bluuebunny/crossref_metadata_2025 huggingface dataset:
New Grids for Robust Reservoir Modeling
Authors: Gringarten E. , Arpat B. , Haouesse A. , Dutranois A. , Deny L. , Jayr S. , Tertois A. L. , Mallet J. L. , Bernal A. , Nghiem L.
Published: September 2008

Geostatistical modeling of reservoir facies and petrophysical properties (e.g. porosity and permeability) must be performed in a pre-faulted, deposition space in order to reproduce the true spatial correlations of these properties. A transformation function is therefore required to bring the data from the current position of the reservoir into the modeling space where experimental variograms are computed; reservoir properties are then stochastically simulated in the deposition space and mapped back to the real space. Current reservoir modeling practice uses a stratigraphic grid to conform to the reservoirs structure (bounding horizons and faults). The (i, j, k)-indexing of the nodes of the cells is used as a discretization of a curvilinear coordinate system which acts as the transfer function to the deposition space. This leads to a very strong underlying assumption: the geological distances (in the deposition space) are a function of the (i, j, k)-indexing. In the presence of non-vertical faults, the cells of the stratigraphic grids are either stretched or squeezed, violating this assumption. Moreover, in the presence of complex structural geology, these grids simply cannot be constructed without tremendous simplifications. The new proposed approach uses a 3D parameterization of the subsurface yielding a grid that minimizes the distortions of distances imposed by geostatistical simulation algorithms. These new Geologic Grids allow the construction of robust reservoir models whatever the structural complexity of the reservoir. Additionally, they guarantee the accurate mapping and upscaling of reservoir properties into either structured or unstructured Flow Simulation Grids. They also enable the creation of structured Flow Simulation Grids in which faults are defined as stair-steps allowing representation of the complete reservoir structure and ensuring orthogonality of cells.
Accurate Single-Ended Distributed Temperature Sensing
Authors: Chen Yuehua , Ramos Rogerio T. , Hartog Arthur H. , Greenaway Robert , Powell Giles , Taylor David
Published: September 2008

Distributed temperature sensing (DTS) is a technique to obtain real-time temperature well logs which are used for several applications such as production allocation, heavy oil thermal recovery (e.g., steam-assisted gravity drainage, SAGD) steam-well management, and well-integrity monitoring. This system is based on measuring scattered light at more than one wavelength from an optical fiber placed along the well.

An issue arises when the attenuation of the optical fiber changes with time by different amounts at the different wavelengths used causing degradation in accuracy of the measurement. This differential loss can be compensated for by connecting both ends of the optical fiber to the DTS instrument in a double-ended (DE) configuration. However, it is not always possible to operate in DE configuration because of other constrains in the design such as lack of space or restricted number of penetrations in completion equipment. Single-ended (SE) operation configuration has been used in these cases, exposing the monitoring system to potential loss of accuracy.

An accurate single-ended (ASE) DTS system which provides differential loss measurement and compensation to single-ended installations is described. The instrument uses more than one light source to compensate for the optical-fiber differential losses at the relevant wavelengths. This compensation is applied continuously without the need of external recalibration. A system operating on this principle has been used for some time on single-mode fibers, and recent technical advances have enabled its application to multimode fibers.

Laboratory-test and field-test results are presented showing a dramatic improvement in accuracy in cases where differential losses have developed. Comparative data using DE, SE, and ASE DTS systems are presented showing cases in which optical fibers were subjected to extreme environments where the effect of differential loss is accentuated. Examples are shown in which errors of up to 100°C caused by differential loss were automatically corrected in real time by the ASE DTS instrument.
Capillarity Controlled Displacements in Sediments With Movable Grains: Implications for Growth of Methane Hydrates
Authors: Prodanovic Maša , Bryant Steven L.
Published: September 2008

Gas invasion of sediments is one mechanism by which methane hydrates are believed to form. As the capillary pressure exerted by an accumulated gas phase below the hydrate stability zone increases, it can exceed the entry pressure of the sediment within the hydrate stability zone, leading to a drainage displacement. Alternatively it can exceed the parting pressure of the sediment, leading to a gas-filled fracture propagating into the sediment. In unconsolidated ocean sediments, the capillary pressure may also be large enough to move grains apart during drainage. This motion alters the pore throat sizes which control subsequent drainage of the sediment. A model for the dynamics of this process is useful for assessing the competition between drainage (controlled by capillary forces) and fracturing (controlled by pore pressure and earth stresses). This in turn provides insight into the possible growth habits within the hydrate stability zone.

To model this process we consider immiscible displacements when fluid/fluid interfaces are controlled by capillary forces. The progressive quasistatic (PQS) algorithm based on the level set method readily determines the pore level geometry of these interfaces. Capillary pressure generally exerts a net force on grains supporting an interface. We extend PQS algorithm to implement a kinematic model of grain displacement in response to that force. We examine the changes in the drainage curve caused by this coupling. We compute the interfacial area associated with the bulk water phase, anticipating preferential growth of methane hydrate there.

