bluuebunny/crossref_metadata_2025 huggingface dataset:
Análise termogravimétrica em clones de eucalipto como subsídio para a produção de carvão vegetal
Authors: Santos Rosimeire Cavalcante dos , Carneiro Angélica de Cássia Oliveira , Trugilho Paulo Fernando , Mendes Lourival Marin , Carvalho Ana Márcia Macedo Ladeira
Published: April 2013

No Brasil, o uso da madeira, para geração de energia, tem sido relacionado à produção de carvão, em decorrência da demanda existente pelo produto junto ao setor siderúrgico e, em sua grande maioria, são espécies do gênero Eucalyptus. No entanto, em função das variações que ocorrem na qualidade da madeira do referido gênero, faz-se necessário estudá-las, pois esse fato pode ocasionar consequências negativas na qualidade e rendimento do carvão vegetal, as quais refletirão nas operações dos alto-fornos siderúrgicos. O objetivo do presente trabalho foi estudar a qualidade da madeira de diferentes materiais genéticos de eucalipto para produção de carvão vegetal por meio da análise termogravimétrica. No estudo, considerou-se à resistência a degradação térmica da madeira e as características qualitativas e quantitativas do carvão. Pelos resultados, verificou-se que os maiores picos de degradação térmica ocorreram na faixa de temperatura compreendida entre 300 e 400ºC; o material genético um foi o que apresentou a menor perda de massa total e o três foi o menos estável, tendo esses apresentado, respectivamente, maior e menor rendimento gravimétrico em carvão vegetal; todos os materiais genéticos apresentaram, de modo satisfatório, rendimento gravimétrico em carvão vegetal e qualidade dos mesmos.
Aceitação de dietas hospitalares e estado nutricional entre pacientes com câncer
Authors: Ferreira Daiane , Guimarães Tessa Gomes , Marcadenti Aline
Published: April 2013

OBJETIVO: Verificar a aceitação de dietas hospitalares, em relação ao estado nutricional, entre pacientes com câncer admitidos na Unidade de Oncologia/Hematologia de um hospital terciário. MÉTODOS: Estudo transversal conduzido entre 100 pacientes, com idade >18 anos de ambos os gêneros. Índice de massa corporal e avaliação nutricional subjetiva global produzida pelo próprio paciente foram utilizados para detecção do estado nutricional. Índice de resto-ingestão foi utilizado para avaliar a aceitação da dieta, e os motivos para não aceitação foram verificados por meio de questionário. Os dados foram expressos em médias e desvio padrão, ou medianas e percentuais. As comparações foram realizadas por meio de testes t de Student, Wilcoxon Mann-Whitney e do χ² de Pearson. RESULTADOS: No total, 59% dos pacientes eram do gênero masculino e a idade média foi de 51,6±13,5 anos. De acordo com a avaliação nutricional subjetiva global produzida pelo próprio paciente, 33% dos participantes foram considerados desnutridos e o índice de massa corporal detectou 6,3% de desnutrição. Os principais sintomas relatados foram: inapetência, xerostomia, constipação, disgeusia, náuseas relacionadas aos cheiros e saciedade precoce. O índice de resto-ingestão foi de aproximadamente 37% e significativamente maior entre os desnutridos comparativamente aos bem nutridos (58,8 x 46,4%; p=0,04). Quanto aos motivos relatados para a não aceitação da dieta oferecida, destacaram-se falta de sabor, monotonia das preparações, grandes quantidade oferecidas, falta de apetite e temperatura inadequada da refeição. CONCLUSÃO: Observou-se um elevado índice de resto-ingestão entre os pacientes com câncer, principalmente entre os desnutridos, pela avaliação nutricional subjetiva global produzida pelo próprio paciente.
Uso de moderadores de apetite entre estudantes da área da saúde na Região Sul do Brasil
Authors: Zubaran Carlos , Lazzaretti Rubia
Published: April 2013

OBJETIVO: Estabelecer a prevalência do uso de moderadores de apetite entre estudantes da área da saúde na Região Sul do Brasil. MÉTODOS: Estudantes universitários (n=300) de sete cursos da área da saúde da Universidade de Caxias do Sul completaram um questionário sobre o uso de moderadores de apetite. RESULTADOS: Uma significativa porcentagem da amostra (15%; n=45) usou moderadores de apetite pelo menos uma vez na vida. As substâncias mais comumente usadas foram drogas estimulantes (5%), incluindo amfepramona (3,3%) e fenproporex (1,7%). O uso de moderadores de apetite foi mais prevalente entre estudantes de Enfermagem (26,7%) e Nutrição (24,4%%). Não foi relatado o uso de moderadores de apetite entre estudantes de Medicina. O uso de anorexígenos foi significativamente mais prevalente entre mulheres. A maioria dos que usaram supressores de apetite o fez sob orientação médica, como também usou tais substâncias por mais de 3 meses. CONCLUSÃO: O uso durante a vida de moderadores de apetite foi significativo entre estudantes da área da saúde, especialmente entre os matriculados em Enfermagem e Nutrição. As drogas estimulantes simpatomiméticas foram os agentes mais comumente usados.
A Programação Linear na avaliação do desempenho da Saúde Bucal na Atenção Primária
Authors: Colussi Claudia Flemming , Calvo Maria Cristina Marino , Freitas Sergio Fernando Torres de
Published: April 2013

