bluuebunny/crossref_metadata_2025 huggingface dataset:
Inventário arbóreo-urbano do município de Salto de Pirapora, SP
Authors: Benatti Daniele Porto , Tonello Kelly Cristina , Adriano Júnior Francisco Carlos , Silva José Mauro Santana da , Oliveira Ivanka Rosada de , Rolim Elce N. , Ferraz Deborah L.
Published: December 2012

Este estudo teve por objetivo realizar o inventário arbóreo-urbano em 24 bairros do Município de Salto de Pirapora, SP, por meio da avaliação quali-quantitativa. Para tanto, foram obtidas informações relacionadas à: espécie arbórea, situação da copa e do tronco, orientação do tronco, fitossanidade, interceptação das raízes no passeio, necessidade de tratos silviculturais, altura total e altura da primeira bifurcação, assim como características do espaço viário. Foram registrados 868 indivíduos, dos quais 679 foram catalogados em 71 espécies arbóreas. A espécie de maior frequência foi Caesalpinia pluviosa, representando 13,6% do total, seguida de Ficus benjamin (10,4%), Lagerstroemia indica (5,0%) e Terminalia catappa (4,8%). Quanto à condição do tronco, 68,8% dos indivíduos arbóreos não apresentaram problemas; 85,7% das árvores observadas possuíam orientação simpodial adequada; poucas árvores apresentavam danos relacionados à fitossanidade que poderiam interferir em sua integridade e, ou, longevidade; 69,6% não interferiam, de forma direta, na calçada; 32,8% das árvores necessitavam de podas por estarem acima da fiação elétrica; 0,5% necessitava de substituição; e 5,7% precisavam ser removidas. Com relação à altura total das árvores, 63,0% apresentavam crescimento menor que 5 m; e 65,3% com altura da primeira bifurcação do tronco inferior a 1,80 m. O Bairro Primavera destacou-se pelo maior número de árvores em sua urbanização. Em contrapartida, o Jardim Amélia apresentou apenas um indivíduo. Dessa forma, observou-se que cada bairro possuía sua particularidade, e ações de manutenção e enriquecimento, tanto relacionadas ao número de espécies quanto à quantidade de indivíduos, deveriam ser consideradas no planejamento urbano-arbóreo daquele município.
Toxicidade de filtrados de cultura de Alternaria euphorbiicola em folhas de Euphorbia heterophylla
Authors: Varejão E.V.V , Demuner A.J , Barbosa L.C.A , Barreto R.W , Vieira B.S
Published: December 2012

A espécie fúngica Alternaria euphorbiicola é agente causal de severas necroses de inflorescência, queimas de folhas e cancros da haste em Euphorbia heterophylla (leiteiro ou amendoim-bravo), importante planta daninha responsável por grandes prejuízos à agricultura brasileira. A aplicação de suspensões de esporos do fungo sobre populações da planta hospedeira resulta em rápida produção de necrose dos tecidos das plantas (24 a 48 horas após aplicação). Essas observações levaram à conjectura de que o fungo possa produzir fitotoxinas in vitro capazes de causar lesão às plantas. O objetivo deste trabalho foi investigar preliminarmente a produção in vitro de fitotoxinas por A. euphorbiicola sob diferentes condições de cultivo. Os resultados mostraram que a composição do meio de cultura e as condições de cultivo influenciaram a fitotoxicidade de filtrados de cultura, tendo o cultivo sob agitação e na ausência de luz favorecido a produção de metabólitos fitotóxicos pelo fungo. O filtrado da cultura em meio de Jenkins-Prior modificado, crescida sob agitação, no escuro e a 28 ºC, apresentou a maior atividade fitotóxica, tendo produzido extensas necroses foliares e desfolha em plantas de E. heterophylla. Esse filtrado de cultura foi submetido a extração seguida por fracionamento guiado por bioensaios. Uma fração cromatográfica constituída majoritariamente por ácidos graxos de cadeia longa produziu halos cloróticos e necrose de folhas, assim como observado após a inoculação de E. heterophylla com o fungo. Esses resultados sugerem a participação de ácidos graxos no processo infeccioso na associação A. euphorbiicola x E. heterophylla.
Períodos de interferência de plantas daninhas na cultura do quiabo
Authors: Bachega L.P.S , Carvalho L.B , Bianco S , Cecílio Filho A.B
Published: December 2012

Poucas pesquisas têm sido realizadas sobre interferência de plantas daninhas na cultura do quiabo. Objetivou-se com este trabalho estimar os períodos de interferência da comunidade infestante no quiabeiro. Um experimento de campo foi conduzido sob dois grupos de tratamentos, mantendo períodos crescentes de 0 (testemunha), 7, 21, 28, 35, 42, 49, 63, 77, 91 e 105 dias após a emergência da cultura (DAE), com e sem controle das plantas daninhas. As plantas daninhas com maior importância relativa foram Portulaca oleracea, Nicandra physaloides e Eleusine indica. A convivência do quiabeiro com as plantas daninhas por todo o ciclo de cultivo reduziu a produtividade da cultura em 95%. O período anterior à interferência foi de 57 DAE, enquanto o período total de prevenção à interferência foi de 14 DAE. Não houve período crítico de prevenção à interferência, sendo um único controle das plantas daninhas entre 14 e 57 DAE suficiente para prevenir a interferência na cultura do quiabo.
Emergência e crescimento inicial de cultivares de Urochloa em diferentes profundidades de semeadura
Authors: Ikeda F.S , Victoria Filho R , Vilela L , Marchi G , Cavalieri S.D , Silva A.A
Published: December 2012

