bluuebunny/crossref_metadata_2025 huggingface dataset:
Coassimetria, cocurtose e as taxas de retorno das ações: uma análise com dados em painel
Authors: Castro Junior Francisco Henrique Figueiredo de , Yoshinaga Claudia Emiko
Published: April 2012

Modelos de apreçamento de ativos têm sido um tema sob constante investigação em finanças. Desde o capital asset pricing model (CAPM) proposto por Sharpe (1964), tais modelos relacionam, geralmente de maneira linear, a taxa de retorno esperada de um ativo ou carteira de ativos com fatores de risco sistêmico. Esta pesquisa apresenta um teste de um modelo de apreçamento, com dados brasileiros, introduzindo em sua formulação fatores de risco baseados em comomentos estatísticos. O modelo proposto é uma extensão do CAPM original acrescido da coassimetria e da cocurtose entre as taxas de retorno das ações das empresas que compõem a amostra e as taxas de retorno da carteira de mercado. Os efeitos de outras variáveis, como o valor de mercado sobre valor contábil, a alavancagem financeira e um índice de negociabilidade em bolsa, serviram de variáveis de controle. A amostra foi composta de 179 empresas brasileiras não financeiras negociadas na BM&FBovespa e com dados disponíveis entre os anos de 2003 a 2007. A metodologia consistiu em calcular os momentos sistêmicos anuais a partir de taxas de retornos semanais e em seguida testá-los em um modelo de apreçamento, a fim de verificar se há um prêmio pelo risco associado a cada uma dessas medidas de risco. Foi empregada a técnica de análise de dados em painel, estimada pelo método dos momentos generalizado (GMM). O emprego do GMM visa lidar com potenciais problemas de determinação simultânea e endogeneidade nos dados, evitando a ocorrência de viés nas estimações. Os resultados das estimações mostram que a relação das taxas de retorno dos ativos com a covariância e a cocurtose são estatisticamente significantes. Os resultados se mostraram robustos a especificações alternativas do modelo. O artigo contribui para a literatura por apresentar evidências empíricas brasileiras de que há um prêmio pelo risco associado aos momentos sistêmicos.
O vento solar e a atividade geomagnética
Authors: Costa Jr. E. , Simões Jr. F.J.R. , Cardoso F.R. , Alves M.V.
Published: April 2012

Ainda existem muitas lacunas sobre a geração do vento solar e, o que se sabe, é fundamentado principalmente em observações. Isso se deve principalmente à sua complexa origem e à falta de medidas in situ nas regiões onde o mesmo é acelerado. Porém, na órbita da Terra suas características são muito bem conhecidas e constantemente monitoradas. A interação do vento com o campo magnético terrestre leva à criação de diversas regiões distintas da magnetosfera e, uma vez que as condições sejam favoráveis, leva também às chamadas atividades geomagnéticas. O estudo das variações na atividade geomagnética controlada pelas condições do vento solar se faz totalmente justificado do ponto de vista acadêmico. Do ponto de vista prático, tais variações podem, por exemplo, prejudicar o funcionamento de sistemas de solo e a bordo de satélites devido ao aumento das correntes atmosféricas e da radiação que chega até o planeta, aumentando assim a importância desse tipo de pesquisas. Esse artigo apresenta uma breve revisão de alguns dos principais efeitos da interação entre o vento solar e a magnetosfera terrestre.
Teoria quântica da informação: impossibilidade de cópia, entrelaçamento e teletransporte
Authors: Piqueira José Roberto Castilho
Published: April 2012

A idéia de desenvolver computadores cuja dinâmica obedeça às leis da Mecânica Quântica data do Ultimo quarto do seculo XX e assume, nos dias de hoje, importancia tecnológica e cientifica notável, uma vez que o uso de algoritmos quânticos se disseminou na implementação de sistemas de criptografia e, além disso, relatos de experimentos de comunicação sobre canais quânticos são cada vez mais presentes na literatura. Há, até, conjecturas sobre comportamentos quânticos em sinapses e em outros fenômenos naturais tidos como macroscópicos. Todos esses desenvolvimentos têm como base a teoria quântica da informação que, de maneira geral, pode ser considerada como uma extensão da teoria clássica devida a Shannon, considerando-se dois aspectos peculiares dos fenômenos quânticos: a incapacidade de se obter uma copia de um estado quântico e o fato de estados quânticos apresentarem uma dependencia mutua, originada na sua preparação. É desses dois tópicos que este trabalho se ocupa: sem a menor pretensão de originalidade, procura conceituar entrelaçamento (entanglement) e demonstrar o teorema da impossibilidade de copia (non-cloning theorem). Algumas aplicações são apresentadas entremeadas com relatos de ficção, cuja eventual semelhança com fatos reais sera mera coincidência.
Reavaliação e rememoração dos conceitos da mecânica geral com análises geométricas e/ou gráficas: máquinas simples. Parte II
Authors: Barbieri P.F.
Published: April 2012

