bluuebunny/crossref_metadata_2025 huggingface dataset:
Mortalidade materna e sua interface com a raça em Mato Grosso
Authors: Teixeira Neuma Zamariano Fanaia , Pereira Wilza Rocha , Barbosa Dulce Aparecida , Vianna Lucila Amaral Carneiro
Published: June 2012

OBJETIVOS: analisar a correlação entre óbitos maternos e raça/cor no Estado de Mato Grosso entre os anos de 2000 a 2006. MÉTODOS: estudo epidemiológico com base nos dados da Declaração de Óbitos, DATASUS e SIM/SES-MT, que propiciaram a análise da série histórica entre esses anos. Relacionou-se raça/cor das mulheres que foram a óbito por causas maternas com as variáveis idade, escolaridade, estado civil, causa básica de óbito e tipo de causa obstétrica. Utilizaram-se teste de Χ2 e odds ratio. RESULTADOS: o teste Χ2 evidenciou associação significativa entre raça/cor e morte materna, ao nível de significância de 95%. A odds ratio apontou uma razão de chances dessas mortes 5,13 vezes maior para mulheres pretas e 5,71 para indígenas, comparadas às mulheres brancas. "Transtornos hipertensivos da gravidez, parto/puerpério" foram a principal causa de óbito materno para as afrodescendentes e pardas; respectivamente 45,4% e 29,93%. As indígenas morreram mais pelas "complicações do trabalho de parto/parto" com 27,2%. Das mulheres brancas, 30,7% morreram por "outras complicações obstétricas não classificadas em outras causas". CONCLUSÕES: em todo Mato Grosso as mortes maternas por causas obstétricas diretas pervaleceu entre mulheres pretas e indígenas.
Gender and sexual violence among students at a brazilian university
Authors: Zotareli Vilma , Faúndes Anibal , Osis Maria José Duarte , Duarte Graciana Alves , Sousa Maria Helena de
Published: June 2012

OBJECTIVES: the prevalence of gender and sexual violence, its association with gender and ethical attitudes and the experience of suffering and perpetration of violence were evaluated among students at a public university in Brazil. METHODS: a cross-sectional study analyzed the answers given by 2430 students to a questionnaire sent by internet. RESULTS: among girls, 56.3% had been subjected to some kind of violence and 9.4% to sexual violence since university admission; 29.9% of men reported having perpetrated some kind of violence, 11.4% gender and 3.3% sexual violence. Multivariate analysis showed that living with parents/relatives was a protective factor for women being subjected to and men perpetrating sexual violence but not for "any type of violence". Lower scores for ethical attitudes were associated with a greater likelihood of men perpetrating any kind of or gender violence. Student for whom religion was important had a lower risk of being a perpetrator of any type and of sexual violence, but not gender violence. CONCLUSIONS: the findings may be useful for the discussion of this problem and to propose interventions to prevent or minimize the problems of gender and sexual violence on campus. Further studies in other university contexts need to be carried out to increase knowledge and explore possibilities for intervention.
Factores psicosociales asociados a un alto, medio y bajo riesgo de síntomas depresivos en el posparto inmediato
Authors: Paolini Cynthia Inés , Oiberman Alicia Juana , Balzano Silvia
Published: June 2012

OBJETIVOS: evaluar factores psicosociales asociados a síntomas depresivos en el posparto inmediato. MÉTODOS: 45 mujeres puérperas de un hospital público de Buenos Aires, Argentina, fueron entrevistadas entre el 1er y el 3er día posparto, de marzo-diciembre 2010. La Escala de Depresión Posnatal de Edimburgo (EPDS) fue administrada para evaluar síntomas depresivos. La entrevista psicológica perinatal (EPP) fue administrada para detectar variables psicosociales. A partir de los resultados obtenidos en la EPDS, se separó la muestra en tres grupos con diferentes grados de riesgo de sintomatología depresiva: "negativas o de bajo riesgo", "positivas de riesgo medio" y "positivas de alto riesgo". Los puntajes de corte utilizados fueron 9 y 19. RESULTADOS: se encontraron diferencias significativas entre los tres grupos con violencia familiar, migración, historia previa de depresión, presencia de síntomas depresivos durante el embarazo y mayor cantidad de estresores. CONCLUSIONES: el establecimiento de los dos puntajes de corte en la EPDS permite una detección temprana de las mujeres que presentan síntomas depresivos. Se sugiere la utilidad del puntaje de corte de 19 para la detección temprana de mujeres con mayor riesgo de desarrollar depresión posparto.
Temporal lobe epilepsy with unilateral hippocampal sclerosis and contralateral temporal scalp seizure onset: report of four patients with "burned-out hippocampus"
Authors: Caboclo Luís Otávio Sales Ferreira , Garzon Eliana , Miyashira Flávia Saori , Carrete Jr Henrique , Centeno Ricardo da Silva , Yacubian Elza Márcia Targas , Sakamoto Americo Ceiki
Published: June 2012