Considerando a possibilidade de atrasar o crescimento inicial de gramíneas forrageiras por meio de semeaduras em maior profundidade, de forma a proporcionar vantagem competitiva à cultura de grãos em sistemas consorciados, foram avaliados a emergência e o crescimento de cultivares de Urochloa spp. em diferentes profundidades de semeadura. O experimento foi conduzido em casa de vegetação com U. brizantha cv. Marandu e cv. Piatã e U. decumbens cv. Basilisk, semeadas nas profundidades de 0, 3, 6, 9 e 12 cm. Observou-se comportamento semelhante entre os cultivares de U. brizantha quanto à porcentagem e velocidade de emergência, à altura e à massa de matéria seca de plantas aos 28 dias após a semeadura (DAS); entretanto, esses resultados diferiram dos de U. decumbens, à exceção da altura de U. brizantha cv. Piatã. As variáveis avaliadas, para todos os cultivares, tenderam à redução em profundidades maiores que 6 cm. O atraso na emergência a 0 cm, para todos os cultivares de Urochloa, não resultou em redução na altura e massa de matéria seca das plantas.
O PNPG 2011-2020: os desafios do país e o sistema nacional de pós‑graduação
Authors: Barreto Francisco César de Sá , Domingues Ivan
Published: December 2012

O artigo tem por objetivo esclarecer a comunidade acadêmica ligada à pós-graduação sobre os fundamentos e as diretrizes do PNPG 2011-2020 que acaba de ser publicado pela CAPES. Para tanto, procura-se contextualizar o novo Plano no quadro histórico mais amplo dos Planos anteriores, bem como no tempo presente e na conjuntura atual do país, com seus megadesafios, os grandes legados históricos, os problemas seculares do sistema de ensino e os caminhos para superá-los. Junto com as informações e os esclarecimentos, o leitor encontrará um conjunto de questionamentos e análises teórico-conceituais sobre os rumos da ciência e tecnologia em nosso país e seus impactos sobre o sistema de pós‑graduação, considerando as demandas, os gaps e as maneiras de processá-las e vencê-los.
Dever de casa, espelho de desigualdades educacionais e sociais
Authors: Resende Tania de Freitas
Published: December 2012

Este artigo busca analisar, a partir de resultados de uma pesquisa microssociológica, diferenças e desigualdades de diversas ordens que são espelhadas na prática social de prescrição e realização dos deveres de casa, tanto no âmbito das famílias quanto no das escolas. Em alguns casos, trata-se de desigualdades mais explícitas, como as de condições de realização dos deveres e de acompanhamento pelas famílias. Em outros, trata-se de diferenças - por exemplo, entre as práticas socializadoras familiares, ou entre práticas curriculares das escolas - que se transformam em desigualdades à medida que configuram condições desiguais para estudantes colocados, no sistema escolar e na sociedade, em situação de competição. Em todos os casos, para além dos deveres em si, o que se coloca em questão são as condições de equidade/iniquidade do sistema educacional.
Alinhamento estratégico nas cadeias de suprimento da indústria automobilística brasileira
Authors: Martins Ricardo S. , Souza Filho Osmar V. , Pereira Susana Carla Farias
Published: December 2012

O objetivo do estudo foi analisar o alinhamento nas estratégias de suprimento adotadas pelos elos nas cadeias de suprimentos da indústria automobilística no Brasil. O conceito de alinhamento seguido foi aquele proposto por Vachon et al. (2009), de que o alinhamento se relaciona com a intensidade dos gaps entre os requisitos de um cliente e a ênfase dada por um fornecedor de primeira camada nestes mesmos requisitos ao lidar com os fornecedores de segunda camada. A unidade de análise são empresas industriais localizadas no Brasil, fornecedores de primeira camada de montadoras de automóveis. A amostra de vinte e oito empresas foi selecionada por critério de acessibilidade, a partir de uma relação de empresas do setor disponibilizada pelo Sindipeças, o principal sindicato patronal da categoria. As unidades de observação foram os gestores da área de suprimentos dessas empresas. Os resultados apontam que a dependência de um fornecedor em relação a uma montadora específica reforça o alinhamento estratégico nesta cadeia de suprimentos, e que as montadoras europeias possuem uma base de fornecedores diretos que adotam estratégias de suprimentos mais alinhadas com as suas próprias, quando comparadas com as montadoras norteamericanas e respectivas bases de fornecedores. No entanto, as cadeias se desalinham quando prevalece a adoção de práticas colaborativas nas relações entre montadoras e primeira camada de fornecedores.
Uma análise dos serviços de telefonia móvel no Brasil: uma proposta de modelo empírico
Authors: Mota Márcio de Oliveira , Nogueira Cláudio André Gondim , Almeida Felipe Cavalcante de , Lima Paulo Giovanni Nogueira de , Moura Heber José de
Published: December 2012