O presente trabalho analisa as relações entre forças atuantes em máquinas simples ao utilizar recursos geométricos/gráficos. São revistas algumas considerações sobre máquinas simples a fim de reforçar os conceitos físicos. Algumas dessas considerações não são abordadas na literatura básica de física geral. Para completar, foram determinadas as relações de deslocamentos para as diversas máquinas através da conservação do trabalho mecânico.
Wave propagation in a non-uniform string
Authors: Dall'Agnol Fernando Fuzinatto
Published: April 2012

In this article I present the behavior of the reflection and transmission coefficients of a pulse at a joint between two strings with mass densities μ1and μ2. The joint is made of a string segment with mass density varying linearly from μ1 to μ2. It will be shown that the reflection of the pulse at the joint depends largely on the ratio between the pulse width and the length of the joint. Analogies with other physical systems such as antireflection coatings and tsunamis will be considered briefly.
Saline oscillator as a teaching experiment
Authors: Lama Lucas S. del , Mulato Marcelo
Published: April 2012

The saline oscillator consists of two aligned containers that are filled in by a pair of different solutions, exhibiting electrical potential oscillations when released. These oscillations occur due to a difference of mass density presented by the fluids and they cause varying ions flow, leading to electrical potential variations between both reservoirs. Many biological systems can be understood by this model. In this work, the saline oscillator was investigated using copper sulfate, CuSO4, and sodium chloride, NaCl, solutions, changing parameters as the diameter and length of the capillary, diameter of the internal compartment and amount of unwanted ions in the main reservoir (distillated and deionized water). The system is shown to be very useful in undergraduate teaching classes.
É possível predizer o tempo de terapia das alterações específicas no desenvolvimento da linguagem?
Authors: Puglisi Marina Leite , Gândara Juliana Perina , Giusti Elisabete , Gouvêa Maria Aparecida , Befi-Lopes Debora Maria
Published: April 2012

OBJETIVO: Explorar quais medidas poderiam predizer a persistência de alterações específicas no desenvolvimento da linguagem (AEDL) a partir da associação entre os dados do desempenho na primeira avaliação fonoaudiológica e do prognóstico terapêutico da criança. MÉTODOS: Neste estudo retrospectivo, foram analisados 42 prontuários pertencentes a crianças com diagnóstico de AEDL. As idades variavam entre 21 e 63 meses no momento da primeira avaliação fonoaudiológica, que incluiu as provas de vocabulário, fonologia, pragmática e fluência. O desempenho dos sujeitos em cada prova foi pontuado de 0 a 4, com base na gravidade das alterações, sendo a pontuação máxima a adequada para a idade. Como medida prognóstica, contabilizamos o tempo de terapia (em sessões) dos pacientes que receberam alta, foram encaminhados (o quadro havia se tornado muito leve), ou permaneceram em terapia (dificuldades persistentes de linguagem). RESULTADOS: Houve associação entre os dados da avaliação inicial (classificação normal ou levemente alterada no vocabulário e pragmática) e o prognóstico (<135 sessões terapêuticas). A variável referente ao vocabulário foi a única capaz de predizer o tempo de terapia. A classificação como grave nesta medida aumentou, em média, 112 sessões na estimativa do tratamento. CONCLUSÃO: A primeira avaliação do vocabulário pode contribuir para predizer o prognóstico terapêutico da criança. Este achado é de relevância clínica e científica para a Fonoaudiologia, visto que oferece um recurso auxiliar para a realização do prognóstico e planejamento terapêutico nos quadros de AEDL.
Herbicide Resistance: Toward an Understanding of Resistance Development and the Impact of Herbicide-Resistant Crops
Authors: Vencill William K. , Nichols Robert L. , Webster Theodore M. , Soteres John K. , Mallory-Smith Carol , Burgos Nilda R. , Johnson William G. , McClelland Marilyn R.
Published: April 2012

Development of herbicide-resistant crops has resulted in significant changes to agronomic practices, one of which is the adoption of effective, simple, low-risk, crop-production systems with less dependency on tillage and lower energy requirements. Overall, the changes have had a positive environmental effect by reducing soil erosion, the fuel use for tillage, and the number of herbicides with groundwater advisories as well as a slight reduction in the overall environmental impact quotient of herbicide use. However, herbicides exert a high selection pressure on weed populations, and density and diversity of weed communities change over time in response to herbicides and other control practices imposed on them. Repeated and intensive use of herbicides with the same mechanisms of action (MOA; the mechanism in the plant that the herbicide detrimentally affects so that the plant succumbs to the herbicide; e.g., inhibition of an enzyme that is vital to plant growth or the inability of a plant to metabolize the herbicide before it has done damage) can rapidly select for shifts to tolerant, difficult-to-control weeds and the evolution of herbicide-resistant weeds, especially in the absence of the concurrent use of herbicides with different mechanisms of action or the use of mechanical or cultural practices or both.
The Effect of Withdrawal Rate on the Uniformity of Edgewater Intrusion
Authors: Muskat M.
Published: April 2012

Calculations are reported on the differential sensitivity of the updip invasion of oil strata of varying permeability to the driving pressure differential. It is assumed that the water-oil interfaces advance with sharp fronts, or that the microscopic displacement efficiency is independent of rate and capillary pressure effects. It is found that, under such conditions, limitations of withdrawal rates will not greatly inhibit the "fingering" and bypassing tendency through high permeability strata unless the differential fluid head across the original oil column is of the order of or exceeds about 80 per cent of the driving pressure differential. In practice, such restrictions will be feasible only for oil reservoirs and aquifers of high permeability and dip, but may develop automatically under combined gas injection and water drive operations.

