Zero-thickness interface model with chemical degradation by acid attack

Carbon dioxide (CO2) storage in abandoned oil/gas reservoirs is considered a viable alternative to reduce greenhouse gas emissions to the atmosphere. An important element of the risk associated with long-term CO2 storage is the loss of integrity of the cement seals of the abandoned wells in the reservoir. Among others, one possible cause of loss of integrity is the degradation of the oil-well cement due to the acid attack of the carbonated brine in the reservoir. In previous studies, the authors have developed a diffusion-reaction model for simulating this degradation process. In order to study possible coupled Chemo-Mechanical (CM) mechanisms, this model will be coupled with an existing mechanical model. For this purpose, in this paper, an existing constitutive law for zero-thickness interface, based on the theory of elasto-plasticity with concepts of fracture mechanics, is modified to incorporate the effect of chemical degradation on the mechanical strength parameters. Preliminary results obtained with this new constitutive law are presented, in order to illustrate the main aspects of the proposed constitutive law, as well as a possible C-M degradation mechanism that should be considered in the long-term safety assessment of CO2 geological storage projects

Comprensión de las prácticas educativas que median la convivencia escolar institución educativa Augusto Zuluaga Patiño y Fundación Universitaria del Área Andina de la ciudad de Pereira

El trabajo investigativo que aquí se presenta, tiene como objetivo responder a la pregunta: ¿Cuáles prácticas educativas median la convivencia escolar? Para dar respuesta a dicho interrogante se ha planteado un objetivo general enmarcado en la comprensión de dichas realidades sociales. La investigación se realizó desde una perspectiva cualitativa, con un enfoque comprensivo - interpretativo, donde se analizaron las dinámicas de los actores: estudiantes, docentes, directivos y padres de familia. Desde el punto de vista teórico, la investigación se apoyó en diferentes autores que desde la realidad observada pudieron aportar a las categorías centrales. En prácticas educativas, los investigadores se apoyaron en la teoría que plantean Kemmis (1996), Carr (1996), Perrenoud (2001); en la categoría de convivencia, en el tema de ciudadanía, se apoyaron en Dewey (2004) y Mockus (2004), y en el aspecto educativo asumieron como autores principales a Chaux (2012), Ortega (2008) y Torrego (2007). La metodología utilizada en la investigación fue el Método Etnográfico como estructura central para lograr dar respuesta a la pregunta planteada. Las técnicas que se trabajaron, en relación con la recolección de información, fueron: la observación sistemática y la entrevista; los instrumentos de recolección fueron el diario de campo, la rejilla de observación y el cuestionario semi estructurado; y, para el análisis de la información, se trabajó con codificación abierta, axial, selectiva, utilizando el programa Atlas Ti versión 7.0 para el procesamiento de la información. En una fase posterior hubo interpretación de los hallazgos para la construcción de sentido.Se llegaron a unas categorías comunes y otras diferentes a fin de responder a la pregunta de investigación, generando unas conclusiones y recomendaciones temáticas y desde el punto de vista social.The research work presented here aims to answer the question: What educational practices mediate school life? To answer this question we have raised a general goal framed in understanding these social realities. The research was conducted from a qualitative perspective, with a comprehensive approach - interpretative, which analyzed the dynamics of the actors: students, teachers, administrators and parents. From a theoretical point of view, the investigation was based on different authors from the observed reality that could contribute to the central categories. In educational practice, the researchers relied on the theory posed by Kemmis (1996 ) , Carr (1996 ) , and Perrenoud (2001 ), in the category of coexistence , on the issue of citizenship , they relied on Dewey (2004) and Mockus ( 2004 ), Finally, on the educational aspect the principal authors were Chaux (2012 ) , Ortega (2008) and Torrego (2007). The methodology used in the case studies was the Ethnographic Method as a central structure to achieve and try to answer the question posed. The techniques used, in relation to data collection were: systematic observation and interview, data collection instruments used were a field diary, grid observation and a semi structured questionnaire and, for the analysis of the information, we worked with open coding , axial , selective , using Atlas Ti software version 7.0 for information processing . At a later stage there was interpretation of the findings for the construction of meaning. We came to some common categories and other different ones for the purpose of answering the research question, generating some conclusions and recommendations from a social standpoint