O presente artigo busca preencher uma lacuna que os estudos efetuados anteriormente deixaram no que diz respeito à falta de informações acerca da satisfação dos consumidores dos serviços de telefonia móvel após a portabilidade numérica. No caso, realizou-se, de forma inédita, um estudo longitudinal por um período de aproximadamente três anos, com usuários de telefonia móvel antes e depois da portabilidade numérica no intuito de avaliar os serviços prestados pelas concessionárias por meio da percepção desses consumidores em períodos de distinta legislação. Há também uma segunda lacuna que se refere ao desenvolvimento de um modelo que responda e consiga atender aos atributos inerentes ao setor de telefonia móvel no que concerne à satisfação dos serviços prestados. Esse estudo tem como objetivo analisar a avaliação dos serviços de telefonia móvel brasileiro. Especificamente, pretende-se: (1) verificar empiricamente o ajustamento de um modelo de satisfação no setor de telefonia móvel baseado em modelos de satisfação do consumidor; (2) examinar a influência dos antecedentes e consequentes da satisfação de serviços de telefonia móvel; (3) analisar a avaliação dos serviços de telefonia móvel por meio de seus usuários antes e depois da portabilidade numérica; e (4) propor um índice de satisfação do consumidor para o setor de telefonia móvel brasileiro. O estudo compreendeu uma pesquisa descritiva do tipo survey.A pesquisa de campo foi realizada durante três anos junto a 1596 usuários de telefonia móvel pesquisados, sendo estes divididos entre usuários antes do início da portabilidade numérica e com usuários que realizaram a portabilidade numérica com pelo menos 12 meses após o início da autorização pela ANATEL. Os dados coletados foram submetidos a procedimentos estatísticos por meio da técnica de modelagem em equações estruturais. Os resultados apontam que não houve diferentes percepções por parte dos usuários de telefonia móvel antes e depois da portabilidade numérica, portanto, há ainda muito a se aprofundar sobre o que levou os usuários a avaliar de uma forma tão semelhante as operadoras em períodos e situações tão distintos. Verificou-se ainda que as relações entre o valor percebido e a imagem e entre a satisfação e o valor percebido se manifestaram negativamente no período antes da portabilidade numérica e que os impactos mais fortes e significativos do modelo proposto se referenciam ao relacionamento da imagem com a satisfação e da satisfação com a gestão das reclamações.
Formação de professores, educação infantil e diversidade étnico-racial: saberes e fazeres nesse processo
Authors: Dias Lucimar Rosa
Published: December 2012

Este artigo apresenta parte de pesquisa de doutorado, que teve como principal objetivo compreender os modos pelos quais professoras da primeira infância se apropriaram de conhecimentos adquiridos em cursos de formação continuada que tinham por objetivo estimular a inclusão de práticas pedagógicas que tratassem da diversidade étnico-racial. Foram analisadas duas experiências, uma desenvolvida pela Secretaria de Estado de Educação do Mato Grosso do Sul, em Campo Grande, e outra pela Secretaria Municipal de Educação de Campinas/SP. O trabalho se ancora em concepções da teoria crítica da educação, para a qual as práticas pedagógicas estão relacionadas com as práticas sociais, sendo também tarefa do professor a construção de estratégias educacionais que fomentem o respeito da diversidade étnico-racial.
Para o estilo de um gênero
Authors: Discini Norma
Published: December 2012

Procurando a experiência do encontro entre uma estilística discursiva e o pensamento de Bakhtin e do Círculo, investigaremos procedimentos que respaldam a emergência do estilo de um gênero do discurso religioso, a hagiografia. A partir do lugar teórico e metodológico oferecido pelos estudos do discurso, estaremos então subsidiados pelo pensamento bakhtiniano, em especial quanto à noção de exotopia, a qual coloca o autor como um correlato do "herói". Assim pretendemos problematizar o conceito de estilo do gênero. Estabilidades fundadas em movimentos reguladores de determinada arquitetônica genérica radicarão uma totalidade discursiva, aberta, porém, à contingência e à eventicidade do ato de enunciar.
Metallurgy of friction stir–processed Cu/B4C surface composite
Authors: Sathiskumar Ramasamy , Murugan Nadarajan , Dinaharan Issac , Vijay Santhiyagu J.
Published: December 2012

The objective of this study is to compare the microstructure and microhardness of friction stir–processed pure copper with and without B4C particulates. Friction stir processing was accomplished using a friction stir welding machine at a tool rotational speed of 1500 rpm, processing speed of 40 mm/min and axial force of 10 kN. The B4C particulates were introduced using a groove cut on the copper plate. The microstructure of the processed zone indicated fine grains and homogeneous distribution of B4C particulates in friction stir–processed copper with and without B4C particulates, respectively. The hardness of the friction stir–processed zone using B4C particulates increased and is 42% higher than that of friction stir–processed copper without B4C particulates.
Measuring and selecting scales of effect for landscape predictors in species–habitat models
Authors: Martin Amanda E. , Fahrig Lenore
Published: December 2012