Introduction

A commonly expressed view regarding the intrusion of edgewaters into oil producing formations is that the geometry of such advance is rate sensitive. Specifically, it has been suggested that high rates of advance, stimulated by rapid withdrawals, will lead to "fingering" and an irregular type of invasion, whereas at low withdrawal rates the water encroachment will be more uniform. Two factors tend to support this view. One is the resultant effect of capillary pressure and gravity gradients in the displacement processes involved in water intrusion, which are magnified at low rates of flow so as to improve the recovery efficiency. The other is the direct retarding effect of the rising water head as it advances upslope into the producing area.

Capillary pressure forces give rise to a rate sensitivity of the oil recovery by water displacement in uniform strata as well as differential effects in non-uniform formations. These are basically independent of the effect of gravity and would also occur in horizontal beds or when the oil and water have the same density.
Well-Performance Relationships in Heavy-Foamy-Oil Reservoirs
Authors: Kumar R.. , Mahadevan J..
Published: April 2012

Inflow performance in some heavy-oil reservoirs is not well understood because the fluid properties differ from conventional behavior. In this work, we develop an expression for inflow performance as a function of properties of foamy oils (e.g., density, viscosity, solution gas/oil ratio, and formation volume factor). We define two parameters, the endpoint entrained-gas fraction and the apparent bubblepoint, adapted from previous studies, to account for the extent of entrained-gas fraction in the liquid. The fluid properties are modified to account for the entrained gas and then incorporated in the equations describing flow from a reservoir at pseudosteady state.

The results of our study show that the entrained gas and the apparent bubblepoint impact the fluid properties and, therefore, the inflow performance at the bottomhole conditions. In the presence of entrained gas, the density of the fluid decreases and the formation volume factor increases. Both these properties show an inflection below the bubblepoint pressure, and the solution gas/oil ratio shows a constant value until the apparent bubblepoint is reached. The inflow-performance curve, therefore, displays an inflection as opposed to the monotonically changing curve normally observed with conventional oils. The outflow-performance curve is lowered when the effect of entrained gas is included, caused by lower density; hence, the nodal systems analysis predicts a greater production rate for a foamy-oil reservoir compared with a conventional reservoir.
Determination of Active Constraints in a Network
Authors: Watts J.W.. W. , Fleming G.C.. C. , Lu Q..
Published: April 2012

There is increasing interest in modeling networks of wells, including subsurface components of complex wells and surface facilities. Such modeling requires setting constraints at various points in the network. Typical constraints are maximum phase flow rates and minimum flowing pressures. A major difficulty in network calculations is determining which of these constraints is active.

This paper presents a method that uses slack variables in determining active constraints. The linearized equations of interest generally come in pairs, with each pair consisting of a base equation and a constraint equation. The base equation is the equation that normally applies. The constraint equation replaces it if the constraint is active. Normally, only one of these two equations can be satisfied. The slack variable provides a way to ensure that both are satisfied, regardless of which is active. If the constraint is inactive, the slack variable is added to the constraint equation and accounts for the slack, which by definition is the amount by which the inactive equation is not satisfied. On the other hand, if the constraint is active, the slack variable is instead added to the base equation, and the constraint equation as originally written is satisfied. To obtain this behavior, we define a parameter w and add w times the slack variable to the base equation and (1 − w) times the slack variable to the constraint equation. Thus, if w = 1, the slack variable is added to the base equation, and the constraint is active. On the other hand, if w = 0, the slack variable is added to the constraint equation, and the base equation is active. The slack is always in the inactive equation. There is a w associated with each slack variable.

Determining the parameter w is an iterative process. The efficiency of the process is improved by manipulating the network matrix such that we can create a Schur complement that has the slack variables as its unknowns and contains the only references to the w's To determine the slack variables, we need only to work with this matrix, which typically is much smaller than the network matrix.

The resulting method is implemented within a general purpose reservoir simulator. Testing of the method in more than 700 cases has shown it to be much more robust than an earlier heuristic procedure.
Displacement Mechanism in Multi-Well Systems
Authors: Kern Loyd R.
Published: April 2012

A procedure for determining the behavior of a reservoir under a gas or water injection program was reported by Buckley and Leverett in 1942. This method, which allowed the calculation of the phase saturation distribution behind the front of a displacing fluid, has been extended to apply to a more general situation.

