011

It is best practice in reservoir engineering to have a probabilistic distribution of expectation ultimate recovery all within the scope of credible history match. A P90, P50 and P10 function can thus be derived from such distribution. In most cases the basecase deterministic model is almost always not too far from the probabilistic P50 case. To properly quantify the whole range of key uncertainties engineers are increasingly turning to Design of Experiment (DoE) and Assisted History-Matching (AHM). Understanding the fundamentals is key, implementing the DoE is even more imperative and relating it to the ‘behavioural’ antecedent seen in the reservoir will go a long way to obtaining credible history matches. This paper details how the workflow of DoE/AHM was used to quantify the impact of key uncertainties in obtaining a wide range of credible history match for reservoirs in the Bonga field. 4D seismic response was used to further screen the equally probable models arriving at fit for purpose models constrained to observed fluid movement. This approach focused on the use of saturation changes with direction and sizes of the flood fronts to select models that show little deviation from the 4D seismic response, and reject those that show a large deviation.
Application of Intervention Analysis to Oil and Gas Production Series in Niger Delta, Nigeria
Authors: Biu Oyinebifun. E. , Iwueze Iheanyi. S.
Published: July 2011

There seems to be a rush towards the ever increasing literature on the Niger Delta Area of Nigeria, where crisis has been the order of the day. Interestingly the existence of enormous oil and gas reserves in the region and the threat of disruption of its extraction by the militants have increased globally which has led to drastic reduction in Oil and Gas production in the region. It is of interest to study whether or not the reduction materialized and the measure of this reduction in order to maintain stability in the region. The effect of an intervention on Oil and Gas production series was studied using (i) the usual intervention analysis of Box and Tiao (1975) where AR(3) model with constant was built for the pre-intervention sample and an intervention model was identified for the intervention period for the data set. (ii) CUSUM charts were constructed to monitor changes in the process level after the intervention. The result from the CUSUM chart shows that the crisis in the region have reduced oil production for about 12 or 13 months and Gas production for 8 or 9 months. Thus, it seems reasonable to conclude that the militant attacks in Niger Delta region were instrumental in the reduction of Oil and Gas production.
Application of Microlog in Net to Gross Uncertainty Management
Authors: Agubaeze John , Arochukwu Elias , Kehinde Dare , Simon Roya
Published: July 2011

Net to Gross (N/G) is a key input parameter into the estimation of Hydrocarbon In-Place volume. Errors in N/G evaluation could result in huge impact (up to 40%) on estimated in-place volumes which would in-turn affect the economics of reservoir/field development.

Traditionally Gamma ray (GR) and/or SP logs are used for delineating reservoir sands from non-reservoirs. However, in some instances, these logs are not able to differentiate fully some reservoirs from non-reservoirs. In the case of GR, it is not able to resolve differences between shales and sands with high radioactive materials contents. Both GR and SP logs do not differentiate non reservoir cemented tight sand formations. This lack of contrast on the logs in such circumstances results in errors in the estimated net reservoir sands, leading to inaccuracies in the overall estimated reserves.

To account for the deficiencies of these traditional techniques, a combination of neutron porosity and formation density logs may be deployed. These tools are able to provide contrasting petrophysical properties that differentiate between impervious formations and reservoir sands, thereby providing robust technique for improved net sand estimation.

Incidentally, most old wells drilled in the 1950s up to mid 1980s do not have the neutron and the density logs. Yet for some early operators, a majority of the old wells were strategically positioned that the openhole data from them would be very crucial for estimation of reserves in the concerned fields. A cursory review of the log database reveals the abundance of Micrologs (Microlog Normal (MLN) and Micro Log Inverse (MLI)) in most of the early wells. Careful re-interpretation of these logs using appropriate techniques and principles have resulted in significant improvement in net-to-gross estimation in the absence of neutron and density logs.

This paper aims at re-establishing the resourcefulness of microlog data in error reduction on estimated net to gross with a case study in ELJODA Field, Niger Delta Nigeria.
Application of the Excess Pressure Technique to Investigate Connectivity of Deepwater Turbidite Reservoirs, Offshore Nigeria
Authors: Jenakumo T. D , Ranasinghe M. K
Published: July 2011

The importance of communication between well pairs in deep water turbidite reservoirs, where water injection is the main reservoir drive mechanism cannot be overemphasized. Well costs continue to be on the rise and well redundancy due to lack of communication between injector-producer pair is undesirable. Compartmentalization within reservoirs - vertical, lateral or both is a common phenomenon, and its detection is increasingly becoming significant in reservoir characterization. Whereas the use of linear pressure trends to infer vertical connectivity or otherwise is very well established, well-to-well data evaluation is critical for assessing lateral connectivity.