OBJETIVO: Demonstrar o uso da Programação Linear na avaliação do desempenho da Saúde Bucal na Atenção Primária. MÉTODOS: Foram utilizados os dados de 19 municípios catarinenses com mais de 50 mil habitantes que participaram de avaliação realizada no Estado em 2009. O modelo de avaliação utilizado era composto por 40 indicadores, que, depois de calculados em planilha eletrônica no Microsoft Excel 2007, foram convertidos para o intervalo [0,1], em ordem crescente (zero indicando a pior situação e 1, a melhor). Utilizando-se a técnica de Programação Linear, os municípios foram avaliados, de acordo com seu desempenho, em comparação aos demais municípios, a partir de uma curva de desempenho ótimo, denominada "fronteira de qualidade observada", de modo que a qualidade dos municípios que estavam nessa fronteira foi considerada ótima, o que não ocorreu com os demais municípios. Os indicadores foram agregados, constituindo indicadores sintéticos. RESULTADOS: Os municípios fora da fronteira de qualidade (valores diferentes de 1,0) ficaram, em sua maioria, com valores abaixo de 0,5, indicando baixo desempenho dos mesmos. O modelo aplicado aos municípios catarinenses avaliou a gestão municipal, o que implicou considerar as prioridades locais em detrimento de metas impostas por parâmetros pré-definidos. Na análise final da qualidade da Saúde Bucal na Atenção Primária, três municípios compuseram a "fronteira de qualidade observada". CONCLUSÃO: A aplicação dessa ferramenta de análise possibilitou identificar os pontos nos quais os gestores municipais devem aperfeiçoar suas ações bem como observar seu desempenho relativo e compará-lo ao de municípios semelhantes.
Redução do custo em cirurgia de coluna em um centro especializado de tratamento
Authors: Viola Dan Carai Maia , Lenza Mario , Almeida Suze Luize Ferraz de , Santos Oscar Fernando Pavão dos , Cendoroglo Neto Miguel , Lottenberg Claudio Luiz , Ferretti Mario
Published: April 2013

OBJETIVO: Comparar o custo estimado do tratamento de patologias da coluna aos verificados para esse tratamento dentro de um centro especializado. MÉTODOS: Foi realizada a avaliação dos custos médios de tratamento de 399 pacientes encaminhados por uma fonte pagadora para avaliação e tratamento no Centro de Referência de Tratamento da Coluna Vertebral do Hospital Israelita Albert Einstein. Todos os pacientes apresentavam indicação de tratamento cirúrgico antes de serem encaminhados para avaliação. Do total de pacientes encaminhados, apenas 54 foram submetidos a tratamento cirúrgico e 112 a tratamento conservador com fisioterapia motora e acupuntura. Os custos dos dois tratamentos foram calculados com base em uma tabela previamente acordada de valores de reembolso para cada etapa do tratamento. RESULTADOS: Os pacientes tratados de forma não cirúrgica apresentaram custo médio de tratamento de R$ 3.245,16, enquanto os pacientes tratados com cirurgia apresentaram custo médio de R$ 36.590,16. O custo total estimado da coorte de pacientes tratados foi de R$ 2.339.326,09, o que representa uma diminuição de 158,5% em relação ao custo total projetado desses mesmos pacientes, caso fosse realizada a indicação inicial de tratamento. CONCLUSÃO: O tratamento realizado dentro de um centro especializado em tratamento de patologias da coluna apresenta, globalmente, custos menores do que os observados regularmente.
Epífitas vasculares: histórico, participação taxonómica e aspectos relevantes, com ênfase na Mata Atlântica
Authors: Kersten Rodrigo de Andrade
Published: April 2013

O Dossel é um ecossistema complexo e ecologicamente diverso, possuindo espécies, nichos e processos próprios. Dentre as diversas formas de vida que o compõem, destaca-se a epífita. Este trabalho procurou reunir informações sobre esta sinúsia estabelecendo padrões florísticos para as epífitas no bioma Mata Atlântica. A maioria das epífitas é monocotiledônea (63,5%), seguida das Monilophyta (16,4%), Eudicotiledôneas (14,1%), Magnoliídeas (4,5%) e Lycophyta (1,6%). As famílias mais ricas são Orchidaceae com 45,8 % das espécies, Bromeliaceae com 12,9%, Polypodiaceae, com 5,5%, Araceae, com 5,0% e Piperaceae, com 4,7%. O bioma inteiro suporta, possivelmente, até cerca de 3.300 espécies, 69% das quais observadas em zonas ecotonais, 60,6% na Floresta Ombrófila Densa, 42,4% nas Formações Edáficas de Primeira Ocupação, 25,5% nas Florestas Estacionais e 22,5% na Floresta Ombrófila Mista. São ainda apresentadas sessões sobre histórico dos estudos sobre epífitas, composição taxonômica, importância ecológica, distribuição geográfica, classificação, evolução e estratégias adaptativas e distribuição espacial, contendo revisão bibliográfica atualizada sobre estes assuntos.
Estrutura da comunidade de macrófitas aquáticas em três lagoas do Parque Estadual do Rio Doce, Minas Gerais, Brasil
Authors: Ferreira Fernando Alves , Mormul Roger Paulo , Pedralli Gilberto , Pott Vali Joana , Pott Arnildo
Published: April 2013