The reservoir may initially contain flowing quantities of the displacing fluid, or the fluid in the reservoir may be above saturation pressure so that solution effects are present. Production may occur behind the front as in the case of a well which is produced after breakthrough of the displacing fluid. The calculating procedure is simplified in that the graphical integration necessary to determine breakthrough saturation is eliminated by performing a direct integration and the graphical differentiation necessary to determine saturation distribution is eliminated by representing the displacing phase fraction of the flowing stream by an empirical equation. This representation results in simple expressions for the producing gas or water/oil ratio and cumulative production.

Introduction

A method for the calculation of the saturation distribution behind the front (interface between the displaced and displacing phases in a gas injection or water flooding operation) was reported by Buckley and Leverett in 1942. The method leads to a curve for the saturation distribution which is double-valued; consequently, part of the curve was interpreted to be physically meaningless. That part of the curve which has physical significance was determined by a graphical integration (material balance).

In this paper it is shown that the integration may be performed analytically with a resulting equation for the saturation of the displacing phase at the front. The case in which the displacing fluid is initially flowing and the case in which the reservoir is initially above the saturation pressure so that some injected gas goes into solution are included in the integration. The calculations are considerably simplified by representing the fraction of the flowing stream which is oil by an exponential function of saturation.

The method is extended to apply approximately to reservoirs in which wells located between the injection well and the front are produced. An illustrative example utilizing the methods presented is included.
A Method for Predicting the Tendency of Oil Field Waters to Deposit Calcium Sulfate
Authors: Stiff Henry A. , Davis Lawrence E.
Published: April 2012

A graphic method was developed which can be used to predict the tendency of oil field waters to precipitate calcium sulfate under a variety of conditions. Application of this method is made to the prediction of sulfate scale formation in heater treaters, boilers, oil wells, cooling systems and water injection wells.

Introduction

A solution may be said to be in equilibrium with respect to a given salt when the concentration of that salt is equal to its solubility. If for any reason the concentration of the salt is increased or its solubility decreased, the equilibrium is upset and precipitation of the salt takes place. Thus, if the concentration of a salt in a particular solution is known and its solubility can be calculated for a given set of conditions, the tendency of this salt to form a precipitate under these conditions can be predicted. Based on these principles a method has been developed for determining the tendency of oil field waters to form calcium sulfate precipitates under various conditions.

The Solubility Diagram

Calcium sulfate precipitation most frequently occurs when two waters are mixed; one containing calcium ions, and the other sulfate ions. As one of these waters is added to the other a point may be reached where the concentration of calcium sulfate is greater than its solubility, thus causing the formation of a precipitate. The solubility diagram is a graphic device for determining the location of such points, thereby making possible a prediction of the tendency of such a system to deposit sulfate scale. A similar diagram can be used to solve many other problems involving the precipitation of calcium sulfate.

Fig. 1 shows a solubility diagram representing the mixing of two waters. Water "A" contains a high concentration of sodium, magnesium, and sulfate ions together with a small amount of calcium. Water "B" contains a high concentration of calcium ions together with sodium, magnesium and a small amount of sulfate ions.
High-Resolution Reservoir Monitoring Using Crosswell Seismic
Authors: Nalonnil Ajay , Marion Bruce
Published: April 2012

Crosswell seismic is an emerging technology that provides highly detailed images of the subsurface at the reservoir scale. The technology has the potential not only to delineate complex structures, but also to monitor the effectiveness of hydrocarbon-recovery and CO2-sequestration strategies. The technique employs tomographic surveying, whereby a transmitter and receiver are deployed in separate wells. With this setup, interwell velocity profiling and structure can be obtained from direct-wave and reflection processing, respectively.

With increased hydrocarbon recovery and CO2 sequestration becoming more prominent in the oil and gas industry, the ability to monitor the efficiency of these strategies is paramount. In this paper, two case studies of crosswell seismic surveying are discussed, with the focus on high-resolution imaging and monitoring during CO2 injection for improved oil recovery. A brief description of the measurement theory and its capabilities is provided, followed by a description of the processing workflow and, finally, a discussion of the acquired results.

The two cases discussed demonstrate that crosswell seismic was able to successfully monitor the injection through velocity profiling in time lapse and provide answers as to why and how the flow has occurred through interpretation of the crosswell reflection seismic section. The results clearly show that crosswell seismic could significantly reduce the uncertainty and risk associated with injection processes for improved recovery and can extend the technique to sequestration monitoring.
The Evolution of the Role of Openhole Packers in Advanced Horizontal Completions: From Novel Technology to a Critical Key to Success
Authors: Gavioli P.. , Vicario R..
Published: April 2012

Openhole packers have been shown to be very effective in many different applications, including curing losses, controlling high-permeability zones and fractures, improving equalization in passive- and active-inflow-control-device (ICD) completions, and, most importantly, controlling water and gas production. The use of these tools has increased exponentially in the last few years and will continue to grow. This paper summarizes the most important findings and lessons learned about the role of zonal isolation in advanced horizontal completions.