When grains can move in response to net force exerted by the gas phase, small variations in an otherwise uniform distribution of pore throat sizes lead to self-reinforcing, focused channels of gas phase. In contrast to behavior in stationary grains, the drainage curve exhibits no clear percolation threshold. Displacements in materials with broad throat size distributions also exhibit self-reinforcing channels. Behind the leading edge of the displacement front, the net force exerted on the grains tends to push them together. This effectively seals off these regions from subsequent invasion. Thus hydrate growth tends to be localized along the channel of displaced grains.
Identifying Inefficient Drilling Conditions Using Drilling-Specific Energy
Authors: Armenta Miguel
Published: September 2008

A novel correlation identifying inefficient drilling conditions is presented using experimental and field data. Historically, Mechanical Specific Energy (MSE) has been used to improve the drilling performance with mixed results. Drilling Specific Energy (DSE) is the amount of energy required to destroy and remove underneath the bit a unit volume of rock. DSE includes axial, torsional and hydraulic energy. DSE is different than MSE because it includes a hydraulic term. The initial MSE correlation (Teale, 1964) has been modified to accommodate the new hydraulic term.

Experimental and field data presented on the paper show that DSE can be used to identify inefficient drilling conditions. Experimental results illuminate the importance of including bit hydraulics into the specific energy analysis for drilling optimization. Field results reveal specific patterns for inefficient drilling conditions such as; bit balling and friction limited wells. These field results also enligthen a good correlation between the calculated DSE and the rock compressive strength.

The novel correlation presented in this paper will help to improve the drilling efficiency worldwide. The new hydraulic term included on the specific energy correlation is the key to correctly matching the amount of energy used to drill and the rock compressive strength. Also, this new term illuminates how much hydraulic energy is needed to drill faster and efficiently when the mechanical energy (axial and torsional) is increased.
Sand or Mud Removal in Low Bottom Hole Pressure Wellbores Using Jet Pump and Concentric Coiled Tubing Leads to Improved Production
Authors: Li J. , Crabtree A. , Kutchel M. , Diaz J. , Reyes W. , Dugarte R. , Peña L.
Published: September 2008

Horizontal drilling and completion are common practice for accessing conventional and heavy oil reservoirs. During the drilling process, the formation pore pressure is less than the drilling fluid's hydrostatic pressure. This can lead to some fluid loss before a filter cake is formed to prevent further mud losses. For unconsolidated formations, it is prefer to keep the filter cake in the place to maintain the hole's integrity during the well completion period while running the liner. However, the filter cake can be broken down by the sliding and rotating of the bottom hole assembly. These breakdowns can lead to high completion fluid losses to the formation. Sand production is also a common problem associated with unconsolidated formations. These drilling & completion practices, sand production, have resulted in a demand for well intervention that can economically remove mud damage and produced fill throughout the whole length of horizontal wells.

Since 1995, a technology combining concentric coiled tubing (CCT) with a jet pump has been developed and used to remove both the drilling fluids, filter cake and solids. Initially it was developed for horizontal heavy oil reservoirs where pressures are low and oil viscosity is high, without placing hydrostatic loads on the reservoir. The job data from more than 600 sand/well vacuuming operations worldwide has been compiled into a database.

This paper reviews the well information and the key operating parameters: maximum depth, bottom hole pressure gradient and pump rate. The engineering challenges, best practices and lessons learned from the sand/well vacuuming process are also summarized. Analysis of this data yields a better understanding about the vacuuming technology and provides good guideline for future operations.

Case histories are provided demonstrating how to deploy the different sand/well vacuuming bottom hole assemblies (BHA) for different applications. Post job analysis indicates CCT vacuuming technology reduces the skin damage and increases the production compared to non-vacuumed wells. Moreover, the details estimated from sand and other fluid influx profiles along the wellbore during the vacuuming process, are used to evaluate well production and develop a management strategy.
From Mega-Cell to Giga-Cell Reservoir Simulation
Authors: Dogru Ali H. , Fung Larry S. K. , Al-Shaalan Tareq M. , Middya Usuf , Pita Jorge A.
Published: September 2008

For many oil & gas reservoirs, especially large reservoirs in the Middle East, the availability of vast amounts of seismic, geologic and dynamic reservoir data result in high resolution geological models. Because of the limitations of conventional reservoir simulator technologies, high resolution models are upscaled to flow simulation models by reducing the total number of cells from millions to a few hundred thousand. Flow simulators using upscaled reservoir properties produce average reservoir performance and often fall short of accurately predicting recovery.

Realizing the limitations of the conventional simulators for the giant oil and gas reservoirs, parallel reservoir simulators have been developed. The first generation of parallel simulators increased the simulator capabilities by an order of magnitude — the result was that mega (million) cell simulation became a reality. Parallel computers, including PC Clusters, were successfully used to simulate large reservoirs with long production histories, using millions of cells. Mega-cell simulation helped recover additional oil and gas due to better understanding of reservoir heterogeneity. The speed of parallel hardware also helped, making many runs to address uncertainty possible.