As macrófitas aquáticas colonizam, em diferentes graus, a maioria dos ecossistemas lóticos e lênticos. Apesar da distribuição das macrófitas nas margens de lagos constituir um exemplo clássico de zonação, não existe acordo quanto aos fatores determinantes desse fenômeno. O presente trabalho teve por objetivo analisar a diferença na cobertura vegetal de três lagoas do Parque Estadual do Rio Doce; determinar se ocorre ou não sucessão de espécies na cobertura vegetal; e avaliar a distribuição das formas de vida e das espécies ao longo do gradiente de profundidade para cada lagoa. A composição da cobertura vegetal diferiu entre as lagoas estudadas. Contudo, apenas as lagoas Gambazinho e Preta apresentaram diferenças significativas entre si, enquanto a lagoa Dom Helvécio não diferiu das demais. Dessa forma, os resultados obtidos sugerem que cada lagoa constitui uma "ilha" em termos de diversidade, uma vez que muitas espécies ocorreram em apenas uma lagoa. A diversidade beta temporal apresentou uma substituição média de 70% das espécies e o principal fator que estruturou a comunidade de macrófitas nas lagoas estudadas foi o gradiente de profundidade.
Espécies de Parmotrema (Parmeliaceae, Ascomycetes liquenizados) com ácidos graxos ou atranorina medulares do litoral centro-sul do Estado de São Paulo
Authors: Marcelli Marcelo Pinto , Benatti Michel Navarro
Published: April 2013

O levantamento das espécies pertencentes aos gêneros de grandes parmélias do litoral centro-sul do Estado de São Paulo revelou a ocorrência de quatro espécies de Parmotrema A. Massal. com ácidos graxos medulares (P. ciliiferum, P. cf. cryptoxanthoides, P. melanothrix e P. praesorediosum) e uma com atranorina medular (P. mordenii). São apresentados chave de identificação, descrições detalhadas, comentários e ilustrações baseadas no material coletado.
Relação entre taxa de elocução e descontinuidade da fala na taquifemia
Authors: Oliveira Cristiane Moço Canhetti de , Broglio Gabriela Aparecida Fabbri , Bernardes Ana Paula Lazarin , Capellini Simone Aparecida
Published: April 2013

OBJETIVO: Correlacionar a taxa de elocução com as rupturas da fluência em pessoas com taquifemia e comparar com pessoas sem taquifemia. MÉTODOS: Participaram dessa investigação 14 indivíduos na faixa etária de 8 a 40 anos e 11 meses de idade, de ambos os gêneros, divididos em dois grupos pareados por idade e gênero. O GI foi composto por sete pessoas com taquifemia e o GII por sete pessoas sem taquifemia. Um protocolo de avaliação da fluência da fala foi utilizado para obter e analisar a amostra de fala, que considera a frequência das disfluências e a taxa de elocução. RESULTADOS: Os dados indicaram que quanto maiores os fluxos de sílabas e de palavras por minuto, maior o número de rupturas na fala, tanto nas pessoas com taquifemia como nas pessoas sem taquifemia. Quanto à comparação entre os grupos, houve correlação tanto para sílabas por minuto como para palavras por minuto apenas no grupo de pessoas sem taquifemia. CONCLUSÃO: O grupo de taquifêmicos apresentou aumento na taxa de elocução e disfluências comuns excessivas. Nos dois grupos analisados ocorreu uma tendência em se obter maiores valores de disfluências comuns à medida que a taxa de elocução aumentava. Porém, na análise comparativa entre o grupo de pessoas com e sem taquifemia, a correlação foi significativa apenas no grupo de pessoas sem taquifemia.
Considerando a responsividade: uma proposta de análise pragmática no espectro do autismo
Authors: Miilher Liliane Perroud , Fernandes Fernanda Dreux Miranda
Published: April 2013

OBJETIVO: Comparar o perfil pragmático das iniciativas de comunicação e o perfil bidimensional envolvendo os aspectos de iniciativa e responsividade. Além disso, buscou-se analisar os tipos mais comuns de resposta apresentadas pelos indivíduos pesquisados. MÉTODOS: Foram analisadas trinta gravações de terapia fonoaudiológica, nas quais as terapeutas interagiam com crianças do espectro do autismo (média de idade: 9 anos e 6 meses). As filmagens foram transcritas e os dados derivados foram analisados quanto ao número de atos comunicativos, à ocupação do espaço comunicativo e ao uso dos meios verbal, vocal e gestual nas iniciativas e no total de participações (iniciativas e respostas). As respostas apresentadas foram qualificadas como: não resposta, resposta adequada, resposta inadequada e resposta pragmaticamente inapropriada. RESULTADOS: Houve diferença na comparação entre as iniciativas e o total de participações no que concerne à ocupação do espaço comunicativo e no total de atos. Quanto às respostas, houve diferença no número de respostas adequadas. CONCLUSÃO: Os resultados evidenciaram a necessidade de considerar o perfil bidimensional de comunicação e ressaltaram a necessidade de qualificar as respostas a fim de discriminar as habilidades comunicativas da criança.
Feasibility studies for irrigation development in Ethiopia
Authors: Clark Alan K. , Ratsey John , Wood Robin P. H.
Published: April 2013

