1,720,952 research outputs found
Computational Modeling of Hydro-Electro-Mechanical Flow During CO2 Geosequestration
No full textCO2 geo-sequestration (CGS) is considered to be a feasible technology for reducing the amount of CO2 emission into the atmosphere. Selection of an appropriate reservoir is vital and requires appropriate knowledge of the involved phenomena and processes. In a CO2 geo-sequestration process, carbon dioxide goes through mainly four storage (trapping) mechanisms: structural and stratigraphic trapping, residual trapping, solubility trapping and mineral trapping. In this study, focus is placed on modeling the first trapping mechanism, together with corresponding deformation and electrokinetic flow. Multiphase fluid flow due to injection of CO2 in an unsaturated reservoir is accompanied by continuous redistribution of pore pressure and effective stress, causing local and regional deformations and probably major uplifting or subsidence. This flow is also accompanied by electrokinetic flow. In such a system, electrokinetic potentials occur due to the interaction between the formation fluid and the mineral grains. Due to pressure gradients, the flow of the pore fluid produces an advective electric current: such a flow generates an electric field, which produces a counter electric current through the interface, known as the self-potential (SP). Since the electrical conductivity of CO2 is lower than that of the formation brine, it can be detected by measuring the self-potential. Based on this, the SP can be used for monitoring CO2 plume movement, a necessary procedure to ensure that geologic sequestration is both safe and effective. In spite of the versatility of the available numerical tools, attempts to model CO2 geo-sequestration in a region and considering events occurring in local areas lead to enormous demands for computational power. This makes the development of numerical tools for CO2 geo-sequestration not only difficult, but rather expensive. In this study, the governing field equations are derived based on the averaging theory and solved numerically based on a mixed discretization scheme. In this scheme, variables exhibiting different nature are treated using different numerical discretization techniques. Techniques such as the standard Galerkin finite element method (SG), the extended finite element method (XFEM), the level-set method (LS) and the Petrov-Galerkin method (PG) are integrated in a single numerical scheme. SG is utilized to discretize the deformation and the diffusive dominant field equations, and XFEM, together with LS, are utilized to discretize the advective dominant field equations. The level-set method is employed to trace and locate the CO2 plume front, and the XFEM is employed to model the associated high gradient in the saturation field front. The use of XFEM for the advective field leads to a computationally efficient, stable and effectively mesh-independent discretization. However, it gives rise to an extra degree of freedom. The use of SG for the deformation and the diffusive fields requires only standard degrees of freedom, limiting the total number of degrees of freedom and making the scheme computationally efficient. Several verification and numerical examples are presented for both homogenous and fractured reservoirs. The examples demonstrate the capability of the proposed mixed discretization model to simulate challenging, coupled analyses. It has been shown that this model is capable of solving problems, which typically involve several state variables with different transient nature, using relatively coarse meshes.Structural EngineeringCivil Engineering and Geoscience
A mixed discretization scheme for CO2 sequestration in fractured porous media (abstract)
No full textStructural EngineeringCivil Engineering and Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
XFEM-level set model for CO2 sequestration (abstract)
No full textStructural EngineeringCivil Engineering and Geoscience
An efficient computational model for CO2 flow in porous media
Get PDFThis paper presents an efficient computational model for the simulation of fully coupled two-phase flow in a deformed partially saturated formation. Focus is placed on modeling the flow of a CO2 plume in a porous medium. The numerical procedure is based on coupling between the Level-set method (LS) and the extended finite element method (XFEM). The level set is employed to define the location of the front between injected CO2 and existing formation water. A streamline upwind Petrov-Galerkin method is utilized to stabilize the possible occurrence of spurious oscillations in the advection of the CO2 front. The XFEM is employed to model the gradient in the degree of saturation at the front. This is done by decomposing the saturation field into a continuous part and a discontinuous part. The latter is enhanced by the use of a local enrichment function which is calculated on the basis of the Level-set function. Numerical implementation of the method is discussed and numerical examples are given.Structural EngineeringCivil Engineering and Geoscience
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A Hydromechanic-Electrokinetic Model for CO2 Sequestration in Geological Formations
Get PDFIn this contribution, a finite element model for simulating coupled hydromechanic and electrokinetic flow in a multiphase domain is outlined. The model describes CO2 flow in a deformed, unsaturated geological formation and its associated streaming potential flow. The governing field equations are derived based on the averaging theory and solved numerically based a mixed discretization scheme. The standard Galerkin finite element method is utilized to discretize the deformation and the diffusive dominant field equations, and the extended finite element method, together with the level-set method, is utilized to discretize the advective dominant field equations. The level-set method is employed to trace the CO2 plume front, and the extended finite element method is employed to model the high gradient in the saturation field front. The mixed discretization scheme leads to a highly convergent system, giving a stable and effectively mesh-independent model. The capability of the model is evaluated by verification and numerical examples. The numerical analysis shows that the streaming potential peak moves with the saturation front, and hence, measuring the streaming potential can be utilized for monitoring CO2 flow remotely.Structural EngineeringCivil Engineering and Geoscience
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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