1,720,953 research outputs found
Model-reduced gradient-based history matching
No full textSince the world's energy demand increases every year, the oil & gas industry makes a continuous effort to improve fossil fuel recovery. Physics-based petroleum reservoir modeling and closed-loop model-based reservoir management concept can play an important role here. In this concept measured data are used to improve the geological model, while the improved model is used to increase the recovery from a field. Both problems can be formulated as optimization problem, i.e. history matching identifies the parameter values that minimize an objective function that represents the mismatch between modeled and observed data while production optimization identifies wells controls that maximize the total oil recovery or monetary profit. One of the most efficient class of methods to solve history matching and production optimization problems are gradient-based methods where the gradients are calculated with the use of an adjoint method. The implementation of the adjoint method for parameter estimation and control optimization is, however, very difficult if no Jacobians of the model are available. This implies that there is a need for gradient-based, but adjoint-free optimization methods. A requirement becomes even more pressing if reservoir simulation is combined with another simulation, e.g. simulation of geomechanics or rock physics, with a code for which no Jacobians are available. The research objective of this thesis was to evaluate the performance of a model-reduced gradient-based history matching routine that does not require a difficult implementation and involves the reduction of the reservoir system. Additionally, the use of model-reduced method for production optimization of a reservoir operating under induced fracturing conditions was considered. In history matching problems one deals with a large number of uncertain parameters and very sparse observations, while in the production optimization one controls a large dimensional system by adjusting a limited number of controls. Consequently, the values of many model parameters cannot be verified with measurements due to a relatively few information content present in them, while in the production optimization only a limited part of the system can be indeed controlled. In this thesis we proposed a new method inspired by the results in reduced order modeling (ROM) and system-theoretical concepts of controllability and observability of the reservoir system. The new approach assumes that the reservoir dynamics relevant for history matching or production optimization can be represented accurately by a much smaller number of variables than the number of grid cells used in the simulation model. Consequently, the original (nonlinear and high-order) forward model is replaced by a linear reduced-order forward model and the adjoint of the tangent linear approximation of the original forward model is replaced by the adjoint of a linear reduced-order forward model. The reduced-order model is constructed by means of the Proper Orthogonal Decomposition (POD) method or Balanced Proper Orthogonal Decomposition (BPOD) method. The reduced-order model is not, however, obtained by the projection of the nonlinear system of equations as in the conventional projection-based ROM techniques, but instead it is approximated in the reduced subspace. The conventional POD method requires the availability of the high-order tangent model, i.e. of the Jacobians with respect to the states which are not available. The model-reduced method obtains a reduced-order approximation of the tangent linear model directly by computing approximate derivatives of the reduced-order model. Then due to the linear character of the reduced model, the corresponding adjoint model is easily obtained. The gradient of the objective function is approximated and the minimization problem is solved in the reduced space; the procedure is iterated with the updated estimate of the parameters if necessary. The POD-based approach is adjoint-free and can be used with any reservoir simulator, while the BPOD-based approach requires an adjoint model but does not require the Jacobians of the model with respect to uncertain parameters or controls. At first the model-reduced method was applied to history matching problems and was evaluated based on its computational efficiency and robustness. In order to make a valuable judgment this approach was compared to the classical adjoint-based method, which was available for the estimation of the permeability field. Permeabilities are described at each cell of the model, and therefore they need to be re-parameterized. The KL-expansion was used to reduce the parameters space. The significant reduction of the dimension of the dynamic reservoir model and parameter space made the approximation of the reduced-order system feasible in acceptable computation time. The pressure field required relatively low number of patterns which modeled mostly the changes around the wells. The saturation field required much more patterns and they modeled mostly the moving front of the saturation field. In the first studies simplistic reservoir models were used, for which the model-reduced approach showed to perform very well. The obtained estimates of the permeability field significantly improved compared to the prior fields and gave the acceptable history-matches; the quality of the prediction capabilities of the estimated models were very high and comparable to those obtained by the classical adjoint-based approach. The POD-based method was approximately twice as expensive as the classical approach, but the BPOD-based method was comparable to the adjoint-based method. Moreover, both methods were considerably cheaper than the finite difference approach. These preliminary results were the first applications of the model-order reduction to history matching problems. After this proof of concept, further studies were carried on more complex and larger models. The proposed method was capable to obtain satisfactory match with a computational efficiency about five times lower than the adjoint-based method. Similarly, an improvement in the prediction was obtained. The second problem considered in this research was to apply the adjoint-free methods to production optimization of the reservoir operating under special conditions that required coupling of two simulators and for which the adjoint code is not available. The model-reduced method could not be applied because of a low accuracy of the simulation solution which in case of long time simulations resulted in large approximation errors. Therefore, simultaneous perturbation stochastic algorithm (SPSA) was applied together with the finite difference gradient-based method to solve the production optimization problem. SPSA is a gradient-based method where the gradients are approximated by random perturbations of all controls in once, while the finite difference method approximates the gradients by perturbation of each control separately. Both approaches were very simple to implement, they resulted in the improvement of the production, but they were computationally relatively expensive.Applied mathematicsElectrical Engineering, Mathematics and Computer Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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