Ethiopia is planning to expand irrigated agriculture to help support its rapidly growing population and reduce its dependency on the import of sugar. The World Bank financed the Ethiopian Nile irrigation and drainage feasibility studies. The largest of the areas studied was in the Upper Beles river basin where water availability was substantially augmented by the completion, in May 2010, of the Tana Beles hydroelectric tunnel scheme which diverts water from the Tana basin. This paper focuses on the Upper Beles scheme and describes the creation of a digital elevation model from stereoscopic satellite imagery, the planning process used to delineate irrigation command areas (including irrigation and drainage layouts) and detailed engineering studies, including an assessment of the operating environment and challenges facing scheme operators. Social and environmental considerations were integrated in the proposed development, both in the planning process and in the identification of mitigation measures. The project team looked at irrigation schemes in Ethiopia and tried to build on successes to ensure informed recommendations were given in the feasibility study.
Female elk contacts are neither frequency nor density dependent
Authors: Cross P. C. , Creech T. G. , Ebinger M. R. , Manlove K. , Irvine K. , Henningsen J. , Rogerson J. , Scurlock B. M. , Creel S.
Published: April 2013

Identifying drivers of contact rates among individuals is critical to understanding disease dynamics and implementing targeted control measures. We studied the interaction patterns of 149 female elk (Cervus canadensis) distributed across five different regions of western Wyoming over three years, defining a contact as an approach within one body length (∼2 m). Using hierarchical models that account for correlations within individuals, pairs, and groups, we found that pairwise contact rates within a group declined by a factor of three as group sizes increased 33‐fold. Per capita contact rates, however, increased with group size according to a power function, such that female elk contact rates fell in between the predictions of density‐ or frequency‐dependent disease models. We found similar patterns for the duration of contacts. Our results suggest that larger elk groups are likely to play a disproportionate role in the disease dynamics of directly transmitted infections in elk. Supplemental feeding of elk had a limited impact on pairwise interaction rates and durations, but per capita rates were more than two times higher on feeding grounds. Our statistical approach decomposes the variation in contact rate into individual, dyadic, and environmental effects, and provides insight into factors that may be targeted by disease control programs. In particular, female elk contact patterns were driven more by environmental factors such as group size than by either individual or dyad effects.
A Fully Coupled Multiphase Multicomponent Flow and Geomechanics Model for Enhanced Coalbed-Methane Recovery and CO2 Storage
Authors: Wei Zhijie , Zhang Dongxiao
Published: April 2013

Enhanced coalbed-methane (ECBM) recovery by the injection of CO2 and/or N2 is an attractive method for recovering additional natural gas resources, while at the same time sequestering CO2 in the subsurface. For the naturally fractured coalbed-methane (CBM) reservoirs, the coupled fluid-flow and geomechanics effects involving both the effective-stress effect and the matrix shrinkage/swelling, are crucial to simulate the permeability change and; thus gas migration during primary or enhanced CBM recovery. In this work, a fully coupled multiphase multicomponent flow and geomechanics model is developed. The coupling effects are modeled by introducing a set of elaborate geomechanical equations, which can provide more fundamental understanding about the solid deformation and give a more accurate permeability/porosity prediction over the existing analytical models. In addition, the fluid-flow model in our study is fully compositional; considering both multicomponent gas dissolution and water volatility. To obtain accurate gas solubility in the aqueous phase, the Peng-Robinson equation of state (EOS) is modified according to the suggestions of Søreide and Whitson (1992). An extended Langmuir isotherm is used to describe the adsorption/desorption behavior of the multicomponent gas to/from the coal surface.

With a fully implicit finite-difference method, we develop: a 3D, multiphase, multicomponent, dual-porosity CBM/ECBM research code that is fully compositional and has fully coupled fluid flow and geomechanics. It has been partially validated and verified by comparison against other simulators such as GEM, Eclipse, and Coalgas. We then perform a series of simulations/investigations with our research code. First, history matching of Alberta flue-gas-injection micropilot data is performed to test the permeability model. The commonly used uniaxial-strain and constant-overburden-stress assumptions for analytical permeability models are then assessed. Finally, the coupling effects of fluid flow and geomechanics are investigated, and the impact of different mixed CO2/N2 injection scenarios is explored for both methane (CH4) production and CO2 sequestration.
Application of Reservoir-Centric Stimulation Design Tool in Completion Optimization for Eagle Ford Shale
Authors: Kanneganti K. T. , Oussoltsev D. , Grant D. , Ball N. , Offenberger R. M.
Published: April 2013

Completion design for unconventional shale plays in North America is a topic of high current interest. Although the practice of stimulating shale horizontal wells with large slickwater treatments is slowly changing to the use of Hybrid/Crosslink treatments in certain plays, little has changed with the method of completion design itself. Most laterals are completed using a ‘cookie cutter’ approach in which the number of stages and clusters, cluster spacing and other design parameters are based on statistics, past experience, rules of thumb or client shared knowledge, and are not tuned to the specific conditions in a particular well.