Wildlife managers often use habitat models to determine species habitat requirements and to identify locations for conservation efforts, uses which depend on accurate specification of species–habitat relationships. Prior study suggests that model performance may be influenced by the way we measure environmental predictors. We hypothesized that species responses to landscape predictors are best represented by landscape composition‐based measurements, rather than distance‐based measurements. We also hypothesized that models using empirical data to select an appropriate scale of effect for each habitat predictor (multi‐scale models) should perform better than models that assume a common scale of effect for all predictors (single‐scale models). To test these hypotheses we constructed habitat models for three mammal species, Mephitis mephitis, Mustela erminea, and Procyon lotor, based on surveys conducted in 80 landscapes in southeastern Ontario, Canada. For each species we compared the performance of distance‐ and composition‐based measurements, and we compared the performance of single‐ and multi‐scale models. The composition‐based measurement, measured at its empirically determined scale of effect, had greater explanatory power than the distance‐based measurement of a given predictor more often than expected by chance, supporting our first hypothesis. Contrary to expectation, multi‐scale models did not have better explanatory power or predictive performance relative to single‐scale models. We identified and evaluated four potential mechanisms to explain this, and, depending on the species, we found that the best explanation was either that predictors have significant effects at a common scale or that, although the modeled effects were at multiple scales, they were of similar magnitude and direction at the scales modeled in single‐ and multi‐scale models. Our results suggest that habitat modeling based on distance‐based measurements could be improved by including composition‐based measurements of landscape predictor variables, but that inclusion of predictor‐specific scales of effect for composition‐based measurements does not necessarily improve performance over models including composition‐based measurements at a single scale. Conservation and wildlife management may be simplified when single‐scale models perform as well as multi‐scale models, as this suggests actions conducted at a single scale may address management objectives as well as actions taken at different scales for different landscape features.
A semiparametric Bayesian method for detecting Allee effects
Authors: Sugeno Masatoshi , Munch Stephan B
Published: December 2012

The importance of Allee effects has long been recognized both in theoretical studies of population dynamics and in conservation sciences. Although the necessary conditions for Allee effects to occur (e.g., difficulty in finding mates and mortality driven by generalist predators at low density) would seem to apply to many species, evidence for Allee effects in natural populations is equivocal at best. This apparent scarcity might be an artifact driven by poor power to detect them with traditional parametric models. To circumvent this potential problem, we developed a semiparametric Bayesian method based on a Gaussian process prior. We validated the method using simulated data sets and applied it to three herring data sets.
Modeling Gel Filter Cake Recovery by Flow and Dilution Mechanisms
Authors: Gdanski Rick , Bryant Jason
Published: December 2012

Historical modeling of gel filter cake recovery often predicts relatively fast gel recovery. A common method to slow gel recovery in simulations is to use yield point behavior for the gel filter cake. Recent measurements of concentrated, broken gel exhibited Carreau-type viscosity behavior that could mimic an apparent yield point. A new rheology model built on those measurements was used to upgrade a fracture cleanup and chemistry simulator (FCCS) to study potential cleanup mechanisms of gel filter cake during flowback of fracturing treatments.

Two cleanup mechanisms were explored with the FCCS. The first was a simple dilution mechanism in which the gel filter cake was immediately diluted as water re-entered the proppant pack from the matrix. The method used two-phase flow modeling and predicted excellent cleanup of delinked borate filter cakes and high concentrations of gelling agents in the return fluids—a prediction not observed in well returns. The second mechanism required development of three-phase relative permeability curves for water, gel filter cake, and gas phases in the proppant pack. The simulation studies using this mechanism only modeled displacement cleanup and predicted poor recovery as a result of a combination of filter cake rheology and relative permeability. This affirmed the poor apparent cleanup of some fracturing treatments, but underestimated return gelling agent concentration. The studies also demonstrated the role of gel phase saturation on gas productivity.

This work demonstrates that a proper choice of the operative three-phase relative permeability curves for water, gel filter cake, and gas is important for constraining the premature return of gel filter cake in cleanup simulators. Future laboratory work should consider the direct measurement of the three-phase relative permeability curves in proppant packs.
Predicting Well Performance in Complex Fracture Systems by Slab Source Method
Authors: Lin Jiajing , Zhu Ding
Published: December 2012

Multiple hydraulic fracture treatments in reservoirs with natural fractures create complex fracture networks. Predicting well performance in such a complex fracture network system is an extreme challenge. The statistical nature of natural fracture networks changes the flow characteristics from that of a single linear fracture. Simply using single linear fracture models for individual fractures, and then summing the flow from each fracture as the total flow rate for the network could introduce significant error. In this paper we present a semi-analytical model by a source method to estimate well performance in a complex fracture network system. The method simulates complex fracture systems in a more reasonable approach. We statistically assigned a fracture network of natural fractures, based on the spacing between fractures and fracture geometry. We then added multiple dominating hydraulic fractures to the natural fracture system. Each of the hydraulic fractures is connected to the horizontal wellbore, and some of the natural fractures are connected to the hydraulic fractures through the network description. Each fracture, natural or hydraulically induced, is treated as a series of slab sources. The analytical solution of superposed slab sources provides the base of the approach, and the overall flow from each fracture and the effect between the fractures are modeled by applying the superposition principle to all of the fractures. The fluid inside the natural fractures flows into the hydraulic fractures, and the fluid of the hydraulic fracture from both the reservoir and the natural fractures flows to the wellbore. The finite conductivity of hydraulic fractures is modeled by additional pressure drop inside the fracture, but it is neglected in natural fractures. This paper also shows that non-Darcy flow effects have an impact on the performance of fractured horizontal wells. In hydraulic fracture calculation, non-Darcy flow can be treated as the reduction of permeability in the fracture to a considerably smaller effective permeability. The reduction is about 2% to 20%, due to non- Darcy flow that can result in a low rate.