In this work, residual pressure (commonly known as excess pressure) plots have been employed to evaluate connectivity between vertically stacked reservoirs which are otherwise assumed to connected under static conditions. We have tried to incorporate all available data types, including well logs, PVT sample analysis and geochemical interpretations prior to drawing conclusions on the risk of compartmentalization for each case. We have evaluated formation pressures and gradients from wells and compared the results against the accuracy of the wireline formation tester (WFT) tool.

The first set of reservoirs evaluated is from an Appraisal field where development wells are being planned. The results will be compared to the pre-production wells from the an Analogue fieldwhich has been producing for over five years now. This work will then try to establish whether the excess pressure plots from the Analogue field could have predicted some of the production observations that are seen today. And if so, comment on what an excess pressure threshold may be for this region. Both the Appraisal and Analogue fields lie the same block.

For the Appraisal field, this study is useful as a means of assessing the risk of intra-reservoir compartmentalization and provide an opportunity to optimize future development plans.
Avoiding Misleading Performance Predictions for a Reservoir System with Limited Production Data by the Application of Experimental Design Technology
Authors: Cyril Ogbalor , Peacock Anthony
Published: July 2011

The general aim of reservoir modelling is to provide a tool capable of generating reliable ranges of performance predictions on which to make development and investment decisions in a way that manages the recognised uncertainties associated with the development. The standard approach is to generate a range of static and dynamic models and parameters that capture the uncertainties, based on available sub-surface and surface information, correlations or engineering judgement.

Experimental design (ED) techniques are being increasing adopted as a method to consistently combine the uncertainty parameters and to construct a range of reservoir models. The standard ED approach is to adopt global changes to the range of input parameters and seek combinations that best reproduce the historical data. Calibrating the reservoir models to available historical performance data is a vital step in providing confidence on the predicted results. However, in situations with limited performance data, great care is needed to understand the implications of model calibration so as to avoid misleading prediction results.
Capillary Pressure Curves from Nuclear Magnetic Resonance Log Data in a Deepwater Turbidite Nigeria Field - A Comparison to Saturation Models from SCAL Drainage Capillary Pressure Curves
Authors: Arogun Olubunmi , Nwosu Chike
Published: July 2011

The DW Turbidite field in Deepwater Nigeria has limited SCAL data on drainage capillary pressure curves used, traditionally, in building saturation-height functions for application in 3D static and dynamic models.

An alternative approach to derive capillary pressure curves from Nuclear Magnetic Resonance (NMR) T2 distributions, developed by Volokitin et al, has been tested in one of the key reservoirs in the DW Turbidite North field and compared to mercury injected capillary pressure (MICP) data from a full-bore core across the reservoir.

The alternative approach relies on an underlying assumption that a relationship exists between porebody radius (as represented by the NMR T2 distribution) and pore-throat radius (which drives capillary behavior). An algorithm has been applied that uses a T2 cutoff such that the sum of the bound and moveable fluid spectra amplitudes matches the water porosity to correct for the presence of hydrocarbons. The hypothesis is the resulting relationship (between the NMR T2 distribution and pore-throat distribution) embedded within a proportionality parameter, κ.

The hypothesis was tested on the three key facies (CSA - Channel Storey Axis, CSM - Channel Storey Margin & ICTB - Inter-Channel Thin Beds) identified in the reservoir. Field-specific proportionality parameters were determined from which NMR T2 capillary pressure curves have been derived.

Comparison between the derived capillary pressure curves and the SCAL (MICP) data provide confidence that this technique can be applied in the absence of SCAL data.
Challenges and Remedy for Cementing of HPHT Wells in Nigerian Operation
Authors: Yetunde Shado , Ogbonna Joel
Published: July 2011

As hydrocarbons are being depleted from some formations, the search is on for greater reserves in difficult regions. Some wells are now drilled in more hostile downhole conditions, which include high temperature and high pressure. A well is considered to be high pressure and high temperature (HPHT) if the pressure exceeds 15000psi (1020 bar) and the temperature exceeds 300°F (149°C). The challenges created by these, make drilling and cementing in these regions difficult. The study reveals that in order to meet up with the challenges of HPHT drilling and cementing operations, issues such as effect of temperature and pressure, large stresses, degradation of set cement at elevated temperature, small ECD windows, efficient fluid design and displacement among others must be addressed for successful job execution and excellent job delivery.

The objective of the study therefore is to highlight various challenges associated with HPHT wells, the Best Practices that have been adopted in several HPHT wells and the way forward. This will provide a learning point for operators, researchers and other Engineering professionals especially for the emerging HPHT operations in Nigeria and Gulf of Guinea.