ABSTRACT OBJECTIVES: Patients with temporal lobe epilepsy (TLE) and unilateral severe hippocampal sclerosis (HS) may have contralateral temporal scalp ictal onset. This has recently been called "burned-out hippocampus", which is believed to be a rare entity. In this study we report four patients with unilateral hippocampal sclerosis and contralateral ictal onset registered by scalp electrodes. We discuss the importance of such cases in presurgical evaluation of patients with TLE, as well as possible strategies used for evaluation of these particular cases. PATIENTS AND METHODS: We reviewed charts from all patients with TLE submitted to pre-surgical evaluation, which included high resolution MRI and prolonged video-electroencephalogram (video-EEG) monitoring with scalp and sphenoidal electrodes, during a three-year period (2002-2004). We looked for patients who only had seizures that were clearly contralateral in location to the atrophic hippocampus. RESULTS: Four patients fulfilled the criteria above. Two of these patients had semi-invasive video-EEG monitoring with foramen ovale (FO) electrodes, which revealed seizures originating from the temporal lobe with the atrophic hippocampus, hence confirming false lateralization in the scalp-sphenoidal EEG. These patients were submitted to surgical treatment and had favorable prognosis after surgery. CONCLUSIONS: Burned-out hippocampus syndrome may not be as rare as it was previously believed. Further studies will be necessary before one can affirm that patients with unilateral HS and scalp ictal EEG showing contralateral ictal onset may be operated without confirmation of the epileptogenic zone by invasive monitoring. In these patients, semi-invasive monitoring with FO electrodes might be an interesting alternative.
Epilepsy and marijuana - a review
Authors: Dantas Fábio Galvão
Published: June 2012

ABSTRACT The medicinal use of components of Cannabis sativa (marijuana) has been studied around the world. Some of these components may have anti-convulsive properties, though the reports are controversial, and sometimes come from single case reports and clinical anecdotes. Because of ethical aspects, as some of the components of cannabis have psychotropic effects, this is a very important issue. New researches have demonstrated that some components of cannabis that don't have psychotropic action may play a role in controlling seizures. This paper reviews the relation between epilepsy and the components of cannabis sativa.
Dynamic assessment of high-resolution MRI with multi-planar reconstruction increases the yield of lesion detection in patients with partial epilepsy
Authors: Santos Sérgio L. M. , Ghizoni Enrico , Li Li M. , Cendes Fernando
Published: June 2012

Objective: To investigate the presence and type of lesions associated with partial epilepsies by routine high resolution MRI and multi-planar reconstruction (MPR) and correlate the MRI abnormalities with semiology and EEG findings. Methods: We studied 100 consecutive patients followed in the epilepsy clinic of our Hospital with partial epilepsy who underwent MRI investigation. The MRI protocol included 6 mm sagittal T1-weighted, 3-4 mm axial T1 and T2-weighted, 3 mm coronal T1 inversion recovery and T2-weighted images that were printed on a radiographic film for routine analysis. In addition, all patients had a volume T1-gradient echo acquisition with isotropic voxels (1-1.5 mm) for multiplanar reconstruction (MPR). The MRIs were examined in two different occasions: first using only the images printed on films, without volume T1-gradiente echo acquisition and in a second occasion in a computer workstation when all the available images and MPR were analyzed blindly to the clinical information. The clinical and EEG findings were tabulated independently, and results were compared using Chi-square of Fisher exact test when appropriate. Results: The patients were divided into 10 groups according to their etiological classification (structural lesions) established by MRI. Mesial temporal sclerosis (MTS) was the largest group (40%). There were 65 women and 35 men. Mean age was 23.9 (± 5.7) years and mean age of onset of recurrent seizures was 9.9 (± 0.8) years. The most frequent risk factors were family history of seizures (23%), head trauma (10%),peri-natal anoxia (5%) and infection (9%). High resolution MRI including thin coronal slices, in addition to a “dynamic” analysis in a workstation with MPR, allowed a significant improvement in lesion detection compared to the traditional analysis with radiographic films (94% versus 80%) (p < 0.05). The lesions previously undetected were focal cortical dysplasia and subtle MTS. There was a good concordance between MRI lesions and clinical and EEG findings. Conclusion: High resolution MRI including thin coronal slices, in addition to a “dynamic” analysis in a workstation with MPR allowed a significative improvement in lesion detection compared to the traditional analysis with radiographic films (94% versus 80%). Patients with partial epilepsy and “normal” MRI need to be investigated further with thin slices and post-processing techniques using volume acquisitions that allow adequate multiplanar re-slicing.
Geradores do P50: estudo com pacientes epilépticos, submetidos à amígdala-hipocampectomia
Authors: Becker Jefferson , Gomes Irenio , Silva Filho Hélio Fernandes da , Schuch Alice , Ramos Fernanda Lia de Paula , Ghisolfi Eduardo S. , Ehlers João Arthur C. , Nora Daniel Bocchese , Lara Diogo R. , Costa Jaderson Costa da
Published: June 2012

