1,720,965 research outputs found
Caprock integrity evaluation for geosequestration of CO2 in depleted petroleum reservoirs.
Get PDFThe geological storage of carbon dioxide (CO2), also referred to as CO2 geosequestration, represents one of the most promising options for reducing greenhouse gases in the atmosphere. However, sometimes CO2 is captured with small amounts of other industrial gases such as sulphur dioxide (SO2) and hydrogen sulphide (H2S), incurring extra costs to separate these other acid gases before the CO2 can be stored in depleted petroleum reservoirs or aquifers - or, it might be necessary to inject CO2 with a small amount of these gas impurities to save cost. Moreover, during CO2 geosequestration in reservoirs, pressure variations during injection and storage could force some amount of CO2 into the caprock, thereby altering the petrophysical and geochemical properties of the caprock. Also, CO2-brine-rock interactions during CO2 geosequestration can impact the brittleness of the formations due to changes in their mineralogical compositions during the geochemical reactions. Therefore, studies on the co-injection of CO2 with other acid gases from industrial emissions and their impact on caprock integrity are paramount. In this study, numerical simulations were performed using TOUGHREACT codes, to investigate the injection of pure CO2 and CO2 co-injection with SO2 or H2S into carbonate and sandstone formations, and their migration to shale caprock. Mineralogical brittleness models were derived from existing models, and one of the models that accounts for the relative level of brittleness of minerals was applied to evaluate the mineralogical brittleness index of the rocks. In addition, a machine learning approach to predicting the brittleness index of rocks was adopted and an artificial neural network (ANN) model was developed to evaluate the brittleness index of rocks using data from the numerical simulations of CO2 geosequestration in sandstone and carbonate reservoirs, overlain by shale caprock. The ANN model was developed using Python programming language. The findings of the study revealed that SO2 gas dissolves faster in brine compared to H2S gas when co-injected with CO2 gas in reservoir rocks. Thus, the region in the reservoir contacted by SO2 gas is smaller compared to H2S gas. SO2 gas dissolves more in sandstone reservoirs compared to carbonate reservoirs, due to the availability of more Fe-bearing minerals in the sandstone formation. The findings of the study also indicate that porosity and permeability increase for the CO2 alone and CO2-H2S injection cases, in both the carbonate and shale rocks; while for the CO2-SO2 injection case, porosity and permeability increase in the shale rock and carbonate rock (initially composed of calcite and dolomite) and decrease in the carbonate (pure and impure limestone) and sandstone rocks, due to anhydrite precipitation from the injection zone to the reservoir-caprock interface. During cyclic injection and withdrawal of CO2, for all the injection cases, the porosity and permeability of the sandstone reservoir decreased in a few layers directly below the perforation interval of the production zone. In all the sequestration cases and techniques, the brittleness of the shale and sandstone rocks decreases, while the change in the brittleness of the carbonate rocks varies depending on calcite precipitation or dissolution. The brittleness of the carbonate rock (initially made up of calcite and dolomite minerals) decreased only in a small region in the lower part of the reservoir. Therefore, carbonate reservoirs with similar mineralogy may be suitable for SO2 gas co-injection with CO2. Based on the mineralogical composition of the formations in this study, the injection of pure CO2 or CO2 co-injection with H2S or SO2 decreased the brittleness index of the clay-rich shale caprock slightly. The brittleness index of carbonate-rich shale caprock might increase during pure CO2 geosequestration. Therefore, a proper understanding of the mineralogical composition of formations before CO2 geosequestration is vital. The ANN model developed in this study predicted the brittleness index of rocks with R2 value greater than 99% and mean absolute percentage error (MAPE) of less than 0.7%. Hence, the ANN model predicts the brittleness index of the formations accurately
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
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
Geomechanically coupled modelling of fluid flow partitioning in fractured porous media.
Get PDFNaturally fractured reservoirs are characterised with complex hydro-mechanical dynamics. In these reservoirs, hydrocarbons can be stored and produced from the rock matrix, the fracture network, or both. Normally the fracture network is depleted much faster than the matrix blocks due to its increased hydraulic conductivity; consequently, the recovery factor is low for these reservoirs. Additionally, the in-situ stress profile changes with reservoir depletion and affects fluid flow dynamics of the fractured reservoir. Therefore, dynamic characterisation of fractured reservoirs is considered a challenging task, responsible for inefficient exploitation of their reserves. This dissertation focuses on characterising matrix-fracture fluid flow partitioning subjected to variable overburden stress loading. Understanding of the matrix-fracture hydro-mechanical interaction would assist in developing optimum production plans to maximize recovery from fractured reservoirs. Initially, three different fracture implementation techniques - (1) simulating fracture as an equivalent porous medium; (2) implementing it as a sub-dimensional feature within the porous matrix; and (3) considering fracture domain as an open channel - were evaluated using a set of published laboratory core flooding data. The best fracture simulation approach was identified to be fracture implementation as an open channel interacting with matrix block. This approach takes into consideration the coupling of Darcy flow equation in the matrix domain to Navier-Stokes flow formulation in the fracture. The efficiency of this fracture simulation approach was significantly enhanced when coupled further with poro-elasticity physics and stress dependent permeability. In the next step, the coupled open channel fracture simulation approach was applied to perform a sensitivity analysis on the effect of all parameters of the governing equations on fracture and matrix flow. The results of this analysis were statistically analysed, with specific attention to the analytical formulation of the governing equations, to develop coupled empirical flow models for fracture and matrix. These empirical models incorporate both flow physics of matrix and fracture, as well as mechanical loading impacts. An analysed multiphase flow scenario demonstrated the compatibility of the coupled simulation approach with multiphase flow investigations in fractured porous media. A novel core flooding set-up, capable of separated fracture and matrix flow measurement, was designed and built to enable laboratory evaluation of the developed empirical models. This set-up enabled monitoring of pressure front within matrix and fracture, taking the advantages of several differential pressure transducers along the core plug length. Variation of the matrix and fracture flow in response to different stress loading scenarios was investigated in the laboratory. Furthermore, laboratory validation indicated that the matrix flow model is capable of predicting laboratory measurements with an acceptable accuracy; however, the fracture flow model seemed to need more improvement. Probable factors that could have caused inaccuracy in the fracture flow model were discussed and actions for improving it were recommended as an extension to this research. Application of the empirical models in fractured porous medium characterisation simulations reduces the coupling-related numerical complexities. The coupled empirical models can predict flow dynamics of fractured reservoirs under various stress regimes. They demand much less computational effort and, as they incorporate geometrical factors, they can be up-scaled conveniently. In terms of production planning for fractured reservoirs, the empirical models can assist engineers to manage matrix and fracture production efficiently based on overburden stress variations
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
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
Neutron scattering study of stress-strain behaviour of porous geological materials. [Dataset]
No full textQuantifying the relationship between stress-strain and fracture is important to the perfection of fracture capability if it is to be used as a tool for guiding failure operations in geological materials drilling. The development of fracture prediction tools is critical for geological applications in oil and gas industry as the prospects for building understanding empirically will be limited due to the high costs associated with extreme condition field trials (e.g. North Sea). There are numerous data associated with porous geological material fracture investigations, but the value of this information is limited by an inability to accurately measure stress-strain within the sample. This work aims to use neutron techniques that can be interrogate the internal volume of porous crystalline geological specimens subjected to stress states at high temperature resembling geological conditions
- …