The semi-analytical solution presented can be used to efficiently calculate the flow rate of multistage-fractured wells. Examples are used to illustrate the application of the model to evaluate well performance in reservoirs that contain complex fracture networks.
Investigation of Horizontal Well Fracture Extension Pattern Based on Downhole Pressure Data
Authors: Daneshy Ali , Herman Daniel , Tymko Dean
Published: December 2012

This paper presents the results of an investigation into fracture growth pattern in three horizontal wells, each fractured multiple times. The completion system was selected such that it allowed recording of the bottom-hole pressure in two critical locations; at the frac port which was being fractured, and, within the previously fractured part of the same wellbore. Downhole cups isolated the two locations from each other.

The data show remarkable results. All fractures initiated axially and re-oriented to become perpendicular to the minimum principal stress (MPS). The re-orientation details varied widely between different fractures in the same well, and also between wells. In-spite of these variations, there was no communication within the formation between the multiple fractures. All fractures in the same well had the same value of MPS, and in fact nearly the same in all three wells. In one of the wells there was obstruction to proppant movement inside the fracture which caused increasing pressures during fracture extension. In one instance this resulted in screen-out very near the wellbore early in the treatment, and in another case inside the fracture and close to the end of the stage. Still, the high pressures encountered during these fractures did not cause communication with the previous fractures. The growth pattern in all fractures can best be described as off-balance, with no evidence of "complexity".
Resource Evaluation for Shale Gas Reservoirs
Authors: Dong Z. , Holditch S. A. , McVay D. A.
Published: December 2012

Many shale gas reservoirs have been previously thought of as source rocks, but the industry now finds these source rocks still contain large volumes of natural gas and liquids that can be produced using horizontal drilling and hydraulic fracturing. However, one of the most uncertain aspects of shale gas development is our ability to accurately forecast gas resources and shale gas development economics. The uncertainty of the problem begs for a probabilistic solution.

The objective of our work was to develop the data sets, methodology and tools to determine values of original gas in place (OGIP), technically recoverable resources (TRR), recovery factor (RF) and economic viability in highly uncertain and risky shale gas reservoirs. Existing approaches for determining values of TRR, such as the use of decline curves or even volumetric analyses, may not be reliableduring early time because there may not be enough production history for decline curves to work well or the uncertainty in the reservoir properties may be too large for volumetric analyses to be useful.

To achieve our research objective, we developed a computer program, Unconventional Gas Resource Assessment System (UGRAS). In the program, we integrated Monte Carlo technique with an analytical reservoir simulator to estimate the original volume in place, predict production performance and estimate the fraction of TRR that are economically recoverable resources (ERR) for a variety of economic situations. We applied UGRAS to dry gas wells in the Barnett Shale and the Eagle Ford shale to determine the probabilistic distribution of their resource potential and economic viability. Based on our assumptions, the Eagle Ford shale in the dry gas portion of the play has more technically recoverable resources than the Barnett shale. However, the Eagle Ford shale is currently not as profitable as the Barnett shale because of the higher drilling costs in the Eagle Ford dry gas window.

We anticipate that the tools and methodologies developed in this work will be applicable to any shale gas reservoirs that have sufficient data available. These tools should ultimately be able to allow determination of technically and economically recoverable resources from shale gas reservoirs globally.
Acid Fracturing: New Insigths on Acid Etching Patterns from Experimental Investigation
Authors: Neumann L F , de Oliveira e Sousa J L , Brandão E M , Oliveira T J
Published: December 2012

Nowadays, it is commonplace to say that acid fracture conductivity depends on the fracture face asperities. Does it really depend on it? Almost thirty years ago, someone wrote, "We believe the conductivity measured in these tests is mainly due to the smoothing of peaks and valleys on the rough fracture faces, and is independent of rock heterogeneities due to the small sample size." Moreover, almost one year ago, one wrote, "More asperities touch and deform as the closure stress increases. The channels become even shorter and fewer openings are left." Between these two extremes, the asperities came to be pointed out as an essential factor to generate acid conductivity. Many published results from small, wet sawed and leveled carbonate rock samples support such claim. We did the same. Our experimental investigation on small scale carbonate samples with sawn faces, both from outcrops and well cores, reconfirm the existence of three main acid patterns namely uniform, channels and roughness. The design of experimental apparatus prevented that those etching patterns were artifact patterns. The acid etching patterns determine different conductivity behavior under confining stress. However, hydraulic fractures are tensile fractures and they are naturally rough. In nature, there is no such thing as a leveled fracture face. Tensile fracture faces could be rougher than fracture face after acid reaction. In fact, the first experimental results show that after acid reaction, linear roughness of tensile fractures can be larger, equal or less than linear roughness before acid reaction. This paper presents experimental results and discusses the asperities paradigm.
Gas Shale Hydraulic Fracturing: A Numerical Evaluation of the Effect of Geomechanical Parameters
Authors: Nagel Neal B. , Sanchez-Nagel Marisela , Lee Byungtark
Published: December 2012

Due to the low permeability of many shale gas reservoirs, multi-stage horizontal well completions are used to provide sufficient stimulated area to make an economic well. Furthermore, access to, and stimulation of, the natural fracture system is often critical to an economically successful well.