Objetivos: Estudar o envolvimento do hipocampo na gênese do potencial evocado P50 e da supressão do mesmo em pacientes com epilepsia submetidos a tratamento cirúrgico. Metodologia: Foi realizado um estudo transversal com grupo controle de comparação Excluíram-se indivíduos com outra patologia neurológica ou psiquiátrica, hipoacusia auditiva, história familiar de transtornos psicóticos, uso de antipsicóticos atípicos ou de drogas ilícitas no último mês. Os indivíduos foram separados em dois grupos: grupo 1 (n = 34) - amígdala-hipocampectomia; grupo 2 (n = 40) - controles. Foi realizado, em todos os participantes, o potencial evocado auditivo de média latência P50. Consideraram-se variáveis de comparação: as amplitudes individuais dos potenciais evocados pelo primeiro (S1) e segundo (S2) estímulos e o parâmetro de supressão do P50 (razão S2/S1). Para comparar as médias entre os grupos, foi utilizado o teste t de Student e, para comparação da freqüência de supressão, foi utilizado o teste do qui-quadrado. Resultados: A média da razão S2/S1 foi de 0,74 ± 0,44 no grupo 1 e de 0,42 ± 0,24 no grupo 2 (p < 0,001). A comparação das amplitudes médias das ondas entre os grupos mostrou uma diferença apenas na amplitude de S2, menor no grupo 2 (p < 0,001). Conclusões: Nessa pesquisa, observou-se que provavelmente o hipocampo não seja o gerador das ondas P50 nos potenciais auditivos, embora possivelmente esteja envolvido na sua supressão.
Memory tests are not good predictors of surgical outcome in patients with mesial temporal Lobe epilepsy associated with hippocampal sclerosis
Authors: Escorsi-Rosset Sara , Bianchin M Marino. , Walz Roger , Terra-Bustamante Vera C. , Carlotti Jr. Carlos G. , Assirati Jr. João A. , Santos Antonio C. , Sakamoto Américo C.
Published: June 2012

Introduction: One of the objectives of pre-surgical evaluation in mesial temporal epilepsy associated to hippoocampal sclerosis is the identification of patients with bad surgical prognosis for seizure control. At least theoretically, neuropsychological tests could be used in this venue. Objective: To evaluate whether verbal and visual memory tests can be used as isolate predictors of the post-surgical seizure outcome in patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis refractory to pharmacological treatment. Methods: In a retrospective cohort study using the control of epileptic seizures as end-point, we evaluated 187 patients and calculated the correlation of clinical variables, cognitive evaluation, neuroimaging data, demographic data and electrophysiological findings with the result of seizure control after lobectomy in these patients. Results: An unfavorable prognosis during the postoperative period was observed only in association with low visual reproduction scores (visual memory). However, after Bonferroni correction, which was necessary to reduce the chance of type I error, this result was found to be spurious. Conclusion: We conclude that neuropsychological tests of verbal and visual memory such as those used in the routine presurgical evaluation of our patients with temporal lobe epilepsy are not good isolated predictors of surgical outcome.
Sintomas depressivos e qualidade de vida em indivíduos com epilepsia por esclerose mesial temporal
Authors: Alonso Neide Barreira , Silva Tatiana Indelicato da , Westphal Ana Carolina , Azevedo Auro Mauro , Caboclo Luís Otávio Sales Ferreira , Ciconelli Rozana Mesquita , Garzon Eliana , Sakamoto Américo Ceiki , Yacubian Elza Márcia Targas
Published: June 2012

Introdução: Dificuldades no trabalho, em relacionamentos interpessoais, familiares e sociais, a percepção do estigma, da discriminação dentre outros têm sido associados aos estados depressivos interictais, influenciando negativamente a qualidade de vida (QV) das pessoas com epilepsia. A depressão tem alta prevalência (20 a 55%) nas epilepsias, sendo vista como o fator mais importante no julgamento do paciente sobre sua QV. Objetivos: Avaliar a ocorrência de sintomas depressivos em pacientes com epilepsia do lobo temporal por esclerose mesial temporal (EMT); estudar a associação entre sintoma depressivo e QV; e entre localização da lesão estrutural e sintomas depressivos. Metodologia: Setenta pacientes com EMT em tratamento ambulatorial, foram avaliados entre junho/2003 e abril/2005. Além da anamnese clínica, exames subsidiários (EEG, vídeo-EEG, RNM), avaliação neuropsicológica, psiquiátrica, todos foram submetidos à avaliação de QV que incluiu uma entrevista semidirigida, o questionário Medical Outcomes Short-Form 36 (SF-36) e o Inventário de Depressão de Beck (BDI). Resultados: Quarenta e dois pacientes (60%) eram do sexo feminino e 28 (40%) do masculino, com média de idade de 37 anos e 26 de duração da epilepsia. Em quarenta (57%) foi constatada EMT à esquerda e em 30 (43%) à direita. Quanto à situação de trabalho, 34 (49%) encontravam-se em auxílio doença/aposentados por invalidez/ou sem qualquer atividade produtiva. Trinta e um (44%) alegaram ser o trabalho a esfera mais prejudicada pela epilepsia. Trinta e nove indivíduos (56%) apresentaram sintomas depressivos com escores mais baixos no SF-36 quando comparados àqueles sem depressão. A pontuação alta do BDI, indicativa de depressão manteve uma associação significante (coeficiente de Spearman: p < 0,001) com todos os domínios do SF-36, com exceção de capacidade funcional (CF). Não houve correlação entre o lado da EMT e os sintomas depressivos. Conclusão: A presença de depressão infuencia o julgamento individual em relação a QV. O uso sistemático de instrumentos de fácil manuseio permitiria a identificação precoce de distúrbios de humor, contribuindo significativamente para a melhoria da QV de indivíduos com epilepsia.
Optimizing Reservoir Monitoring: Improving PNL Logs in Changing Borehole Environments
Authors: Ariwodo Izu , Kanfar Majed F. , Qatari Ammar M. , Saldungaray Pablo , Rose David Alan
Published: June 2012