Despite the many benefits of parallel simulation technology for large reservoirs, the average cell size still remains in the order of hundreds of meters (m) for large reservoirs. To fully utilize the seismic data, smaller grid blocks of fifty m in length are required. This size of grid block results in billion (Giga) cell models for giant reservoirs. This is a two orders of magnitude increase from the mega-cell simulation. To simulate Giga-cell models in practical time, new innovations in the main components of the simulator, such as linear equation solvers, are essential. Also, the next generation pre- and post-processing tools are needed to build and analyze Giga-cell models in practical times.

This paper describes the evolution of reservoir simulator technology, from Mega-Cell scale to a Giga-Cell scale, presenting current achievements, challenges and the road map for Giga-Cell Simulators.
Application of the Efficient Frontier Concept to Resource Play Budget Evaluation and Portfolio Optimization
Authors: Tonnsen Robert R.
Published: September 2008

The oil and gas industry contains significant inherent risks that greatly affect a company's ability to achieve predicted performance. In an attempt to better manage risk and uncertainty during the decision making process, the efficient frontier concept has been proposed as a method for portfolio optimization. This paper analyzes the application of the efficient frontier concept to a yearly budget allocation process considering unconventional resource play opportunities. Economic and optimization models were developed with assumptions specific to resource plays. The models show that the expected risk, uncertainty, and return on investment change according to the level of investment, project selection, the number of planned wells, and to the grouping of wells for budgeting purposes. The budget dependency of the risk and return cause an oddly shaped efficient frontier resulting in mean-variance efficient portfolios that may not be optimal when based on a set level of risk. In addition, the results show that conventional rank and cut methods for portfolio selection may suffice for resource play budget allocation. However, even though the efficient frontier does not often offer definitive solutions for portfolio optimization, illustrating the interactions among portfolio properties and providing insight into inefficient budget allocations could make the efficient frontier optimization process invaluable.
Sand Quantification: The Impact on Sandface Completion Selection and Design, Facilities Design and Risk Evaluation
Authors: Addis M. A. , Gunningham M. C. , Brassart Ph. , Webers J. , Subhi H. , Hother J. A.
Published: September 2008

Sand Quantification involves predicting the volumes of sand which can be produced at the sandface completion and transported to the surface facilities for different operational scenarios. Sand quantification estimation is still novel in the industry, and this paper describes its application in completion selection and design, facilities design and operation, and facilities risk evaluation, with reference to a high rate gas field development.

The estimation of sand production volumes for openhole and cased and perforated completions is presented for the high rate gas wells, along with the workflow used for the selection and optimisation of the completion design, based on these estimates. The optimum completion aims to delay the onset of sand to surface for the first 18 years of production, whilst maintaining high gas productivity (>300mmscf/d/well). The selection of contingency sandface completions is also discussed along with mitigation measures in the event of unexpected sand production. The impact of the sand quantification on surface facilities design is discussed based on a probabilistic approach, along with the operational procedures identified to manage this sand.

The operational evaluation is based on a Quantitative Risk Analysis (QRA) of the facilities and wells, which helped identify operational changes to further reduce the ‘as built’ low risk operation. This use of sand quantification for completion design and for QRA of facilities forms a new capability and an extension to the existing use of sand prediction technologies.
Development of a Response Surface Based Model for Minimum Miscibility Pressure (MMP) Correlation of CO2 Flooding
Authors: Ghomian Yousef , Pope Gary A. , Sepehrnoori Kamy
Published: September 2008

Correlations are commonly used to predict CO2 multiple contact miscibility (MMP) since such correlations are generally inexpensive and easy to use. In this study, we used a novel approach based upon four dimensionless scaling groups commonly used for hydrocarbon phase behavior modeling (reduced temperature and acentric factors for light and heavy pseudo components) as well as multivariate regression analysis based on response surface methodology to develop an MMP correlation for a broad range of reservoir oils. Applying the response surface method and multivariate regression analysis made it possible to quantify and rank the effect of each one of the mentioned dimensionless groups on the predicted MMP value. Since reservoir temperature is one of the main parameters, slim tube simulations were performed at four different reservoir temperatures (90, 150, 180, and 220 °F) for all of the fluid models. Based on the results from these simulations, and by performing multi-variate regression analysis, MMP values were correlated using a response surface based on linear, quadratic, and third degree equations. Our new MMP correlation takes into account the important equation-of-state properties for heavy- and light-oil components as well as temperature. Predicted MMP values from the new correlation were compared with previously published MMP correlations and found to have a lower average error.
Pressure Transient Analysis in Partially Penetrating Infinite Conductivity Hydraulic Fractures in Naturally Fractured Reservoirs
Authors: Igbokoyi Alpheus O. , Tiab D.
Published: September 2008

Although the effect of partial penetration of an infinite conductivity hydraulic fracture has been considered in a homogeneous reservoir, there is no study in similar problem in naturally fractured reservoirs. This paper presents the analysis of the solution to such problem in naturally fractured reservoirs. The method of analysis with or without type curve that enables us to evaluate the permeability in the three principal axes directions is also presented.