This paper presents a case study from the Eagle Ford Shale and describes a step-by-step workflow to simulate hydraulic fractures using a state of the art, reservoir-centric stimulation design tool (RCSD). The presented approach incorporated petrophysical data acquired in a vertical pilot hole with horizon interpretation, a discrete fracture network (DFN) model conditioned by seismic interpretation, image log data from a horizontal well, and completion data into a hydraulic fracture simulator. Simulation of fracture geometry was performed stage-by-stage in the RCSD tool using the recently developed unconventional fracture model (UFM), which is optimized specifically for complex fracture networks. The modeled fracture network was calibrated to microseismic events via fluid rheology and fluid loss variables while also accounting for a stress shadowing effect.

The output of the simulator includes a list of parameters such as fracture surface area, fracture propped surface area, and hydraulic fracture network geometry that can be used for the determination of estimated stimulated volume (ESV) as well as inputs into reservoir simulation for production history matching and forecasting. Also, this application of the RCSD tool in the Eagle Ford Shale provides an ability to test most aspects of the completion design by modeling stimulated volume change with respect to pumping schedule and completion parameters.
How Much Can You Extend the Reach of Coiled Tubing in Horizontal Wells Using Pressure-Hammer/Pulsing Tools
Authors: Guo Boyun , Li Jun , Feng Yin
Published: April 2013

Coiled Tubing (CT) has been widely used in well drilling, completion and work over operations. A characteristic challenge with CT is its inability to reach far in horizontal wells. As the lateral length extends, CT's stability to reach working depth decreases due to friction. Excessive friction causes work string lock-up and motor stall. The pulse pressure generated by hammer/pulsing tools has been proven to help change the CT from static to dynamic friction, resulting in extended-reach capability. It is not clear as how much can the hammer/pulsing tools extend the reach of CT in horizontal wells. This creates a gap between the design and application of the tools. This paper fills the gap.

An analytical model was developed in this project to predict the extended reach of CT in horizontal wells. The model considers pressure-induced piston effect, ballooning effect, and buckling effect on the elongation/shortening of the work string. The time-dependent elongation/shortening can change the work string from static to dynamic condition. Due to the fact that the dynamic friction coefficient is less than the static friction coefficient, it is expected that the released friction force would be translated to the extended reach of the CT string. Model analyses show that the elongation/shortening of CT string for a given CT/well/hammer condition is negligible in a certain range of depth, meaning that the given hammer/pulsing tool will not work in this range of depth. This theory is found consistent with data from wells with hammer/pulsing tool installations. This paper provides well drilling and completion engineers a handy technique to select hammer/pulsing tools for their applications in CT operations.
Drainage Against Gravity: Factors Impacting the Load Recovery in Fractures
Authors: Parmar Jaskaran S. , Dehghanpour Hassan , Kuru Ergun
Published: April 2013

Horizontal wells in the tight reservoirs are stimulated using multistage hydraulic fracturing. The fracturing fluid used in this operation is generally water based. A very low percentage of fracturing water is recovered during the flowback operation. Non-recovered water can block the gas flow and damage the reservoir. The water recovery in propped fractures is controlled by microscopic displacement efficiency and fracture areal sweep efficiency. Microscopic displacement efficiency is mainly controlled by capillarity, and has been studied extensively. Areal sweep efficiency during water drainage in propped fractures is controlled by mobility ratio and displacement direction relative to gravity direction, which needs further investigation.

This paper reports various fracture drainage experiments to understand the effect of gravity, surface properties, and viscosity on fracture sweep efficiency and total load recovery. A visual cell was built to model a propped fracture. Glass beads were packed in the space between two glass plates, and the pack was then saturated with the fracturing fluid. This simulates the initial conditions before opening the well for flowback. For simulating the water drainage against gravity, representing a fracture element below the horizontal well, the gas was injected at the bottom of the cell. Four sets of experiments were conducted to study the effect of injection pressure, interfacial tension, wettability, and fluid rheology on sweep efficiency and load recovery. Glass beads were chemically treated to alter their wettability from hydrophilic to hydrophobic. For each test, normalized fluid recovery was obtained by measuring the mass of produced fluid and using the material balance. The cell was kept in a dark room in front of a light box, and pictures were taken at regular time intervals. These images were later used to compare the drainage patterns. The results suggest that water recovery in an upward displacement very low mainly due to poor sweep efficiency. Increasing the injection pressure does not improve water recovery. Reducing surface tension and using treated hydrophobic sand improves the sweep efficiency and in turn the load recovery.
Modeling of Supercritical Fluid Adsorption on Organic-Rich Shales and Coal
Authors: Clarkson C. R. , Haghshenas B.
Published: April 2013

An important component of hydrocarbon storage in coalbed methane and organic-rich shales is sorption within organic matter. Natural gas sorption isotherms measured in these systems may include a combination of adsorption onto the internal surface area and absorption within the organic matter. The focus of the current work is the modeling of adsorbed fluids.

There have been multiple models proposed for modeling single- and multi-component adsorption on coal and shale, of which the most popular remain the simple Langmuir model and its extension to multi-components. In this work, we first review various approaches used for modeling adsorption on coal and organic-rich shale, including newer approaches such as the 2D Equation-of-State (2D-EOS) method. We discuss extensions of simple approaches, such as the Langmuir and Dubinin- Radushkevich (D-R) equations, to modeling supercritical, single-component fluids. The applications of these models to coal and shale datasets will be demonstrated. An important finding of the current work is that the simple Langmuir/D-R models are mostly adequate for modeling supercritical, single-component adsorption on coals and shales, provided that certain adjustments are made to account for supercritical fluid properties, such as adsorbed-phase density. The 2D-EOS model was found to be superior for modeling high-pressure CO2 excess adsorption on shale, however.