The growing demand for oil has emboldened producing companies to reenter old wells to further improve productivity and recovery. This requires monitoring the water saturation. Successes in reservoir saturation monitoring petrophysical analysis have increased the confidence to drill sidetracks in watered wells that have bypassed oil potential. Several techniques can be used to perform the analysis.

The Pulsed Neutron Capture (PNC) log is one of the most popular slim cased hole formation evaluation logging tools, which allow running the surveys without having to pull out the production string. Under the right conditions, the PNC logs can be run periodically in the time-lapse mode to monitor changes in water saturation and movements in the oil-water contact and gas-oil contact.

The wellbore environment may change between runs and this can complicate the analysis. For example, the borehole fluids may be different: gas, oil or brines of varying salinities. Also, changes in the downhole completion hardware can require running the logs through different tubular configurations. One has to be cognizant of all these environmental effects and appropriately correct for them to obtain the true formation properties, and to make comparisons between runs in the time-lapse analysis.

Different vendors use different correction schemes. In this paper we will discuss case studies with a methodology from one Service Company that uses a weighted database approach, which relies on characterizing the tool response in known environments. The paper shows some of the advantages and disadvantages of this technique, and in particular, when the downhole conditions deviate from the characterized environment. Alternative methodologies will be proposed to get the best possible results, based on this study. Finally, examples from Saudi Arabian wells will be shown where the computed capture cross section and neutron porosity were successfully corrected in challenging borehole conditions.
A Comprehensive EOR Study of a Highly Fractured Matured Field-Case Study
Authors: Kharrat R. , Mahdavi S. , Ghorbani Davood
Published: June 2012

Some of the Middle East fields are approaching their final stage of primary production. Most of these fields are highly fractured and carbonate in nature. One major problem is the creation of gas and water invaded zones during the history of production form such fields. Hence, the implementation of proper EOR process requires an extensive laboratory work and simulation studies.

A mature field with more than six decades of production has been considered in this study to explore all possible EOR methods. Several EOR processes such as continuous gas injection (GI), WAG (water alternative gas flooding), SWAG (simultaneous WAG), FAWAG (Foam Assisted WAG), and GAGD (Gas Assisted Gravity Drainage) process were studied in laboratory scale and simulation work. The Gas injection and GAGD were found to be unfeasible due the high fracture frequency and early gas breakthrough even with low rate of injection. However, the WAG, SWAG and FWAG were found to be more feasible. This is possibly due to mobility modification by water phase. During SWAG method all pores displaced at the same time, so that a higher ultimate recovery factor achieved sooner in comparison with WAG process. In order to have better recovery for the residual oil, FAWAG method was applied to control the injectivity of injected gas and reduce the interfacial tension (IFT) between residual oil and rock. Surfactant was chosen in different concentration of 5000, 2000, 1000, and 500 ppm. All experiments were carried out under reservoir condition. The FAWAG process was found to be more suitable process for such reservoirs due to its high recovery.

Finally the simulation study was conducted with different patterns of injection and production for all the mentioned EOR scenarios. It was found that the fractures density had an important role in the selection of the optimum pattern.
Wellbore Section Contribution in Fractured Horizontal Openhole Wells
Authors: Zhou Desheng , Li Xianwen , Zhang Kuangsheng , Yang Lijun , Mu Lijun , Li Honying
Published: June 2012

More and more horizontal wells are completed as openhole and fractured with multistage fractures. The question is what is the contribution of the openhole section to total production in a fractured horizontal openhole well? Based on actual production data of a horizontal well before and after multistage fracturing, the paper analyzes popular horizontal and fractured horizontal well correlations, and presents a new inflow performance model including the productions from the horizontal openhole section and fractures of horizontal wells.

The paper can be used to study the inflow performance of a horizontal gas well, and to check the contribution of a horizontal openhole section in a fractured well. The presented analyses can also be used to determine fracture numbers and whether to use openhole or cemented casing completion.

The paper presents that, for a pseudo steady state flow, the gas flow rate from the openhole can be calculated by Babu & Odeh correlation. For the flow from one fracture, the non-fully penetrating part of Guo and Evans correction gives around half of a reasonable rate, and it can be used by multiplying a factor 2.