The solution to the mathematical model was obtained in Laplace domain with elliptical flow model. Several type curves were generated to study the pressure behavior. Both the early linear and pseudo-radial flow regimes are observed. The duration of the early linear flow regime is a function of the natural fractures storativity ratio, interporosity flow coefficient and the dimensionless hydraulic fracture's height. The effect of the dimensionless hydraulic fracture's height on the duration of the linear flow becomes negligible as its dimensionless height approaches unity. Therefore there is no single unique value of a dimensionless time for the end of the linear flow regime as in the case of homogeneous reservoir. Raghavan et al (1978) determined the end of the linear flow regime in fully penetrating hydraulic fractures in homogeneous reservoir to be 0.016. This value is based on the dimensionless pressure drop only. In this study, this value was found to be 0.01 and it was evaluated with pressure derivative curve which is more accurate.

Two simulated examples were used to validate the method of the analysis developed. The results obtained are in agreement with the input data.
Analyzing Buildup Data Following a Highly Unstable Rate History
Authors: Larsen Leif
Published: September 2008

This paper addresses practical aspects of analyzing buildup data following a highly unstable rate history, such as cases where the rate decreases or increases significantly prior to shut-in, or even drops to zero (well dies) "prior" to a normal shut-in. Although any rate history can be approximated with a piecewise constant rate history, it turns out that a piecewise linear rate history with a modified superposition expression more readily can be used to recognize standard flow regimes and to determine formation flow properties when the rate prior to shut-in varies sharply with time. The simplest cases considered are based on a single flow period with the rate changing linearly from a low to a high value or from a high to a low value prior to shut-in, including cases starting or ending at zero. For such cases it is easy to overlook a simple flow model if single-rate analyses are attempted with an average rate or some other expected representative rate value.

With piecewise linear rate histories it is possible to accurately represent piecewise monotonic rate changes with just a fraction of the number of rate changes needed with a piecewise constant history. Meunier et al.1 took advantage of this in a paper dealing with analyses of afterflow data. The present paper extends this approach to arbitrary cases with rapidly increasing or decreasing rates prior to shut-in or scattered throughout a test sequence. To do this in routine analyses the method must be included in standard software packages for well test analysis. For direct matches of data and models this requires integration to replace simple difference expressions, but this can be handled automatically by the software without user input. Without the software option the results can at least be implemented in spreadsheet applications for test designs and analyses if necessary basic solutions for radial flow with storage and skin, or more complicated models, are available. For specific flow regimes (radial flow, linear flow, etc.), this can be handled with closed-form expressions without numerical integration routines.

Only synthetic cases have been included to illustrate the characteristics of buildup data influenced by changing rate prior to shut-in. The synthetic cases are all of the simplest type, with just one flow period prior to shut-in. Theoretical results about more complex cases are presented, but to illustrate the characteristics of buildup data following unstable flow, it was concluded that the simplest cases were best suited to this end. Results are presented both for simple semilog data sets and for data generated from a model with wellbore storage and a single fault added to increase the complexity of data.
Real-Time Data Enables Real-Time Decision Making in Well Intervention Operations
Authors: Huval Sidney , McNicol Jim
Published: September 2008

Modern well intervention operations bring with them serious risk of non-productive time (NPT) and cost escalation through the customary practice of working "blind" – that is, by relying solely on surface measurements such as RPM, hook weight and rotary torque to manipulate well intervention tools tens of thousands of feet downhole. Often the true results of these manipulations are not known until the bottomhole assembly (BHA) has been retrieved to surface, and then further trips become necessary to complete a satisfactory intervention operation. Until now, there has been no accurate or consistent method for observing the forces and conditions experienced in the downhole intervention environment.

A new system has been developed to present quantified parametric downhole tool force and environment information to the operator at surface in real time and thus enable on-the-spot decision making for the optimization of well intervention operations. The system integrates a sensor sub and a basic measurement while drilling (MWD) tool into the intervention BHA. Standard mud pulse technology transmits signals to surface for decoding and visualization by an independent stand-alone unit.