More than 12 years of experience using reservoir-optimized completions, including passive or active ICDs and openhole packers, in more than 1,000 wells and several tens of different fields around the world has led to the accumulation of best practices and rules of thumb. The approach for openhole packers has changed markedly with time, along with the industry learning about the importance of these tools in advanced horizontal completions.

Important considerations have been generated to design horizontal completions under different fluid properties, reservoir uncertainties, and optimum operational considerations allowing for equalization of flow along the entire length of the horizontal section. These best practices came from extensive run history and lessons learned, and it has been found that openhole packers often play the most critical role for a completion's success. The availability of a wide range of new zonal-isolation tools makes it easier for operators to obtain the best and most-cost-effective solution for each application.

Openhole packers for compartmentalization are key for success in many applications and offer benefits for inflow and annulus flow control. An extremely important consequence is the ability to control gas or water after breakthrough. This has been proved from analyzing a significant amount of production logs post-installation. Actual well-performance data and simulations will be shown to support the discussion and illustrate concepts and findings.
Observations From Profile Logs of Water Injection Wells
Authors: Kaveler H.H. , Hunter Z.Z.
Published: April 2012

Variation of the horizontal permeability (parallel to the bedding plane) in the vertical section of reservoir rocks has long been observed as a characteristic of a normally heterogeneous system which reservoir rock represent.

The use of a recently developed water injection profile device offered opportunity to measure with a high degree of reliability the rate of inflow of water into Burbank sandstone in wells previously cored. Water injection profiles were not correlative with core permeability profiles in such wells. Apparently the vertical permeability substantially influences the flow between strata in a formation in a manner as to void the usual conclusions that have been drawn from consideration of the horizontal permeability measurements alone. The results obtained in comparing water injection profiles with horizontal permeability profiles suggest that many of the usual production operations based upon "selective" behavior or treatment of rock exposed in well bores need to be re-valuated and re-examined.

Introduction

Petroleum reservoir rock are heterogeneous systems. Heterogeneity exists in respect to lithologic character insofar as such rock are composed of distinguishable solid phases. Heterogeneity also exists in respect to certain properties, such as porosity and permeability, that vary due to variation of the physical structure of the rock. Except in exceptional cases, both the horizontal permeability (measured parallel to the bedding planes) and the vertical permeability (measured perpendicularly to the bedding planes) exhibit significant variation in any common source of supply. The variation in horizontal permeability, as reflected by core analyses, has drawn the greatest attention of petroleum technologists probably out of the general notion that the mass movement of fluids in a reservoir is predominantly in the horizontal direction. Furthermore, in the usual case, the rock permeability measured in the horizontal direction is greater than that in the vertical.
Equation-of-State Modeling for Reservoir-Fluid Samples Contaminated by Oil-Based Drilling Mud Using Contaminated-Fluid Pressure/Volume/Temperature Data
Authors: Sah P.. , Gurdial G.. , Pedersen K.S.. S. , Izwan Deraman H.. , Ramli F..
Published: April 2012

Bottomhole samples collected in wellbore systems using oil-based muds (OBMs) are likely to be contaminated by medium-to-heavy hydrocarbon fractions present in the OBM. Pressure/volume/ temperature (PVT) data measured for a contaminated fluid will not be representative for the clean reservoir fluid, and such PVT data are hence often ignored by the operator, which means loss of a considerable investment. A proper estimate of the representative clean reservoir fluid is essential for reserves estimation and facilities design. Unfortunately, no experimental methods exist for such estimations. It would be valuable for the oil industry to have options for numerical cleaning of OBM-contaminated reservoir fluids and to be able to carry out equation-of-state (EOS) modeling and regression for a contaminated composition in a way that would allow PVT data for a contaminated fluid to be corrected to represent the uncontaminated fluid. This paper describes such a methodology, which is integrated with EOS modeling procedures for numerically cleaned reservoir-fluid compositions. Thanks to this method, PVT data for contaminated samples do not have to be ignored and oil and gas operators can justify investing in PVT analyses for contaminated-fluid samples.

This paper details the process through which the available data can be used. The composition of the reservoir fluid is estimated from the composition of the fluid with a certain content of OBM contaminate, and, contrary to other proposed methods for numerical cleaning, it takes into consideration that the aromaticity of the reservoir fluid may deviate substantially from that of the OBM contaminate. A regression procedure is applied afterward using the available PVT data in order to develop ultimately an EOS model for the clean reservoir fluid. Compositional data and PVT data are presented for a real reservoir fluid contaminated with OBM. Because data are also available for the clean reservoir fluid, it has been possible to verify the validity of the suggested procedure. The numerical cleaning procedure does not require any nonstandard laboratory data, and the given method also is not restricted to any particular brand of OBM or well type.
Visual Examinations of Fluid Behavior in Porous Media - Part I
Authors: Chatenever Alfred , Calhoun John C.
Published: April 2012

An exploratory study was made to examine the possibilities of a visual approach in investigations into microscopic mechanisms of fluid behavior in porous media. Appropriate apparatus and techniques were developed so that microscopic phenomena could he recorded on color movie film as well as be observed visually. The observation flow cells in which the fluid behavior studies were made were essentially single-layered matrices of spheres between plates, sometimes all-glass, sometimes all-Lucite and sometimes a combination of the two. The fluids were limited to water and a filtered crude oil.