The combination form the wellbore production and fracture production is not simply allocated by area percentages of wellbore wall and fracture surfaces. A correcting factor may be used to combine the flow rates from horizontal wellbore and fractures.
Evaluation of Multi-stage Fracturing by Hydrajet, Swellable Packer, and Compressive Packer Techniques in Horizontal Openhole Wells
Authors: Mu Lijun , Ma Xu , Zhang Yanming , Ling Yun , Gu Yonghon , Zhou Desheng
Published: June 2012

Horizontal openhole wells are commonly fractured by one of the three hydraulic fracturing techniques of hydrajet, swellable parker and compressive packer techniques. The paper reviews the application of 23 wells fractured by hydrajet (12 wells), swellable parker (4 wells) and compressive packer (7 wells) in tight gas sands in China. None method is overwhelming in the view of increasing production rate from the paper.

The paper presented that different treatment pressures among stages may not a signal of perfect isolation. Created traverse fracture by hydraulic stimulation may not be at the middle of two packers or at the place of opened sleeve port for swellable packer and mechanical packer stimulation. Hydrajetting is a good choice to stimulate a specific place along the entire wellbore. Unlike in vertical wells, hydrajetting may not reduce the breakdown pressure in horizontal well treatment.

The presented comprehensive comparison and discussion of the three fracturing methods will help operators understand the three methods better and accomplish production goals.
Asphaltene Deposition Study and its Effects on Permeability Reduction - A Case Study
Authors: Kharrat R. , Zargar Z. , Razavi S. M.
Published: June 2012

Asphaltene deposition affects the porosity and permeability which in turn reduces the production and raises the processing costs. Therefore, it is necessary to investigate more about the asphaltene precipitation and determining the amount of solid deposition causing the porosity and permeability reduction.

In this paper, it has been tried to overcome this need by simulating the process in one of the South-West Iranian reservoirs in which asphaltene problem has been encountered frequently. The wells under production were facing severe asphaltene choking problem and coiled tubing acid wash were done every six month to remove the deposited asphaltene. Flow assurance results for the fluid are clearly saying that oil is highly asphaltic although it is a light oil. In the other hand, wells under production always are required to keep the rate as long as possible due to economic limits and it was critical for the management to know the effect of asphaltene deposition in the reservoir formation on the flow rate and vice versa. The best way to see the effect is reservoir simulation in which asphaltene deposition is modeled.

First of all, the fluid model and asphaltene precipitation curve were prepared. Then, the reservoir static and dynamic models were generated based on the rock and fluid properties. The behavior of asphaltene during the production as precipitated, flocculated and deposited asphaltene were modeled using commercial software. In addition, the variation of permeability due to asphaltene deposition was obtained.

Asphaltene and permeability map were generated for the entire reservoir. Most of the deposition was found to form around and nearby the production wells. Minor permeability reduction was observed throughout the reservoir; however, major damage was around the wellbore. Both precipitation and deposition amounts were visible and can be reported and this ability increases the capability to decide better about the optimum production.
The Influence of Capillary Pressure on Phase Equilibrium of Mixed CO2-Water Injection into Geothermal Reservoirs Including Phase Appearance and Disappearance
Authors: Salimi Hamidreza , Wolf Karl-Heinz , Bruining Johannes
Published: June 2012

We quantify the capillary pressure effect on the phase equilibrium of the CO2-water system. Our interest is in the capillarypressure range between 0 and 100 bars for temperatures between 293 and 372 K and bulk (wetting-phase) pressures between 25 and 255 bars. For this purpose, we have implemented the capillary pressure effect in the PRSV equation of state. Inclusion of capillary pressure in the phase equilibrium of the CO2-water system makes it possible to determine the capillary-pressure effect on the CO2 storage capacity and heat-energy recovery for CO2-water injection into geothermal reservoirs. We illustrate the process using a 2D model of the geothermal reservoir in the Delft Sandstone Member, below the city of Delft (The Netherlands). The process involves phase transitions between single-phase and two-phase regions. To deal with phase appearance and disappearance, we have applied a new and effective solution approach, the so-called nonisothermal negative saturation?? (NegSat) solution approach.

The results show that the capillary pressure promotes evaporation. In the pressure and temperature range of our interest, capillary pressure reduces the CO2 solubility in water and the aqueous-phase density up to 64% and 1.3%, respectively, whereas it increases the water solubility in the CO2-rich phase and the CO2-rich-phase density up to 3,945% (40.5 times) and 1,544%, respectively. Capillary pressure shifts the CO2 liquid-vapor transition and consequently the upper critical point of the CO2-water system to a lower pressure. The intensity of the shift depends on the value of the capillary pressure and the bulk (wetting-phase) pressure. For instance, the CO2 liquid-vapor transition at T = 293 K occurs approximately at 60 bars for Pc = 0 bars, whereas it occurs at 15 bars for Pc = 45 bars.