A significant number of successful operations have been conducted during system integration testing, and the first commercial jobs have just been completed. This paper will demonstrate the benefits of real-time data enabling real-time decision-making in challenging well intervention scenarios, and through case history data, elucidate new refinements in the system architecture.
Efficient Region Decomposition for Parallel Simulation Accounting for Uncertainty in the Reservoir Model
Authors: Kim Yonghwee , Srinivasan Sanjay , Bryant Steven L.
Published: September 2008

Reservoir region delineation is essential for parallel flow simulation of large reservoir models. We argue that the delineation of least correlated, most sensitive regions mitigates the requirements for load-balancing and flux-matching that are the bane of current parallel simulation procedures. The optimal choice of sub-regions satisfies two conditions. First, the values of permeability in the sub-regions should have the greatest influence on the performance of injection and/or production wells. Second, the sub-regions should exhibit the least possible correlation with one another. Principal component analysis (PCA) of sensitivity matrices readily identifies regions meeting both the conditions. There are two methods for obtaining sensitivity matrices: i) the Hessian matrix calculated internally by a flow simulator, and ii) a covariance matrix calculated using a suite of realizations. The latter method is more robust and effective in terms of fluid flow connectivity, computational cost, availability to implement and capability of capturing uncertainty of reservoir models. In this paper, we focus on domain delineation using the covariance matrix and apply the method to a series of examples. We discuss key advantages of this method over the alternative of using the Hessian matrix.
A Decade of Experience—The Water-Based Thermal Insulating Packer Fluid
Authors: Javora Paul H. , Pearcy Rick , Wang Xiaolan , Stevens Dick , Qu Qi
Published: September 2008

The concept of ‘flow assurance’ has numerous connotations, especially when it comes to deepwater operations. Just a decade ago as deepwater came into vogue, flow assurance terminology would primarily refer to chemical injection technology. This quickly changed however, as demand for effective thermal insulation techniques to prevent annular pressure buildup, costly wax and asphaltene deposition, and gas hydrate formation escalated. Concurrently, effective water-based insulating fluids were introduced into the field, and were quickly accepted as a valuable method to retain heat in produced fluids and prevent heat loss to external annuli and surrounding environments. To date, over 70 installations of water-based insulating fluids have been completed, with applications ranging from controlling annular pressure buildup, to controlling heat loss in one or more riser annuli.

This paper presents case histories from the originally designed insulation requirements in casing to control annular pressure buildup, to new evolutions applicable in modern risers. Operational details of installations completed, successful removal of the insulating fluid from wells, and successful re-use of the removed insulating fluids are presented. Results from an unexpected long-term shut-in, and field data connecting the effectiveness of water-based insulating fluids to model predictions are also presented.
Prudhoe Bay Well P2-15 Surface Casing Failure
Authors: Anders J. , Cismoski D. , Daniel R. , Dube A. , Engel H. , Hughes A. , Norene T. , Hamilton R. , Mohr W.
Published: September 2008

While pre-heating the surface casing landing mandrel in preparation of welding to repair a leak on Prudhoe Bay well P2-15, the wellhead suddenly and unexpectedly moved downward approximately 18 inches. This failure resulted in an injury and required a rig workover to repair the well.

The wellhead was cut below the surface casing landing mandrel and sent to a company specializing in metallurgical analysis to determine the cause of movement. A section of the surface casing was identified with reduced wall thickness due to drilling wear. As heat was applied to raise the wellhead to welding temperature, the reduced wall thickness section of the surface casing experienced a temperature increase greater than the design pre-heat temperature. This thin-walled section of the casing began losing tensile strength, eventually resulting in the surface casing collapsing inward and allowing the wellhead to rapidly subside.

This paper discusses the causes of the failure and presents recommendations to prevent future failures of this type.
Thermodynamics of Compact Downhole Turbo Generators
Authors: Fernandez V. John , Ghosh Parthasarathi , James Darryl
Published: September 2008

A turbine assembly for downhole use is being developed for use in drill pipe and annular locations in the well that require small power generation devices. Such devices are required in high speed data transmission drilling strings currently being introduced in the industry. Discrete array of sensor banks mounted on the wired drill string require a local power source that directs electric energy to tools located in a particular sensored section of the well being drilled.

The thermodynamics of the compact generators is typically cyrocooling with reverse Brayton cycle expansion, liquefying in bulk gases such as helium. The high efficiency compared to membrane separation makes this method of helium distillation suitable for diverse uses such as NMR equipment and superconducting conductors.

This paper details the thermodynamics of a high-efficiency cycle power generation system for such drill strings the development of components in the system used to arrive at the target efficiency levels defined by the generation cycle. The lessons learnt from the cryogenic compact turboexpanders, which include mixed radial inlets and axial discharge configurations are illustrated in the development of this turbine generator for downhole drilling use. Additionally, supercomputer simulations on structural and fluid mechanics conditions downhole are used are used to understand, in detail, the system and component level thermodynamics of the turbo-generator.

The conclusions of this thermodynamic cycle development work is that a small profile, side-mounted power source can be development for use in drilling applications, particularly where the center bore of the drill string is required to be a clear pathway. The small profile of this solution enables completion strings used in intelligent fields to be powered, in addition, where the side-mounted power source is readily integrated into small cross-sections.
3D GIS as an Integrated Framework for Drilling Site Location Optimization
Authors: Ershaghi Milad A.
Published: September 2008

Given a table of 30,000 coordinate pairs representing the geographic locations of potential sites for new wells to be drilled and a repository of lease, platform, pipeline, directional survey, production, and chronostratigraphic data spanning the Gulf of Mexico region, we demonstrate how a 3D GIS can be used as an integrating technology to facilitate determination of the optimal well location.