During a given hydraulic fracture stimulation, the physical displacement of the fracture alters the stress field around it. Numerous authors have suggested that this altered stress field is beneficial to the stimulation of the natural fracture system; however, other authors have shown the potential to stabilize the natural fracture system - making it less likely to shear - due to the presence of a created hydraulic fracture.

In this paper, we present the results of a detailed parametric evaluation of the shear failure (and, by analogy, the microseismicity) due to the creation of a hydraulic fracture as a function of fracture length within two different fracture networks (DFNs) using the 2D Distinct Element Model (DEM), UDEC. Simulations were conducted as a function of: 1) fracture strength; 2) DFN orientation within the stress field; 3) stress ratio (the ratio of the maximum horizontal stress to the minimum); 4) Poisson’s ratio of the shale; and 5) Young’s modulus of the shale. The results show the critical impact that changes in the hydraulic fracture length and the DFN orientation have on the shear of the natural fracture system. In contrast, the simulations suggest that stress ratio, Poisson’s ratio, and Young’s modulus have, at best, a second-order effect on the shearing - and likely the stimulation - of the natural fracture system.

The results of the study provide a further, quantitative assessment of the critical parameters affecting shale gas completions and aid in the understanding and optimization of hydraulic fracture stimulations in very low permeability, naturally fractured reservoirs.
Prediction And Optimization Of Fracturing In Tight Gas And Shale Using A Coupled Geomechanical Model Of Combined Tensile And Shear Fracturing
Authors: Nassir Mohammad , Settari Antonin , Wan Richard
Published: December 2012

Hydraulic fracturing is a stimulation technique essential for economical development of tight gas and shale gas reservoirs. Analysis of the performance of fracturing jobs and optimization of the treatment design requires modeling which accounts for all important features of the process and ideally covers both the treatment and post-stimulation production of the well. It is now well established that the productivity of the wells is due not only to the classical tensile single plane fracture (SPF), but to the development of an enhanced permeability region (stimulated reservoir volume or SRV) around it due to shear fracturing and/or stimulation of existing dual porosity. The shape and size of the SRV depends not only on the injection process but also on the geomechanics of the reservoir. Current techniques are not able to predict its dependence on frac job parameters, which precludes any meaningful optimization. Typically the SRV size is assumed (e.g., from microseismic) in production forecasting.

In this work we have developed a new coupled geomechanical and flow model for analysis and optimization of tight and shale gas treatments. The formulation includes the propagation of a tensile (SPF) fracture and dynamic development of the shear failure. Non-fractured blocks are assumed to be of linear elastic material; whereas in the failed blocks, fractures and rock compliance matrices are homogenized to form an equivalent compliance matrix. Simple Mohr-Coulomb and tensile failure relationships were used as the criteria for detecting fracture creation. Hyperbolic functions are used to describe the fracture normal and pre-peak shear deformations while the post-peak shear behavior follows an elasto-plastic model. The permeability enhancement during the fracturing process is computed and is the principal coupling between the flow and geomechanics. The model is 3-dimensional and treats both normal and shear behaviour of fractures. The simulation results reveal that shear fracturing will be the dominant fracturing mechanism in cases where the rock cohesion is low and the deviatoric stress is high, whereas tensile fracturing prevails in other conditions.

The new model will be a realistic tool for analyzing the dependence of the well productivity on design parameters such as stage volume and pumping rate, spacing between stages, etc. It can be also used to screen shale plays for the most favorable geomechanical conditions.
Integrated Methodology for Optimizing Development of Unconventional Gas Resources
Authors: Gupta Jugal K. , Zielonka Matias G. , Albert Richard A. , El-Rabaa Wadood , Burnham Heather A. , Choi Nancy H.
Published: December 2012

Fracture nucleation and propagation are controlled by in-situ stresses, fracture treatment design, presence of existing fractures (natural or induced), and geological history. In addition, production driven depletion and offset completions may alter stresses and hence fracture growth. For unconventional oil and gas assets the complexity resulting from the interplay of fracture characteristics, pressure depletion, and stress distribution on well performance remains one of the foremost hurdles in their optimal development, impacting infill well and refracturing programs.

To this end, ExxonMobil has undertaken a multi-disciplinary approach that integrates fracture characteristics, reservoir production, and evolution of the stress field to design and optimize developments of unconventional assets. In this approach, fracture modeling and advanced rate transient techniques are employed to constrain fracture geometry and depletion characteristics of existing wells. This knowledge is used in finite element geomechanical modeling (coupling stresses and fluid flow) to predict fracture orientation in nearby wells.