For mixed CO2-water injection into the geothermal reservoir (200 bars < P < 260 bars, 290 K < T < 360 K), inclusion of the capillary pressure effect in the phase-equilibrium behavior does not significantly alter the capillary CO2-trapping mechanism. In other words, CO2 banks are mainly formed in the highly permeable zones that are surrounded by less permeable zones. However, for injected CO2 concentrations close to the bubble point, the effect of capillary pressure on the phase equilibrium reduces the heat recovery by 37% and the CO2-storage capacity also by 37%. For overall injected CO2 mole fractions between 4% and 13%, the reduction in the heat recovery and CO2-storage capacity is 10%. Based on simulations, we construct a plot of the recuperated heat energy versus the maximally stored CO2 for a variety of conditions; we compare the results including and excluding the effect of capillary pressure in the phase-equilibrium calculations.
Investigation of the Applicability of Thermal Well Test Analysis in Steam Injection Wells for Athabasca Heavy Oil
Authors: Ghahfarokhi Ashkan Jahanbani , Jelmert Tom Aage , Kleppe Jon , Ashrafi Mohammad , Souraki Yaser , Torsaeter Ole
Published: June 2012

Thermal well testing of steam injection wells offers an inexpensive quick method to estimate flow capacity and swept volume in thermal recovery processes. Pressure falloff tests are commonly used for this purpose. Estimation of steam zone properties and swept volume from falloff test data in this study is based on the theory assuming a composite reservoir with two regions of highly contrasting fluid mobilities and the interface as an impermeable boundary. Consequently, the swept zone acts as a bounded reservoir for a short duration, during which the pressure response is characterized by pseudo steady state behavior.

The purpose of this study is to evaluate the applicability and accuracy of thermal well test analysis method and effects of different parameters on results. Pressure falloff testing is simulated using a numerical thermal simulator. The generated pressure falloff data are then analyzed to calculate swept volume and reservoir parameters. Different gridblock models are considered.

Viscosity of Athabasca heavy crude sample was measured in the lab using a rotational viscometer up to 300°C. Bitumen sample molar mass was measured by cryoscopy. Density at standard conditions was measured by a density measuring cell. These data were used as input for numerical simulation purposes.

Results of this work show that the swept volume, swept zone permeability and skin factor can reasonably be estimated from pressure falloff tests. The effects of gravity, dip, permeability anisotropy and irregular shapes of swept zones are studied. It can be seen that these factors do not greatly affect the estimated results. Results of 3D models show that the estimation of permeability and steam swept volume depends on the vertical positions where pressure data are measured. It is also found that real gas analysis does not substantially improve the calculation accuracy and the pressure analysis technique suffices for all practical purposes.
Removal Efficiency of Water-Based Drill-In Fluid Filter Cake Using Polylactic Acid
Authors: Elkatatny S. M. , Nasr-El-Din H. A.
Published: June 2012

Water-based drilling fluids consisting of xanthan gum, starch, sized calcium carbonate and salt particles have been used to drill horizontal wells. Available chemical methods of removing filter cake like mineral acids, esters, oxidizers, and chelating agents are limited at certain conditions.

Drilling fluid was designed based on calcium carbonate particles and an ester of lactic acid. The objective of the latter is to remove calcium carbonate once the drilling operation is complete and there is a need to remove the filter cake. Extensive lab work was done to: 1) determine thermal stability of the drilling fluid (70-72 pcf) for 24 hrs, 2) characterize the filter cake using computer tomography, 3) assess potential formation damage for different rock types (limestone and sandstone) using a modified HPHT filter press, and 4) determine the removal efficiency of the filter cake and the return permeability.

The results obtained showed that the drill-in fluid has stable rheological properties up to 250°F over 24 hrs. A CT scan showed that the filter cake contained two layers, one layer close to the rock surface, which contained a mixture of calcium carbonate and acid-precursor, and one layer close to the drilling fluid that contained a mixture of XC-polymer and starch. The polymer layer was removed by using 10% solution of alpha amylase. The rest of the filter cake was removed by lactic acid that was produced from the hydrolysis of the ester. The removal efficiency of the filter cake was nearly 100% and the return permeability was about 100%, when using a ratio of polylactic acid to calcium carbonate 3 to 1. The decrease in the CT number of the core after the removal process indicated that the filter cake was completely removed and no formation damage occurred. This paper will discuss the development of this new drilling fluid and will give recommendations for field applications.
Static and Dynamic Assessment of DFN Permeability Upscaling
Authors: Ahmed Elfeel M. , Geiger S.
Published: June 2012

Nearly half of the remaining petroleum reserves are contained in naturally fractured reservoirs (NFR). An accurate estimate of the effective fracture permeability tensor is a key to the successful prediction of oil recovery from NFR. Standard workflows nowadays employ discrete fracture network (DFN) modeling and analytical or flow-based methods to upscale fracture permeabilities. However, DFN modeling imposes some important challenges, which can cause great uncertainty in the effective permeability tensor and subsequent recovery prediction: Analytical upscaling methods, which are commonly used due to computational efficiency, are inaccurate for poorly connected fracture networks. Flow-based upscaling methods depend on boundary conditions and are computationally expensive. Defining the optimum grid size for either method is also very difficult. In addition, DFN upscaling is often driven by practical issues such as time constrains and computational limitations, leaving little room to investigate the effects of upscaling methods and grid size.