Previous studies have highlighted the user interface, data management, 2D analytical, and surface visualization capabilities of GIS technology as it applies to E&P workflows, but have not addressed the same technology's programmatic customization, 3D analytical, and subsurface visualization capabilities. This is due in part to the fact that the range of features and capabilities found in tools that ship with the GIS product are adequate for most GIS users' needs, and the justification to explore the software's programmatic capabilities is frequently unmet. Furthermore, 3D technology is relatively new, tools supporting visualization and analysis based on 3D technology are in limited availability, and 3D has traditionally been regarded as a non-vital feature of information visualization rather than a dimension of data upon which analytical processes can be improved.

Through custom code written that programmatically exercises the GIS software's engine via an API, we demonstrate how vector geometry representations of features can be persisted into a geospatial database, 3D computational geometry interfaces can be used to derive new vector datasets from this data, geostatistical interpolation techniques can used to construct probability surfaces from these derivative datasets, and a set of optimal locations can be determined through an integrated analysis of this data. We discuss how the entire process can be automated to dynamically respond to changes in input data, the results of analyses can be visualized in 3D, and visual patterns found in data can be leveraged to correlate between fields on a regional scale and guide future exploration efforts.

This paper is significant in that it presents the 3D analytical capabilities of GIS software as it applies to E&P workflows, provides examples of customizations, and encourages exploration of 3D GIS as a technology for making better integrated decisions.
Multiple Mixing-Cell Method for MMP Calculations
Authors: Ahmadi Kaveh , Johns Russell T.
Published: September 2008

The minimum miscibility pressure (MMP) is a key parameter governing the displacement efficiency of gas floods. There are several methods to determine the MMP, but the most accurate methods are slim-tube experiments, analytical methods, and numerical simulation/cell-to-cell methods. Slim-tube experiments are important to perform because they use actual crude oil, but they are costly and time consuming. Analytical methods that use the method of characteristics (MOC) are very fast and help to understand the structure of gas floods. MOC, however, relies on finding the unique and correct set of key tie lines in the displacements, which can be difficult. Slim-tube simulation methods and their simplified cell-to-cell derivatives can be slow and their MMP estimates clouded by dispersion.

This paper presents a simple and accurate multiple mixing cell method for MMP calculations that corrects for dispersion, and is substantially faster than simulation methods. Unlike previous "mixing cell" methods, our cell-to-cell mixing model uses a variable number of cells, and is independent of gas-oil ratio, volume of the cells, excess oil volumes, and the amount of gas injected. The new method relies on robust P-T flash calculations using any cubic equation-of-state (EOS). The calculations begin with only two cells and perform additional cell-to-cell contacts between resulting equilibrium phase compositions based on equilibrium gas moving ahead of the equilibrium liquid phase. We show for a variety of oil and gas compositions that all key tie lines can be found to the desired accuracy, and that they are nearly identical to those found using analytical MOC methods. Our approach, however, is more accurate and robust than those from MOC because we do not make approximations regarding shocks along nontie-line paths, and the unique set of key tie lines converge automatically.

The MMP using our mixing cell method is estimated from four or five pressure calculations based on a power-law extrapolation of the smallest tie line to zero length. Our multiple mixing cell method can calculate either the MMP or the minimum miscibility for enrichment (MME) independent of the number of components in the gas or oil. Our approach further supports the notion that the MMP is independent of fractional flow since we obtain the same key tie lines independent of how much fluid is moved from one cell to another.
Second-order differential equations: Conditions of complete integrability
Authors: Ermakov Petrovich
Published: September 2008

nema
Jensen's functional and polynomials
Authors: Pavlovic Mirjana
Published: September 2008

We investigate some estimates of the Jensen's functional J(p) = 2?log0 |p(ei?)| d?/2?, if the polynomial p(z) has a concentration at low degrees measured by ?2- norm. We consider the constants involved, both from a theoretical and a numerical point of view.
Records in geometrically distributed words: Sum of positions
Authors: Prodinger Helmut
Published: September 2008

Kortchemski introduced a new parameter for random permutations: the sum of the positions of the records. We investigate this parameter in the context of random words, where the letters are obtained by geometric probabilities. We find a relation for a bivariate generating function, from which we can obtain the expectation, exactly and asymptotically. In principle, one could get all moments from it, but the computations would be huge.
New sufficient conditions for integral complete 3-partite graphs
Authors: Híc Pavel , Pokorný Milan , Cernek Pavol
Published: September 2008