Several multi-component adsorption models are used to predict binary component adsorption (CH4-CO2) on shale and to investigate CO2 selectivity over CH4 for two shale systems as a function of pressure and gas composition. This information is useful for designing enhanced recovery operations in dry shale. A dataset containing heavy hydrocarbon adsorption on shale was also examined to determine the importance of adsorption in "liquid-rich" systems. The change in selectivity of heavier hydrocarbons with addition of CO2 was examined using binary gas adsorption modeling; it was found that CO2 could reduce heavy hydrocarbon component selectivity which provides a possible mechanism for enhanced recovery.
Modeling Vertical Multifractured Wells in Vaca Muerta Shale Oil Play, Argentina
Authors: Monti Luciano J. , Suarez Mariano I. , Thompson Anthony R. , Vega Leonardo
Published: April 2013

Oil production from the unconventional Vaca Muerta play is increasing as a result of a rigorous appraisal and exploitation strategy. Multiple wells have already demonstrated the potential of the Neuquén Basin, however optimization is still ongoing to determine the best practice for completing wells.

A stand out difference of the Vaca Muerta play is its thickness (100 m to 450 m), as such a development strategy based solely on vertical wells is being considered in addition to the horizontal well strategy more commonly applied in other shale plays.

The thickness of the Vaca Muerta formation creates new challenges and opportunities due to the stratigraphic variation in petrophysical and mechanical properties which can affect fracture effectiveness and well productivity. Completion design, geology and production performance need to be linked. Specifically, the geology of the Vaca Muerta formation, as is the case in most reservoirs, varies significantly more in the vertical direction in comparison to the horizontal direction. With optimum solutions not necessarily being intuitive, numerical simulation is critical as it enables a large number of variables to be analyzed and their individual impact understood and quantified.

The objective of this paper is to present the four different approaches that have been used to build numerical models to represent the vertical wells in Vaca Muerta.

These are: A single layer model with a planar fracture placed in a zone of improved permeability to represent the Stimulated Rock Volume (SRV) which is then surrounded by undisturbed matrix.A multilayer model with multiple planar fractures placed in an undisturbed matrix.A multilayer model with multiple planar fractures (one per stage), the SRV surrounding the fractures and the undisturbed matrix behind it.A multilayer model, where the SRV is modeled within a dual porosity model.

This work shows how these models were constructed, the measurements that were honored and the estimation and justification of values assumed for unknown parameters. The impact of the different methodologies on the time taken and quality of the history match obtained and subsequent forecasts is also discussed.

YPF has collected an extensive data set including PLTs, microseismic surveys, downhole pressure gauges, and pressure build ups, which has been used to constrain the numerical models. Building and history matching these models has been challenging but enables conclusions to be made about rock, fluid and completion interaction that cannot be obtained otherwise. The simpler models, have in some cases, enabled rapid estimates to be made for EUR which have subsequently been supported by the results from the more detailed modeling approaches.
Effect of Shear Rate on the Activity of Enzymes Used in Hydraulic Fracture Cleanup of Tight Unconventional Reservoirs
Authors: Barati Reza , Ouyang Chris
Published: April 2013

Injection of high or low concentration polymeric solutions in order to propagate a fracture and distribute proppants to keep the fracture open is a common practice in hydraulic fracturing of unconventional tight formations. In addition to the propagation of a main fracture, low concentration polymeric fluids open the already existing network and extend the network connected to the main fracture. Considering the very low permeability of the formation and small width of the fractures in the network, and also considering the importance of fracture cleanup and effective length during the production phase, using low concentrations of breakers is recommended to degrade the more concentrated polymeric fluid and increase the conductivity of the fracture.

Enzymes have been used successfully as breakers for fracturing fluids for many years. Enzymes are polymer specific, environmentally benign, easy to handle, miscible in the fluid, equipment friendly and not consumed because they act as catalysts. These properties make enzymes much more attractive than the oxidizer class of breakers. Enzymes are known to be temperature and pH sensitive and their properties under the targeted temperature, pH and shear rate must be measured.

In this study, the effect of high shear rates, applied during the injection of hydraulic fracturing fluids, on the activity of enzymes was studied. Enzyme activity was measured using a viscometric assay. Reversibility of changes in the activity of enzyme was studied by first shearing the polymer-enzyme mixture at high shear rates; then reducing the shear rate after a certain time, and finally comparing the activity with the activity of the same concentration of enzyme with lower shear rate history. Moreover, the effect of changes in the shear rate on the shear sensitivity of enzymes was investigated for a wide range of shear rate and polymer concentration.