In this paper we utilize features in leading DFN simulators employed in standard industry workflows for computing effective permeability tensors with flow-based and analytical methods. We use two realistic dataset from fractured formations of onshore reservoirs in our assessment. Not surprisingly, there is up to three orders of magnitude variation in the effective permeability based on the chosen upscaling method and perceived optimum grid cell size. This has tremendous impact on predicted recovery rates and ultimate recovery; ultimately uncertainty in upscaling can mask uncertainty in the geological model. We hence introduce a new simulation technique, Discrete Fracture and Matrix (DFM) modeling, which accounts accurately for flow in the fractures and rock matrix as an efficient alternative for computing effective permeability tensors as it allows us to assess the accuracy of classical DFN upscaling approaches, which all help reducing uncertainty in recovery prediction.
Application of Injection Fall-Off Analysis in Polymer flooding
Authors: van den Hoek P. J. , Mahani H. , Sorop T. G. , Brooks A. D. , Zwaan M. , Sen S. , Shuaili K. , Saadi F.
Published: June 2012

Polymers exhibit non-Newtonian rheological behavior, such as in-situ shear-thinning and shear-thickening effects. This has a significant impact on pressure decline signature as exhibited during Pressure Fall-Off (PFO) tests. Therefore, applying a different PFO interpretation method, compared to conventional approaches for Newtonian fluids is required.

This paper presents a simple and practical methodology to infer the in-situ polymer rheology from PFO tests performed during polymer injection. This is based on a combination of numerical flow simulations and analytical pressure transient calculations, resulting in generic type curves that are used to compute consistency index and flow behavior index, in addition to the usual reservoir parameters (kh, faulting, etc.) and parameters relating to (possible) induced fracturing during injection (fracture length and height). The tools and workflows are illustrated by a number of field examples of polymer PFO, which will also demonstrate how the polymer bank can be located from the data.
Overdisplacing Propped Fracture Treatments—Good Practice or Asking for Trouble?
Authors: van Gijtenbeek Klaas , Shaoul Josef , de Pater Hans
Published: June 2012

One of the major issues with the development of unconventional ultratight shale-gas reservoirs is related to concerns about underdisplacing or overdisplacing hydraulic proppant-fracture treatments in multiple-zone completions in horizontal wells.

In recent years, a very large number of multistage propped-fracture treatments in horizontal wells in ultratight shale-gas reservoirs have been overdisplaced to obtain a clean wellbore and avoid problems with the hardware (especially pump-down plugs) used for rapid multizone completions. Because cleanout treatments can usually be avoided by these overdisplacements, multiple treatment stages can be performed more quickly, which saves time and minimizes other added costs. However, this practice might result in poor communication between the propped fractures placed in the reservoir and the wellbore.

In some situations, such as when the rock strength is sufficient to prevent closure of nonpropped fracture areas, overdisplacing a treatment could result in a very high conductivity region at the wellbore. There is certainly a limit to the length of an unpropped fracture that could stay open for a significant time. This mechanism is similar to what has been seen in some wells with proppant production, where well productivity has increased following proppant production. Proppant production might create some open channels in the proppant pack near the perforations that remain open.

This paper discusses current overdisplacement practices and tries to address if and when overdisplacing fractures in shale- or tight-gas reservoirs could have a net positive or a negative effect on production.
Transient Gas Flow in Unconventional Gas Reservoirs
Authors: Wu Yu-Shu , Wang Cong , Li Jianfang , Fakcharoenphol Perapon
Published: June 2012

Unconventional gas resources from low-permeability formation, i.e., tight and shale gas, are currently received great attention because of their potential to supply the world with sufficient energy for decades to come. In the past few years, as a result of industry-wide R&D effort, progresses are being made towards commercial development of gas and oil from such unconventional resources. However, studies, understandings, and effective technologies needed for development of unconventional reservoirs are far behind the industry needs, and gas recovery from those unconventional resources remains low (estimated at 10-30% of GIP).

Gas flow in low-permeability unconventional reservoirs is highly nonlinear, coupled by many co-existing processes, e.g., non-Darcy flow and rock-fluid interaction within tiny pores or micro-fractures. Quantitative characterization of unconventional reservoirs has been a significant scientific challenge currently. Because of complicated flow behavior, strong interaction between fluid and rock, the traditional Darcy law may not be applicable for describing flow phenomena in general. In this paper, we will discuss a general mathematical model of gas flow through unconventional porous media and use both numerical and analytical approaches to analyze gas flow in unconventional reservoirs. In particular, we will present analytical and numerical solutions of incorporating Klinkenberg effect, non-Darcy flow with threshold pressure gradient, and flow behavior in pressure sensitive media. We will discuss the numerical implementation of the mathematical model and show applications of the mathematical model and solutions in analyzing transient gas flow in conventional reservoirs.
Proper Design Criteria of Microemulsion Treatment Fluids for Enhancing Well Production
Authors: Quintero Lirio , Jones Thomas A , Pietrangeli Gianna A.
Published: June 2012

When newly drilled oil and gas wells fail to reach the expected production levels, near-wellbore damage may have resulted from fluid incompatibility, poor fluid/rock interaction and/or mechanical damage. These problems may also occur during remediation or stimulation operations, if the treatment fluid is not properly designed. The principal formation damage mechanisms that lead to these problems are in-situ emulsions, wettability changes, water blocks and scale formation. It is recognized that such reservoir damage can be removed or prevented using microemulsion technology that leads to more productive oil and gas wells.