A graph is integral if all the eigenvalues of its adjacency matrix are integers. In this paper we give sufficient conditions for complete 3-partite graphs to be integral, from which we construct infinitely many new classes of such integral graphs.
Schultz polynomials of composite graphs
Authors: Eliasi Mehdi , Taeri Bijan
Published: September 2008

nema
Synthesis of 2-{[2-(2-oxo-1-azacycloalkyl)acetamido]phenoxy}acetic acids and their activity as aminopeptidase M inhibitors
Authors: Farsa Oldřich , Dockal Milan , Kováciková Jana , Benesová Mária
Published: September 2008

A series of 9 phenoxyacetic acids substituted in the o-, m-, and p-position of benzene ring with 2-(2-oxo-1-azacycloalkyl)acetamidic moiety containing 5-7-membered ?-lactam ring was prepared by a 4-step synthetic procedure. Five selected substances of this series were tested in vitro for inhibition of porcine kidney aminopeptidase M. 2-{4-[2-(2-Oxoperhydroazepin-1-yl)acetamido]phenoxy}acetic acid exhibited the highest activity with Ki = 243.6 ?M.
Synthesis of 1-(4-phenoxyphenyl)-3-[5-(substituted aryl)-1,3,4-oxadiazol-2-yl]propan-1-ones as safer anti-inflammatory and analgesic agents
Authors: Husain Asif , Ahmad F.J. , Ajmal Mohd , Ahuja Priyanka
Published: September 2008

A novel series of 1-(4-phenoxyphenyl)-3-[5-(substituted aryl)-1,3,4-oxa- diazol-2-yl]propan-1-one was synthesized by reaction of 3-(4-phenoxybenzoyl)propionic acid with several aryl acid hydrazides in phosphorus oxychloride. The structures of the compounds were supported by IR, 1H- and 13C-NMR, MS data and elemental analysis results. These compounds were tested for their anti-inflammatory, analgesic, ulcerogenic and lipid peroxidation actions. A few compounds were found to have very good anti-inflammatory activity in the carrageenan-induced rat paw edema test, while a fair number of the compounds showed significant analgesic activity in the acetic acid-induced writhing test. These new compounds showed very low ulcerogenic action with reduced malondialdehyde content (MDA), which is one of the by-products of lipid peroxidation.
Structural features of proteins as reflected by statistical scaling laws
Authors: Pitulice Laura , Isvoran Adriana , Chiriac Adrian
Published: September 2008

Within this paper, statistical scaling laws for the radius of gyration with the residues number, the surface area with the probe radii and the back- bone length with the interval of residues for a set of 60 proteins are revealed. The proteins belong to three different structural classes: alpha, beta and alpha plus beta class (20 proteins for each) according to the SCOP database classification, which takes into account the composition in the elements of their secondary structure. The shape and the surface roughness of proteins seem to be independent of the protein content in the secondary structure elements. On the contrary, the protein packing density shows a strong correlation with this composition.
Determination of relative acidity scales for some dipolar aprotic solvents by coulometry using a hydrogen-palladium electrode
Authors: Dzudovic Radmila , Jaksic Ljiljana
Published: September 2008

A coulometric-potentiometric procedure for the determination of relative acidity scales of acetone, methylethyl ketone, methyl-isobutyl ketone and propylene carbonate is described. The range of the relative acidity scale of a solvent was determined from the difference between the half-neutralization potential of perchloric acid and that of tetrabutylammonium hydroxide. The perchloric acid was generated in situ from a hydrogen-palladium electrode in presence of sodium perchlorate or tetrabutylammonium perchlorate as the supporting electrolyte. The electrode pairs glass-SCE and (H2/Pd)ind-SCE were applied for the measurement of the half-neutralization potentials of the acid and base. A wider range of relative acidity scale of the solvents was obtained with the glass-SCE electrode pair and tetrabutylammonium perchlorate as the supporting electrolyte.
Quantitative analysis of ibuprofen in pharmaceuticals and human control serum using kinetic spectrophotometry
Authors: Mitic Snezana , Miletic Gordana , Pavlovic Aleksandra , Arsic Biljana , Zivanovic Valentina
Published: September 2008

The aim of this work was to develop a new kinetic spectrophotometric method for the determination of ibuprofen in pharmaceutical formulations. Ibuprofen was determined in an acidic ethanolic medium by monitoring the rate of appearance of 1-nitroso-2-naphthol, resulting from the displacement by ibuprofen of Co(III) from the tris(1-nitroso-2-naptholato)cobalt(III) complex. The optimum operating conditions regarding reagent concentrations and temperature were established. The tangent method was adopted for constructing the calibration curve, which was found to be linear over the concentration range 0.21-1.44 and 1.44-2.06 ?g ml-1. The optimized conditions yielded a theoretical detection limit of 0.03 ?g ml-1 based on the 3.3 S0 criterion. The interference effects of the usual excipients of powdery drugs, foreign ions and amino acids on the reaction rate were studied in order to assess the selectivity of the method. The developed procedure was successfully applied for the rapid determination of ibuprofen in commercial pharmaceutical formulations and human control serum. The unique features of this procedure are that the determination can be performed at room temperature and the analysis time is short. The newly developed method is simple, inexpensive and efficient for use in the analysis of a large number of samples.
Carbon nanotubes
Authors: Marinkovic Slobodan
Published: September 2008