Understanding the shear sensitivity of enzymes will improve the fracturing fluid injection condition. This will assure the activity of the enzymes after reaching the fracture and the more efficient cleanup of the fracture(s).
Forecasting Well Performance in a Discontinuous Tight Oil Reservoir Using Artificial Neural Networks
Authors: Bansal Y. , Ertekin T. , Karpyn Z. , Ayala L. , Nejad A. , Suleen Fnu , Balogun O. , Liebmann D. , Sun Q.
Published: April 2013

Improving the economics of the production and development of an unconventional reservoir system is a key to meeting increased demand for hydrocarbons in the near future. In general, reservoir development is vastly assisted by using hard-computing models to evaluate the potential of the formation. These models have been used to identify infill drilling locations and forecast production. However, preparing the simulation models for discontinuous tight oil reservoir systems poses a challenge with hard-computing protocols. This paper discusses a methodology developed to depict the production characteristics of a reservoir via the geological properties of the reservoir. The methodology discussed in the paper is time efficient and is proven to generate effective results.

The methodology discussed in the paper utilizes Artificial Neural Networks (ANN) to map the existing complex relationships between seismic data, well logs, completion parameters and production characteristics. ANNs developed in this work are used to forecast oil, water and gas cumulative production for a two year period. The results obtained are also extended to identify potential infill drilling locations. This work enables the practicing engineer and the geoscientist to analyze an entire reservoir in a time efficient manner.

The workflow is demonstrated on a discontinuous tight oil reservoir located in West Texas. The results discussed in the paper show the robust nature of the methodology. The workflow also helps in improving the resolution of the production surfaces which help in identifying productive, yet undrilled, locations in the reservoir. The production surface for the entire field is forecasted within a one minute time frame (~6600 locations). The method developed will help in avoiding low producing wells prior to drilling, and thus, is expected to help in the economic development of complex tight oil reservoirs.
Beyond Linear Analysis in an Unconventional Oil Reservoir
Authors: Peng Ye , Lifu Chu , Iwan Harmawan , Mark Williams
Published: April 2013

Current linear analysis is based upon the tri-linear model, which assumes a continuous and homogeneous porous medium within each flow region. This recent study, however, reveals that a discontinuous stimulated reservoir volume (SRV) is extensively associated with horizontal wells with fewer frac stages and/or within areas with high-stress anisotropic ratio. To characterize such isolated SRV scenarios, three parameters—fracture half-length, SRV permeability, and the half-width for each isolated SRV—must be inferred from the analysis, which creates a difficult challenge for the existing rate transient analysis (RTA) procedure. This paper presents a new RTA methodology and associated diagnostic plots to infer all three parameters simultaneously using the information beyond the linear flow period. The analyzed results illuminate optimizing the number of frac stages and well spacing.

The newly developed "beyond linear analysis" procedure has been used successfully to analyze more than 100 Bakken wells with various completion types and frac stages. The resultant RTA-derived statistics have been used for the construction of type curves, well history matching, completion assessments, and optimal well spacing.

Almost all the wells with fewer than 20 frac stages show an isolated SRV around each hydraulic fracture; these are good candidates for refrac. Although a high number of frac stages (e.g. >30 stages) will boost the initial production rate (IPR) and more quickly deplete the SRV, it is our conclusion that the estimated ultimate recovery (EUR) is not significantly enhanced beyond a certain number of frac stages. Moreover, both the incremental SRV and flow capacity associated with each additional stage steadily decrease. This suggests that there is an optimum number of frac stages and wells that maximize both the IPR and the EUR of a drilling spacing unit (DSU).

This new RTA methodology allows, for the first time, detailed SRV and fracture description. The precise RTA model not only greatly relaxes the dependency on compaction and PVT properties suppression during the history match, but also clarifies the "stress shadow effect" from adjacent stages and the relationship between the shear fracture displacement/dilation and inter- stage intervals.
Seismic-Based Heterogeneous Earth Model Improves Mapping Reservoir Quality and Completion Quality in Tight Shales
Authors: Suarez-Rivera R. , Dahl G. V. , Borgos H. G. , Paddock D. R. , Handwerger Schlumberger D.
Published: April 2013

This paper demonstrates the value of seismic data to define heterogeneous earth models for tight shales, improve reservoir quality and completion quality mapping, and to guide decisions of wellbore placement and completion design. The process includes quantitative classification of rock units at log-scale, definition of sample locations for laboratory testing, characterization of all dominant rock classes, and development of core-to-log transforms for all measured properties. The process also includes classification of the seismic data, based on the log-derived model, and development of class by class rock physics models for populating measured properties across the seismic volume. The quantitative relationship between core, log and seismic measurements allows population of the seismic model with complex properties. The result is a Heterogeneous Earth Model with rock classes representing the large-scale heterogeneity of the geologic system, and rock properties that characterize the behavior of each of the classes. By defining the variability of groups of properties representing reservoir quality and completion quality across the seismic cube, one can map changes in them and use this information to define reservoir potential, landing points and completion design. A case study from the Haynesville field is presented.

Conventional seismic analysis methods generally lack the ability to account for the heterogeneous nature of tight shale systems. Consequently they can provide predictions of properties that while representing the mean behavior of the system, may have a significant error at a local level. Additionally, conventional analysis is often based on rock physics models that are limited to acoustic stimuli, and fail to relate many of the complex factors that influence unconventional reservoir and well performance.