In this paper, an integrated methodology is described using case studies for two shale gas pads. The study reveals a strong connection between reservoir depletion behavior and the spatial and temporal distribution of stresses. These models predict that principal stresses are influenced far beyond the drainage area of a horizontal well and hence play a critical role in fracture orientation and performance of neighboring wells. Strategies for manipulating stresses were evaluated to control fracture propagation by injecting, shutting-in, and producing offset wells. Collective interpretation of completion, reservoir depletion and changes in stresses explained varying performances of wells and enabled evaluation of infill potential on the pad. This workflow can be used to develop strategies for (1) optimal infill design, (2) controlling propagation of fractures in new neighboring wells, and (3) refracturing of existing wells.
Assessing the Spacing of Stages in Plug-and-Perf Completions Through Seismic Moment Tensor Inversion
Authors: Baig Adam , Urbancic Ted , Mace Kaitlyn , Prince Marc
Published: December 2012

Hydraulic fracture completions seek to balance spacing of treatment wells and perforation clusters in order to minimize the costs of drilling wells and pumping fluids and proppant downhole while promoting the development of a discrete fracture network to connect even the most isolated pockets of hydrocarbon. To this end, numerous strategies for well completions have been proposed, such as avoiding the overlap of treatment volumes between adjacent wells and/or stages because of the risk that proppant and fluid will preferentially be diverted into earlier treated volumes. In counterpoint, it has also been suggested that the creation of new fractures in a previously treated volume promotes a complex fracture network enhancing drainage. When these stimulations are monitored from multiple arrays surrounding the treatment zone, seismic moment tensor inversion (SMTI) offers the ability to test these hypotheses by inferring if the events represent the opening of fractures or closure of pre-existing natural or newly created fractures. In this paper, we discuss two different completion programs. One common thread between the two data sets is that observed event clusters occur with a significant degree of overlap between neighbouring stages. Both completions were monitored with optimal multi-array configurations allowing for the calculation of SMTI with a high degree of robustness. The first stages in both examples showed significant opening components of failure. Neighbouring subsequent stages show closure events in the overlapping regions suggesting that the previously opened fractures were now closing due to local re-orientations of the stress-strain field stress induced by the later injection over-printing the region of overlap. Based on these analyses, it can be suggested that the moment tensor response can be used to identify the effective spacing for perforation clusters and establish optimal stimulation programs, which could include setting fracture ports farther apart.
Assessing Stimulation of Complex Natural Fractures as Characterized Using Microseismicity: An Argument the Inclusion of Sub-Horizontal Fractures in Reservoir Models
Authors: Urbancic Ted , Baig Adam , Goldstein Shoshana
Published: December 2012

The inclusion of fracture networks in reservoir models is generally based on the concept of failure associated with sub-vertical fractures. In general, it is surmized that fractures can grow irregularly in a stress field that is perturbed by a hydraulic fracture injection. It has also been considered that structural weaknesses in the rock such as pre-existing fractures and naturally occurring laminations commonly found in shale-gas reservoirs can be conduits for fracturing during stimulation and active pathways for fluid flow. We postulate that local stress perturbations through stress transfer allows for fractures to propagate and initiate failure along pre-existing fracture sets, which include sub-vertical and sub-horizontal fractures. Additionally, the degree of fracture interconnectivity and the type of fracturing will play a role in whether effective proppant transport is achieved. Through moment tensor inversion of microseismic events related to stimulation in the Horn River Basin utilizing well-conditioned geophone arrays, we have been able to define a three dimensional discrete fracture network consisting of sub-horizontal and sub-vertical fractures. Geologic data from the site provided corroborative evidence to the validity of the observed discrete fracture network, the presence of sub-horizontal fractures and fracture orientations in-line with current regional stress field. The fracture intensity and complexity appeared to be directly related to the degree of interaction between the sub-horizontal and sub-vertical fractures. Regions dominated by sub-horizontal fractures were also regions exhibiting poor fracture intensity and complexity. Based on these observations and moment tensor derived failure modes (opening component of failure), we were able to identify regions of enhanced fluid flow, further identifying regions of effective fluid transport. Regions with poor connectivity and dominance of sub-horizontal fractures also were identified as regions of poor fluid flow; these then become regions for potential re-stimulation. Based on these analyses, it can be suggested that sub-horizontal fractures can play an important role in the overall fracture development.
Phosphonic/Hydroflouric Acid – A Promising New Weapon in the Tortuosity Remediation Arsenal for Fracturing Treatments
Authors: Melo Ricardo , Curtis James , Gomez Julio , Melo Alexandre , Garcia Fernando , Pedrosa Helio
Published: December 2012

Tortuosity has been one of the biggest challenges for shale and tight gas hydraulic fracturing treatments, leading to high near-wellbore friction pressures, premature screen-outs, reduced treating rates and poor production results. Several solutions have been applied with varying levels of success, but often result in nothing more than a frustrating attempt.

A new solution has been developed that has demonstrated substantial success in overcoming particularly stubborn tortuosity problems. The method builds upon the use of a non-damaging, single-stage phosphonic/hydrofluoric acid system (SAS) that has been well established around the globe for matrix stimulation treatments in a single stage (without an acid pre-flush). These encouraging results in matrix treatments encouraged us to consider the SAS for hydraulic fracturing applications.