The challenge is to design and select an optimized microemulsion system based on the reservoir conditions, such as the bottomhole temperature and the individual compositions of the crude oil, formation water, and the drilling and completion fluids. A well-designed treatment fluid should provide ultra-low interfacial tension, high oil solubilization and total compatibility with all fluids it encounters. The selection of the optimum formulation for a specific application requires a systematic study of the phase behavior of brine-surfactant-oil systems as a function of temperature and its final composition, including the salt, surfactants, co-surfactants and an optional acid.

This paper provides a comprehensive discussion of the phase behavior obtained with the brine/surfactant/oil systems used in microemulsion formulations for formation damage prevention and removal. Laboratory tests results and field applications in openhole and cased-hole completed wells have proven that the microemulsion treatment fluids are successful in the field, if there is a systematic analysis of phase behavior that identifies and defines the treatment fluid phase boundaries.
Decision Making Under Uncertainty in EOR: Applying the Least Squares MonteCarlo Method in Chemical EOR Implementation
Authors: Alkhatib A. , Babaei M. , King P. R.
Published: June 2012

This study introduces a decision making evaluation method for flexibility in chemical EOR. The method aims to capture the effects of dynamic uncertainties both technical and economic and produce a near-optimal policy with respect to these uncertainties as they vary with time. The evaluation method used was the Least-Squares MonteCarlo(LSM) method which is best suited for evaluating flexibility in project implementation. The decision analysed was that of finding the best time to initiate surfactant flooding during the life time of a field under uncertainty. The study was conducted on two reservoir models: 3-D homogeneous model and a 2-D heterogeneous model. The technical uncertainties considered were the residual oil saturation to the surfactant flood, surfactant adsorption and reservoir heterogeneity while the main economic uncertain parameters considered were oil price, surfactant cost and water injection and production costs. The results show that the LSM method provides a decision making tool that was able to capture the value of flexibility in surfactant flooding implementation. The LSM method provides great insight into the effect of uncertainty on decision making which can help mitigate adverse circumstances should they arise. The results found that the optimal policy obtained was reliable and that heterogeneity does affect the optimal policy. It was also possible to consider the value of information using this method.
Capillary Pressure: Is It Critical for Investment Decisions? Case Study of Gas Condensate Reservoir Underlain with Water
Authors: Fayzullin Maksim , Nasibullin Artur , Yazkov Alexey , Kolbikov Sergey
Published: June 2012

The paper highlights the importance of adequate characterization of capillary pressure effects when preparing a development plan for a greenfield gas condensate reservoir with a large transition zone (TZ).

Capillary pressure data from centrifuge or porous plate (semi-permeable membrane) are used to characterise the transition zone. It is essential that a representative set of sample measurements is obtained. Core laboratories are not capable to keep initial pressure-temperature conditions during capillary pressure measurements. Hence, the conversion from surface to reservoir becomes uncertain. Conversion utilizes interfacial tension and wettability angle which are quite unknown and can be predicted using different P-T charts. Finally saturation model depends on the way of: characterization - discrete Rock Types (RT) or tuned-up Continuous Functions (Leverett, Amaefule etc.); matching log saturation profile with the one observed in the model; welltest playback in terms of mobile water and drained volumes.

In this study, the authors present a systematic workflow on how capillary pressure should be incorporated in a dynamic simulation model pointing out example pitfalls and giving validation tips. The illustrated case shows that if one of the steps is missed or wrong assumptions are made, then the TZ and the production potential will be incorrect. In our example, the discretization of connate water saturation and capillary pressure curves on early stages resulted to 8% underestimation of GIIP. Moreover, results indicated that uncertainty in conversion of capillary curves (from surface to reservoir) gives 15-20% differences in outcomes (depending on development scenario). Also it demonstrates a strong impact on the length of production plateau, rate of wellhead pressure decline, compression start-up which are vital aspects for the development concept, especially during front-end-loading stage of the project plan. We feel that the procedures presented here (both for engineers and management) can serve as a guide for QC and possible failures when they are not applied.
Improving Well Cementing Quality with an Environmentally Preferred Multifunctional Polymer
Authors: Brandl Andreas , Bray Windal Scott , Magelky Christina
Published: June 2012

A modified cellulose-based polymer has been tested according to API recommended practices in various cement slurries and was identified to have multiple beneficial functions in addition to be environmentally friendly. Test results demonstrate that this single additive controls fluid loss better than commonly used fluid loss additives at temperatures up to 170 °F while also controlling free fluid and performing as an extender. In addition, it was found to work as a foam stabilizer and gas control agent in cement slurries, which was not observed for any other cellulose-based polymers tested. The modified cellulose-based polymer also exhibits less slurry viscosification, which facilitates surface mixing and pumping of the corresponding cement slurries. This paper will describe test procedures, discuss test results, and demonstrate that a single modified cellulose-based polymer can replace several additives in a cement system to adjust the required cement slurry performances for optimum placement and properties in the wellbore. These findings are accomplished by a case history showing the successful application of the modified cellulose-based polymer for a deepwater cementing operation in the South China Sea. The here presented multifunctional biopolymer simplifies cement slurry design and operations contributing to higher quality cement jobs.