Production and supervision of Spanish Doctoral Theses on Advertising: 1971-2010

Este estudio analiza la producción y dirección de tesis doctorales sobre publicidad en las universidades españolas. No sólo en las universidades que cuentan con facultades de Comunicación o Información, sino en todas aquellas que cuentan con alguna tesis doctoral sobre el tema y cuyo director figura de forma expresa. Para ello, se ha trabajado con una producción total de 260 tesis doctorales durante un período que abarca desde la creación de la Licenciatura de Publicidad en la universidad española en 1971 hasta el año 2010. Para los diferentes análisis se han aplicado técnicas bibliométricas. En el análisis se prestó atención a la evolución de la producción anual de las tesis doctorales, la distribución de la producción en las universidades, y en las facultades y departamentos responsables de las tesis doctorales. Finalmente, se analizó la producción de los directores de las tesis; así como los niveles de colaboración o cooperación en la dirección. El número de directores asciende a doscientos catorce. Las tesis dirigidas por más de un director se elevan a 25.This study analyses the production and supervision of doctoral theses on advertising in Spanish universities. Universities with Faculties of Communication or Information Science have been included, as have any others that had theses on advertising and in which the supervisor fi gures expressly. We worked with 260 doctoral dissertations from the period ranging the creation of the BA in Advertising in Spain in 1971 until 2010. Bibliometric techniques were applied for performing the different analyses. During the study we focussed on the evolution of the annual production of doctoral theses, the distribution of production among the universities, and also among the faculties or departments responsible for doctoral theses. Finally, we analysed the scholarly production of the supervisors themselves, as well as the levels of collaboration or cooperation during the supervision. A total of two hundred and fourteen supervisors were studied; twenty five theses had more than one supervisor.PublicadoPublicad

A survey using constraints to decision-making for fault tolerance in Business processes

Sometimes the business processes do not work how it is expected. In these cases, a diagnosis process has to be executed to determine the responsible activity or activities of the fault in order to substitute it or them for a correct activity. The aim of this paper is describe the necessary steps to find out another service that can replace it in an efficient way. In order to automate the search and substitution of activities, we propose to describe the functionality of the tasks using constraints, making easier the determination of the possible activities that could substitute everyone faulty activities in the business process. In this paper, it is also analyzed how to adapt the communication protocol with XML messages to a behavior described using constraints.Junta de Andalucía P08-TIC-04095Ministerio de Ciencia y Tecnología TIN2009-1371

Diffusion-reaction modelling of the degradation of oil-well cement exposed to carbonated brine

The essential aspects of a diffusion-reaction model in development for the degradation process of oil-well cement exposed to carbonated brine are presented in this paper. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the hardened cement paste pore solution, complemented by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. A sensitivity analysis of some parameters of the model is presented to illustrate the capabilities to reproduce realistically some aspects of the degradation process.Postprint (published version

Celdas de combustible con convertidores elevadores para energías alternativas

The need for energy in the world has led to the search for new ways of electric power generation, among which is the use of fuel cells as a renewable source that does not contribute to environmental pollution and has high efficiency in energy conversion. In this type of technology the system suffers voltage fluctuations due to the connected loads. Booster converters of boost type are used, which allow to regulate the tension to an optimal value, without great fluctuations. We chose the design of the PI type control by means of the state space method to obtain the transfer functions, and the Routh-Hurwitz criterion to obtain the constants of the PI controller. A fuel cell system of 1 kW was simulated keeping the regulator output voltage at 48 V constant with an overvoltage not greater than 30% of the desired value.The need for energy in the world has led to the search for new ways of electric power generation, among which is the use of fuel cells as a renewable source that does not contribute to environmental pollution and has high efficiency in energy conversion. In this type of technology the system suffers voltage fluctuations due to the connected loads. Booster converters of boost type are used, which allow to regulate the tension to an optimal value, without great fluctuations. We chose the design of the PI type control by means of the state space method to obtain the transfer functions, and the Routh-Hurwitz criterion to obtain the constants of the PI controller. A fuel cell system of 1 kW was simulated keeping the regulator output voltage at 48 V constant with an overvoltage not greater than 30% of the desired value

Practicum management and enhancement through an online tool in foreign language teacher education