An opportunity arose in a tight gas fracturing campaign in Northeast Brazil, where severe tortuosity prevented us from achieving the required pump rate while staying below the surface treating pressure limitation. Conventional tortuosity-mitigation methods such as proppant slugs, viscous fluids, re-perforating and sand-jetting all failed to solve the problem. The novel technique was tested (to the authors’ knowledge for the first time anywhere), whereby a high-strength SAS was injected at fracturing rates and pressures, without any pre-flush, in order to clean up the tortuosity and improve injectivity. The tight gas well was subsequently hydraulically fractured in six perforated intervals, with a SAS pre-frac performed prior to each stage. Injection rates in the main fracturing treatments were improved by 25 to 100 percent.

This paper describes the SAS technique, including acid properties, treatment design overview, field results and measured tortuosity improvements.
Alterations in Molecular Composition of Humic Substances from Eucalypt Plantation Soils Assessed by 13C‐NMR Spectroscopy
Authors: Barros Soares Emanuelle Mercês , Silva Ivo Ribeiro , de Novais Roberto Ferreira , Hu Yan-Yan , Schmidt-Rohr Klaus
Published: December 2012

Land‐use changes with natural vegetation removal may impact the quantity and quality of humic substances (HS), including their molecular nature. Nuclear magnetic resonance (NMR) experiments were used in the present study to evaluate the alterations in the molecular composition of fulvic (FA) and humic (HA) acids from soils under eucalypt plantations in three major biomes in Brazil: Atlantic Forest, Cerrado, and Grassland. The major NMR‐identifiable components in these HS were aromatics including aromatic C‐O, COO/NC = O groups, peptides, carbohydrates, lignin‐derived moieties and nonpolar alkyls. In all biomes the dipolar dephasing technique indicated the presence of significant amounts of condensed aromatic C, possibly inherited from charred materials derived from natural and anthropogenic fires in the region. The nonpolar alkyl C to O‐alkyl C ratio averaged 1.4 for HA and 1.1 for FA. Humic substances from eucalypt soils showed greater contribution of nonpolar alkyl groups and a smaller abundance of O‐alkyl groups in comparison to the native vegetation soil. Sugarcane (Saccharum officinarum L.) cultivation increased HA aromatics in comparison to those from the native Atlantic Forest soil, but when sugarcane was substituted by eucalypt the aromatics decreased and O‐alkyl C recovered in HA and FA. There was evidence of greater contribution of lignin‐derived C for HA and FA in sites planted with Brachiaria spp. pastures. Except for the HA from one Cerrado soil (Itacambira), aromaticity of HA decreased following planting to eucalypt. These changes in HS molecular composition across biomes may have impact on soil organic matter processes and they should be taken into account in future studies.
The Quality of Life of Hematological Malignancy Patients with Major Depressive Disorder or Subsyndromal Depression
Authors: Rezaei Omid , Sharifian Ramezan-Ali , Soleimani Mehdi , Jahanian Amirabbas
Published: December 2012

Objective:

The purpose of the present study was to compare the quality of life of hematological malignancy patients with major depressive disorder or subsyndromal depression.

Method:

Sample consisted of 93 hematological malignancy patients recruited from oncology ward of Valieasr hospital for Imam Khomeini complex hospital at Tehran through purposeful sampling. Participants were divided into three groups through diagnostic interview based on DSM-IV-TR criteria and the Beck Depression Inventory-2 (BDI-II): Major depressive disorder (MDD) ( n = 41; 44.1%); subsyndromal depression (SSD) ( n = 23; 24.7%), and without depression (WD) ( n = 29; 31.2%). Participants completed the short-form health survey (SF-36) as a measure of the quality of life. We carried out an analysis of covariance to examine the collected data.

Results:

Findings showed that there was not a significant difference between patients with MDD and SSD based on measure of quality of life. But patients with MDD and SSD showed significantly worse quality of life than patients with WD. This finding highlights the clinical importance of subsyndromal depressive symptoms and casts doubt on the clinical utility of separation between MDD and subsyndromal depression in terms of important clinical outcomes.
Functionalization of thermo-acid activated sepiolite by amine-silane and mercapto-silane for chromium(VI) adsorption from aqueous solutions
Authors: Marjanovic Vesna , Lazarevic Slavica , Jankovic-Castvan Ivona , Jokic Bojan , Bjelajac Andjelika , Janackovic Djordje , Petrovic Rada
Published: December 2012

Chromium(VI) adsorption from aqueous solutions onto thermo-acid activated
sepiolite functionalized with (3-mercaptopropyl)trimethoxy-silane and
[3-(2-aminoethylamino)pro-pyl]trimethoxy-silane, was investigated. Scanning
electron microscopy, X-ray diffraction, Fourier transform infrared
spectroscopy, thermogravimetric and differential thermal analysis, nitrogen
adsorption-desorption, and determination of the point of zero charge were
used to characterize the obtained adsorbents. It has been established that
the silanes were successfully grafted on the thermo-acid activated sepiolite
surfaces and that the structure of parent material was preserved during the
functionalization. The adsorption of Cr(VI) onto functionalized thermo-acid
activated sepiolite was tested as a function of initial pH values at 298 K.
The amine functionalized thermo-acid activated sepiolite showed a higher
adsorption capacity than the mercapto functionalized thermo-acid activated
sepiolite at all studied initial pH values, especially at the initial pH = 2.