Nanotubes, the last in the focus of scientists in a series of 'all carbon' materials discovered over the last several decades are the most interesting and have the greatest potential. This review aims at presenting in a concise manner the considerable amount of knowledge accumulated since the discovery of this amazing form of solid carbon, particularly during the last 15 years. The topics include methods of synthesis, mathematical description, characterization by Raman spectroscopy, most important properties and applications. Problems related to the determination of CNT properties, as well as difficulties regarding their applications, in particular scaling, which would lead to their utilization, are outlined.
Preparation of irreversible hydrocolloids to improve retention of complete dentures
Authors: Aleksov Ljiljana , Stankovic Sasa , Ajdukovic Zorica
Published: September 2008

Introduction Precise reproduction of anatomical-morphological details of dentures support on working models presupposes adequate application of modern impression materials and casting procedure, as well as minimal dimensional change of these materials. The aim of the study: experimental and clinical research is connected to irreversible hydrocolloids and the objective was to examine the most suitable consistency of the alginate as the impression mass for the purpose of improving retention of complete dentures. Material and methods This research included 35 completely toothless patients, most of who had already had complete dentures, 40-80 years of age and of both sexes. Static adhesion was measured with aery late plates made of adequate corresponding and various models depending on consistency of the irreversible hydrocolloids. Each model was cut into three parts, the cuts obtained were mutually compared, and computerized graphic charts of each section were made. Results The results of the research show that there is a greater retention force in the acrylate plates obtained on models castled on an anatomical impression base taken with irreversible hydrocolloides of solid consistency. Analysis of the results shows such quality of impressed tissues that they are practically slightly displaced by the impressions regardless of the consistency of the material impressed. Conclusion In conclusion it is pointed out that the preparation of irreversible hydrocolloides must be carried out by strictly obeying the powder-water weight ratios. The sections of the models obtained by irreversible hydrocolloides of various consistencies, that is by applying different pressures, point to minimal displacement of tissues and great differences in the retention force in favor of the compressive impression.
Proposal for magnetic/electromagnetic fields protection norms on national level
Authors: Djordjevic Drago , Rakovic Dejan
Published: September 2008

Introduction The modern life is not possible without application of magnetic/electromagnetic fields, which can be both helpful and harmful for human body. Influence of magnetic/electromagnetic fields on biological systems The non-ionizing radiation, especially magnetic/electromagnetic fields of all frequencies (0-300 GHz), can have many harmful effects on the human health that is confirmed by numerous epidemiological studies, studies with volunteers, animal studies, and in vitro studies. Proposal for magnetic/electromagnetic fields protection norms Proposal for magnetic/electromagnetic fields protection norms on national level based on the WHO Program for Environment, International Commission on Non-Ionizing Radiation Protection (ICNIRP)], and WHO International EMF Project. Conclusion Protection from harmful effects of the magnetic/electromagnetic fields is still a great problem in many countries of modern society - huge costs, impaired quality of life, and more important, damage to the human health. Numerous data and publications of harmful effects of the magnetic/electromagnetic fields represents one's country basic necessary documentation for making decisions and law documents for protection norms on national level concerning the health maintenance according to the ICNIRP normatives.
Child abuse in panic disorder
Authors: Bonevski Dimitar , Novotni Antoni
Published: September 2008

Introduction Numerous authors associate child abuse with serious long-term consequences to the general and psychological well-being in particular. Clinical research to date reveals strong correlation between childhood abuse and neglect and anxiety disorders, especially panic disorder. Material and Methods This study was conducted in order to assess the level of emotional, physical and sexual childhood abuse as well as the physical and emotional childhood neglect in 40 adult patients suffering from panic disorder, diagnosed in accordance with the 10th International Classification of Disorders diagnostic criteria, compared with the control group of 40 healthy test subjects without a history of psychiatric disorders, using the Childhood Trauma Questionnaire. The severity of the clinical manifestation in patients with panic disorder was assessed using the Panic Disorder Severity Scale. Results and Discussion There were no significant differences between the groups as to the level of sexual abuse and physical neglect, whereas in the group of patients with panic disorder, the level of physical and emotional abuse was significantly higher, with emphasis on emotional neglect. With regards to the correlation between the severity of the clinical manifestation in patients with panic disorder and the severity of suffered abuse and neglect in childhood age, significant correlation was found in the physical and emotional abuse as well as emotional neglect. There was no significant correlation in the aspect of the physical neglect and sexual abuse. Conclusion Our research underlines the importance of childhood physical abuse, and especially emotional abuse and emotional neglect in the occurrence of panic disorder later in life.