Two flow regimes were observed during the flow of the immiscible liquids: channel flow and slug flow. In the former, transport was effected through stable networks of interconnecting channels; and in the latter, part of the movement took place in the form of slugs. Under certain conditions, flood-front patterns were found to be different depending upon which liquids were the displacing and displaced phases and not depending upon whether the matrix was water-wet glass or oil-wet Lucite. Residual formations of oil and water were observed and are described. Some of the ramifications and significance of the observed phenomena are discussed.

Introduction

In recent years considerations of microscopic mechanisms of fluid flow in porous media have taken on greater significance. Much needs to be learned before the fundamentals of petroleum technology are completely established. For example, many unanswered questions exist in connection with relative permeability, displacement phenomena, residual fluid formations, flow structure, etc.; and further analytical mathematical formulations are seriously indicated. It is hoped that systematic investigations into the microscopic mechanisms connected with the behavior of fluids in porous media will shed some light on some of the problems extant.

Until recently microscopic mechanisms have been considered almost exclusively as speculative hypotheses. Within the past few years, however, the problem has been submitted to a limited number of experimental investigations. Nuss and Whiting made some studies on the pore-space geometry of sandstones and limestones by impregnating cores with an inert plastic and leaching the solid matrices to leave behind plastic models of the pore spaces. Schaefer traced pore spaces microscopically through lengths of limestone cores by cutting away thin sections from the exposed faces normal to the line of view.
A Technical and Economic Study of Completion Techniques in Five Emerging US Gas Shales: A Woodford Shale Example
Authors: Agrawal A , Wei Y , Holditch S.A. A
Published: April 2012

With the increased demand for energy and the declining conventional hydrocarbons worldwide, energy companies are turning to unconventional resources such as shale gas. With more than 2,000 Tcf of gas in place indentified in just 5 shale gas plays in the United States, shale-gas formations are now the number one targets for exploration drilling. Furthermore, there are still many more major shale-gas plays and basins waiting to be explored, evaluated, and developed. Because of the extremely low permeability of most shale formations, it is essential to select the appropriate completion techniques for shale-gas reservoirs. There are very few papers in the petroleum literature that provide a logical method to select completion techniques for given shale-gas-reservoir conditions. There are papers discussing successful completion techniques that seem to work for a specific shale. We have used many of these SPE papers to help define "best practices" in completing shale-gas reservoirs. We then developed logic to determine the best practice in completing shale-gas reservoirs as a function of reservoir conditions. In this paper, we will specifically cover the logic we have developed for choosing completion techniques in shale-gas reservoirs.

First, we performed a literature review on the five basins as well as on all shale-gas plays in the US to determine the best practices in shale-gas completion techniques in fluctuating price environments and identify key geologic parameters that affect overall well performance. From our literature review, we identified seven pertinent geologic parameters that influence shale-gas completion practices. Next, we identified different completion trends in the industry for different geologic settings. Subsequently, we generated an economic model and performed sensitivity analysis to determine optimal completions for each gas-shale basin. On the basis of these economic models, we developed decision flow charts to select completion techniques. Finally, we programmed the flow chart, and we call this program Shale Gas Advisor. This program can be used to determine optimum completion best practices not only for the five gas-shale basins discussed, but also for gas-shale plays that have similar geologic attributes. We validated the program with published case histories in the SPE literature.
Impacts of the Number of Perforation Clusters and Cluster Spacing on Production Performance of Horizontal Shale-Gas Wells
Authors: Cheng Y..
Published: April 2012

Multistage hydraulic fracturing has become the key technology to complete horizontal wells in shale-gas reservoirs. In each stage, multiple perforation clusters are used to create multiple transverse fractures. How these clusters are placed significantly affects both the short-term and long-term production performance of horizontal shale-gas wells. The author's previous work has demonstrated that when more than two fractures are created, mechanical interaction among fractures creates strong stress concentrations around the inner fractures. As a result, the fractures between two edge fractures (i.e., subcenter and center fractures) experience only limited dilation, and their widths are much smaller than the edge-fractures’ width.