Practicum is an essential and meaningful part of teacher education but due to the great diversity of educational programmes worldwide, their nature and quality depend too much on each particular situation. There is an urgent need to unify and upgrade practicum formats. This paper reports a proposal for technology enhancement and structure reconfiguration of the practicum within the wider curricula. Added to that, we present an Interactive Digital Notepad (IDN) prototype, based on Kanban and powered up by Trello, as an optimal solution to the challenges posed in practicum management in foreign language teacher education programmes. Circumscribed to the Spanish educational context, this IDN is an online tool designed to improve the monitoring of the learning process in order to foster interactive and effective communication among the participants, and to promote critical thinking and autonomy. Results are promising and further steps for further improvement and implementation are outlined.Erasmus + VIRTEACH project (Project Reference: 2018-1-ES01-KA203-050045)

3D zero-thickness interface model for fracture of cement-based materials with chemical degradation

In the framework of the Finite Element Method, zero-thickness interface elements have been widely used to model fracturing processes in quasi-brittle materials in a broad variety of problems. In particular, interface elements equipped with elastoplastic constitutive laws that account for the softening of the material strength parameters due to the fracturing mechanical work has been proved to accurately reproduce observed fracture propagation behaviour in concrete. Along this line, this paper presents the extension of an existing constitutive law of this kind to include the effect of chemical degradation of the material in the formation of fractures. The law is defined in terms of the normal and shear stresses on the average plane of the crack and the corresponding normal and shear relative displacements. A hyperbolic cracking (plastification) surface in the stress state determines the crack initiation. The softening of the cracking surface is governed by two history variables: an internal variable that accounts for the dissipated fracturing (plastic) work, and an external variable to be provided by a chemical degradation model that accounts for the effect of chemical degradation on the strength parameters. After a detailed discussion of the formulation, the main characteristics of the proposed law are illustrated with a number of academic examples for different combinations of mechanical loading and chemical degradation sequences. The model is finally validated against experimental results from the literature consisting of three-point bending tests performed on mortar samples previously exposed to an aggressive solution for different time periods.This research is supported by grants BIA2016-76543-R from MEC (Madrid), Spain, which includes FEDER, Spain funds, and 2017SGR-1153 from AGAUR (Generalitat de Catalunya, Barcelona), Spain. The first author thanks the scholarship 2017FI-B00559 received from AGAUR (Generalitat de Catalunya, Barcelona), Spain.Peer ReviewedPostprint (published version

Effect of long-term pore pressure evolution on the integrity of cement plugs of abandoned oil wells in CCS sites

In the context of Carbon Capture Storage (CCS) in abandoned hydrocarbon reservoirs, a preliminary study of the effects of pore pressure evolution on the integrity of oil-well cement seals is performed. A 2D cross-section of the sealed oil-well system (caprock-external cement sheath-steel casing-cement plug) is analysed along its service-life (injection/production activities and abandonment) using the Finite Element Method with zero-thickness interface elements to represent potential cracks. In particular, these elements are pre-inserted in the analysis in between the contacts of caprock-external cement sheath, external cement sheath-casing and casing-cement plug. The results presented show that, depending on the initial state and range of pressure evolution, the different interfaces considered may open or close in a non-trivial manner during the pressure return process. This seems to indicate the importance of considering carefully the pressure return process and subsequent effective stresses evolution in abandoned reservoirs recycled to CCS, in order to avoid that new cracks in well cement seals may lead to potential CO2 leakage in the storage site.This research is supported by grants BIA2016-76543-R from MEC (Madrid), which includes FEDER funds, and 2017SGR-1153 from AGAUR (Generalitat de Catalunya, Barcelona). The first author thanks the scholarship 2017FI-B00559 received from AGAUR (Generalitat de Catalunya, Barcelona).Postprint (published version

Modelling acid attack of oilwell cement exposed to carbonated brine

A diffusion-reaction model for the carbonation process of oilwell cement exposed to carbonated brine under CO2 geological storage conditions is presented. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the pore solution of the hardened cement paste, complemented by two diffusion-only field equations for chloride and alkalis concentrations, and by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. The model is used to simulate experimental tests performed by Duguid and Scherer (2010), leading to promising results indicating that the fundamental aspects of the phenomenon are captured.Peer ReviewedPostprint (author's final draft