The method presented here is applicable to heterogeneous, organic-rich, oil and gas mudstone systems. Results lead to a well characterized Heterogeneous Earth Model, significantly improved mapping of variability in reservoir quality and completion quality, and better assessment of the opportunities and problems for exploration and long-term field development. This has already resulted in successful application by an operator in the Haynesville/Bossier formations in NW Louisiana, USA.
Variable Stimulated Reservoir Volume (SRV) Simulation: Eagle Ford Shale Case Study
Authors: Suliman B. , Meek R. , Hull R. , Bello H. , Portis D. , Richmond P.
Published: April 2013

Production data analysis and reservoir simulation of the Eagle Ford shale are very challenging due to the complex characteristics of the reservoir and the fluids. Eagle Ford reservoir complexity is expressed in the enormous vertical and horizontal petro-physical heterogeneity, stress-sensitive permeability, and existence of multi-scale natural fracture and fault systems. This complexity makes the prediction of the geometry and conductivity of the hydraulic fracture resulting from the stimulation process rather challenging. On the other hand, reservoir fluid complexity is demonstrated in multi-phase flow, liquid loading in the wellbore, condensate banking, etc. Based on this complexity, 3D reservoir modeling and numerical simulation have the relative advantage of addressing irregular fracture geometry, variable SRV, and multi-phase flow aspects. The South Texas Asset Team at Pioneer Natural Resources is establishing a workflow for dynamic reservoir modeling that can integrate all reservoir/wellbore parameters (formation evaluation, drilling, completion, stimulation, pre-/post-fracture surveillance, and well performance data) in order to address key questions relating to field development; such as depletion efficiency, drainage area, wells interference, and condensate banking effects. In this paper, a case study is presented to demonstrate the integration of various measurements and surveillance data to build a variable SRV reservoir model. The variable SRV model described here has the following building blocks: 1) Formation evaluation: included all the reservoir characterization data derived from logs and 3D seismic inversions and structural attributes. 2) Surveillance data integration: microseismic data (backbone for this work) are integrated with chemical and radioactive tracer logs. 3) Well performance data integration: Production data is used to determine different flow regimes during the well history and to set bounds for stimulation parameters, such as fracture half-length and permeability (Xƒ√k). 4) Numerical simulation: Micro-seismic attributes (density and magnitude) are converted to a permeability model after being calibrated with tracer logs and production flow regime parameters (Xƒ√k). PVT data is matched against an Equation of State (EOS) and input into the model.

Production data history matching, sensitivity and forecasting indicate the following: a) The SRV created by fracture stimulation has permeability fading away from the wellbore; b) Fracture geometry is variable and results in an irregular drainage area along the lateral; C) Onset of condensate banking near wellbore and along the fracture(s) can occur within the first year of production if draw down is not managed properly.
Counting Chickens before They are Hatched: An Examination of Student Retention, Graduation, Attrition, and Dropout Measurement Validity in An Online Master's Environment
Authors: Haydarov Rustam , Moxley Virginia , Anderson Dawn
Published: April 2013

This article examines definitions, rationales, and calculations associated with higher education performance measures: persistence, retention rate, attrition rate, drop-out rate, and graduation rate. Strengths and limitations of these measures are scrutinized relative to online master's programs. Outcomes of a sample of students ( N = 96) enrolled in multi-university online master's programs sponsored by Great Plains IDEA are tracked over six years. The students' unique characteristics and degree completion patterns suggest modifying performance metrics and increasing the tracking time. The study empirically proves that existing graduation and retention metrics used to compare online to face-to-face programs underreport successful outcomes for online master's students by at least one-third. Such comparisons should be made with caution, using consistent terminology and recognizing the limitations of existing metrics. Standard methods for measuring student persistence in master's degree programs should be universally established at the policy level.
Educational Persistence: Self-Efficacy and Topics in a College Orientation Course
Authors: Brewer Susan A. , Yucedag-Ozcan Arfe
Published: April 2013

This study examines whether a college orientation course for online programs leads to increased self-efficacy and, if so, which course topics are related to changes in students' self-efficacy. The culminating research question explores whether self-efficacy is related to enrollment persistence. Students' self-efficacy scores improved significantly after taking the orientation course, as measured with a general self-efficacy instrument. In particular, three course topics—characteristics of leadership, personal learning styles, and applying reading comprehension techniques—explained the variance in post-self-efficacy scores at statistically significant levels. For predicting persistence, a model encompassing three topics (characteristics of leadership, personal learning styles, and applying reading comprehension techniques), plus pre- and post — self-efficacy scores, explained 50% of the variance.
A Low-Maintenance Approach to Improving Retention: Short On-Line Tutorials in Elementary Statistics
Authors: Sargent Carol Springer , Borthick A. Faye , Lederberg Amy R. , Haardörfer Regine
Published: April 2013

The struggle to get weak students to use learning support services plagues virtually all retention programs (Friedlander, 1980; Hodges, 2001; Karabenick & Knapp, 1988; Moore & LeDee, 2006; Simpson, Hynd, Nist, & Burrell, 1997; Webster & Dee, 1998). This study presents a cost-effective form of supplemental instruction (SI), in the form of on-line tutorials, ultra-short digital instruction suitable for high enrollment courses, designed to engage underprepared or poorly motivated students pass their required courses. Participation among the low achievers was 39.3%, improving their exam scores about a half a letter grade over non-users and students in control sections, even without giving course credit for using the SI resource. Surveys reveal what aspects of the tutorials were most effective and valued.