In this paper, reservoir-simulation models were constructed by quantitatively incorporating the findings of the author's previous work to investigate the impacts of the number of perforation clusters and cluster spacing on production performance of horizontal shale-gas wells. The paper illustrates that with the same cluster spacing, the scenarios with more clusters have lower ultimate gas recovery because of the increased number of less-effective inner fractures. Given the same lateral length of a horizontal well, although reducing cluster spacing increases the total number of fractures, smaller cluster spacing does not necessarily improve well performance. Inadequate small cluster spacing can actually lead to a greater number of less-effective or ineffective fractures, and, therefore, lower gas rate and ultimate recovery.
Designing Multistage Frac Packs in the Lower Tertiary Formation–Cascade and Chinook Project
Authors: Haddad Ziad , Smith Mike , De Moraes Flavio Dias
Published: April 2012

The Cascade and Chinook Project is located in the Walker Ridge area in the Gulf of Mexico (GOM), 250 miles south of New Orleans in depths between 8,200 and 8,900 ft. The oil-producing reservoir is in the Lower Tertiary Wilcox formation, with a gross sand thickness of 1,200 ft. The reservoir midpoint is at an average depth of 25,600 ft true vertical depth subsea (TVDss), with a bottomhole pressure of 19,500 psi and a bottomhole temperature of 260°F. The reservoir comprises vertically stacked thin beds of sand and fine-grained-siltstone intervals with effectively no vertical permeability. Additional information on this project can be found in Moraes et al. (2010).

Multiple limitations were considered during the initial design phase of the frac-pack program. The fracs were designed taking into account the use of a single-trip multizone (STMZ) sand-control system. Some of these design challenges are briefly discussed by Cunha et al. (2009). Although this system was not crucial in the overall implementation of the frac program, it added additional complexity from an operational standpoint because of a continuous, multistage frac operation. Some of the operational limitations included service-tool erosion limitations because of maximum pump rates and proppant volumes, overall frac-vessel capacity, boat-to-boat fluid transfers, and crew fatigue. The geological complexities of the reservoir were another major challenge in completing this very thick interval. Perforation intervals had to be placed to avoid a fault (and thus a potential early screenout), avoid a water contact, comply with tool-spacing limitations, and still maximize contact with net pay.

This paper addresses the approach taken to develop a fracture-stimulation program for the Lower Tertiary formation in the Cascade and Chinook Project. Some of the major questions addressed during this process include the following: How many fracture treatments are needed? What is the optimum fracture geometry? What is the desired conductivity? How to effectively position the perforation intervals? What is the desired pump rate, and is a high-density fluid needed to fracture this deep, high-pressure formation? The approach, the answers, and the treatment are discussed along with responses to additional questions that arose during the actual fracturing operations.

Along with the Lower Tertiary in the GOM, the industry faces similar challenges around the world. These include reservoirs with potentially large reserves but much lower permeability (caused by depth and in-situ stresses) where fracturing is required for both stimulation and potential formation-collapse sand control. Careful planning is necessary to avoid costly learning curves in these environments.
Gas Lift Optimization Using Proxy Functions in Reservoir Simulation
Authors: Lu Q.. , Fleming G.C.. C.
Published: April 2012

Artificial lift by means of gas injection into production wells or risers is frequently used to increase hydrocarbon production, especially when reservoir pressure declines. We propose an efficient optimization scheme that finds the optimal distribution of the available gas lift gas to maximize an objective function subject to surface-pipeline-network rate and pressure constraints. This procedure is a nonlinearly constrained optimization problem solved by the generalized reduced-gradient (GRG) method. The values of objective function, constraint functions, and derivatives needed for optimization can be evaluated through two methods. The first method repeatedly solves the full-network equations using Newton iteration, which takes into account the flow interactions among wells; however, this method can be computationally expensive. The second and more efficient method is a new approach proposed in this paper. It constructs a set of proxy functions that approximates the objective function and constraints as functions of gas lift rates. The proxy functions are obtained by solving part of the network that consists of a gas lifted well or riser, assuming a stable pressure at the terminal node where the partial network is decoupled from the rest of the network, and are used to inexpensively evaluate the objective function, constraints, and necessary derivatives for the optimizer. A procedure to predict the proxy functions on the basis of previous values can be used to reduce the number of partial-network solves, and the partial-network solution has been parallelized for faster simulation. These two methods can be applied at different timesteps during the course of the simulation. The proposed methods are implemented within a general-purpose black-oil and compositional reservoir simulator and have been applied to real-field cases.
Chemical Modification of Biopolymers To Design Cement Slurries With Temperature-Activated Viscosification—A Laboratory Study
Authors: Reddy B.R.. R. , Patil R.. , Patil S..
Published: April 2012

Polymeric viscosifiers are added to cement slurries for a variety of reasons, including prevention of particle settling and control of fluid loss, gas migration, and free water. Many of these functions are critically important after the cement slurry has been placed behind the casing but before the setting of the cement. Some functions, such as particle-settling prevention, are also important during the pumping phase. Unfortunately, most of the viscosifying polymers suffer from thermal thinning at bottomhole temperatures, especially under shear. The amount of polymer required to maintain the required level of viscosity at elevated bottomhole temperatures causes excessive surface-slurry viscosification at ambient temperature. Pumping such slurries can require higher pump pressures, which, in some cases, might exceed formation breakdown pressures causing unintended fractures.This becomes a serious challenge when the window between the fracture pressure and the pore pressure of the formation is narrow. It would be a significant improvement to oilfield cementing technology to develop polymers that do not cause excessive slurry viscosification on the surface but gradually increase the slurry viscosity as it reaches downhole temperatures, with the maximum viscosity reached at the time the slurry becomes static behind the casing.

This paper describes a chemical method, not based on encapsulation, for modifying biopolymers and their derivatives—for example, hydroxyethylcellulose (HEC) and xanthan—that renders them insoluble in cement slurries at room temperature (RT). When the cement slurries containing modified HEC are heated, the slurries develop viscosity upon heating, as reflected by changes to slurry rheology with temperature. The method also provides for increased viscosification efficiency of the modified polymers because of the increased molecular weights of the modified biopolymer products. Synthesis details, slurry rheologies at different temperatures, and job-placement simulation details are presented. A possible reaction mechanism that is operative in the chemical-modification step is also discussed.
Shear Stability of EOR Polymers
Authors: Zaitoun A.. , Makakou P.. , Blin N.. , Al-Maamari R.S.. S. , Al-Hashmi A.R.. R. , Abdel-Goad M.. , Al-Sharji H.H.. H.
Published: April 2012

An experimental study of shear stability of several high-molecular-weight polymers used as mobility-control agents in EOR projects has been performed in well-controlled conditions. The shearing device was made of a capillary tube with an internal diameter (ID) of 125 μm, through which polymer solution was injected at a controlled rate. The setup enables a precise measurement of the shear rate to which the polymer macromolecule is submitted. The degradation rate was measured by the viscosity loss induced by the passage into the capillary tube. The shear rate was gradually increased up to 106 sec–1 while checking degradation rate at each stage.

Different commercial EOR polymer products were submitted to the test with polyacrylamide backbone and different substitution monomer groups. All macromolecules behave as flexible coils in solution. The parameters investigated were Molecular weight (between 6 and 20×106)Nature of substitution group (acrylate, ATBS/sulfonate, nVP/ vinyl-pyrrolidone)Salinity Polymer shear degradation increases with molecular weight and salinity, but decreases with the presence of acrylate, ATBS, and nVP. All results can be interpreted in terms of chain flexibility. The highly flexible polyacrylamide homopolymer is the most sensitive to shear degradation. Introduction of acrylate groups in the polymer chain induces some stability because of the rigidity provided by charge repulsion, which vanishes in the presence of high salinity because of the screening of acrylate negative charges. ATBS and VP groups, which are larger in size, provide significant chain rigidity, and thus better shear stability. It is also shown that some very-high-molecular-weight polymers, after passing the shearing device, attain a final viscosity lower than lower-molecular-weight products with the same chemical composition. This factor has to be taken into account in the final choice of a polymer for a given field application.

As a comparison, although less popular today than 2 decades ago, xanthan gum (XG), which behaves like a semirigid rod, is shown to be much less sensitive to the shear-degradation test than the coiled polyacrylamides (Sorbie 1991).
Reduction of Perforating Gunshock Loads
Authors: Baumann C.E.. E. , Guerra J.P.. P. , William A.. , Williams H.A.. A.
Published: April 2012

Thousands of well-perforation jobs are executed successfully around the world each month; however, certain perforation jobs require special design considerations to minimize the risk of equipment damage, such as bent tubing and unset packers, from perforating gunshock loads. Perforating guns generate pressure waves in the completion fluid and stress waves in structural components. The magnitude, duration, and timing of these waves depend on job parameters that can be adjusted by the design engineer, such as type, length, and loading of guns; number of shock absorbers; distance from sump packer to bottom of guns; and distance from completion packer to top of guns. The sensitivity of peak loads and gun-string movement to key design parameters can be evaluated with a software tool specifically developed to predict well-perforation-induced transient fluid-pressure waves and the ensuing structural loads. All relevant aspects of well-perforating events are modeled, including gun carrier filling after firing, wellbore pressure waves and associated fluid movement, wellbore pressurization and depressurization by reservoir pressure, and the dynamics of all relevant gun-string components, including shock absorbers, tubing, and guns.

Existing fast-gauge pressure data from a large number of perforation jobs were used in previous jobs to verify that predictions made by using software simulation are sufficiently accurate, both in magnitude and time; thus, the transient pressure loading on well components is sufficiently accurate to predict the structural dynamics response and the associated gun-string loads. In this paper, we present case studies that show how key elements used for gunshock mitigation are simulated, and the sensitivity of peak loads and deformation to gun-string elements, such as shock absorbers, gun types and loading, tubing size and weight, and packer placement.

With this software, we evaluate the dependence or sensitivity of peak loads and gun-string movement on/to key design parameters, and, when necessary, design changes are made to reduce potentially unsafe load conditions. The design verification and optimization methodology described in this paper significantly reduces the risk of nonproductive time and fishing operations. Key technologies described in this paper enabled the successful execution of many deepwater high-pressure (HP) perforation jobs, including Petrobras’ Cascade and Chinook, the largest deepwater HP perforation jobs performed to date in the Gulf of Mexico.