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We present a two-dimensional model of the primary cementing process for foamed cement slurries. Foamed cement slurries have a number of claimed advantages, but also have a pressure-dependent density and rheology. The rheology is h...
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We present a two-dimensional model of the primary cementing process for foamed cement slurries. Foamed cement slurries have a number of claimed advantages, but also have a pressure-dependent density and rheology. The rheology is hard to quantify fully over all ranges of foam quality, which compromises the accuracy of models. The density variation is due to expansion/compression of the gas phase along the well, caused by variations in the static pressure. We show that in the absence of careful control, buoyancy-driven instabilities can result in the annulus, as the foamed slurry expands and the density drops below that of the displaced drilling mud. These instabilities appear to be of a classic porous media/Hele-Shaw cell fingering type, triggered by a threshold unstable density difference. We show that these instabilities are amplified by wellbore eccentricity, occurring lower in the well than in a concentric annulus. Our results question the safe usage of foamed cements in primary cementing.
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We present a new method to track the interface between two fluids in an annular displacement flow typical of setting surface casing in the primary cementing of oil and gas wells. The main idea is to exploit the density difference ...
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We present a new method to track the interface between two fluids in an annular displacement flow typical of setting surface casing in the primary cementing of oil and gas wells. The main idea is to exploit the density difference between successive fluids pumped in order to design a tracer particle to sit at the interface. Although apparently trivial, such particles must overcome viscous drag and strong secondary flows in order to reach and remain at the interface. We explore the underlying physics through both a simple toy model and using a full annular displacement simulation. The study provides a proof of concept that the method can work, but also exposes some limitations in terms of cementing parameters and particle properties. As well as demonstrating feasibility, we explore how some of these limitations might be overcome. Published by AIP Publishing.
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The rapidly growing number of people who find work via online labor platforms are not employees, nor do they necessarily fit traditional conceptualizations of independent contractors, freelancers, or the self-employed. The ambiguo...
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The rapidly growing number of people who find work via online labor platforms are not employees, nor do they necessarily fit traditional conceptualizations of independent contractors, freelancers, or the self-employed. The ambiguous nature of their employment status and its implications for worker well-being have attracted substantial controversy, but to date most empirical research in this area has focused on the market efficiency of a single platform rather than on workers themselves and related human resource management issues. Research progress will require understanding how online labor platform work differs from other types of nonstandard employment arrangements, as well as critical differences across labor platform firms in how work and workers are managed. This paper proposes a conceptual classification framework to facilitate research on the attitudes, experiences, and outcomes of workers who use these platforms. We explore how labor platform firms' operational choices shape how control is allocated across workers, clients, and the firm, and how they influence workers' autonomy, incentives, and degree of economic dependence on the firm. Implications for theory development, research, and managing worker-firm relations are discussed.
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This paper focusses on obtaining a better understanding of the subsurface geology of the Chibougamau area, in the northeast of the Abitibi greenstone belt (Superior craton), using geophysical data collected along a 128 km long tra...
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This paper focusses on obtaining a better understanding of the subsurface geology of the Chibougamau area, in the northeast of the Abitibi greenstone belt (Superior craton), using geophysical data collected along a 128 km long traverse with a rough southwest-northeast orientation. We have constructed two-dimensional (2D) models of the study area that are consistent with newly collected gravity data and high-resolution magnetic data sets. The initial models were constrained at depth by an interpretation of a new seismic section and at surface by the bedrock geology and known geometry of lithological units. The attributes of the model were constrained using petrophysical measurements so that the final model is compatible with all available geological and geophysical data. The potential-field data modelling resolved the geometry of plutons and magnetic bodies that are transparent on seismic sections. The new model is consistent with the known structural geology, such as open folding, and provides an improvement in estimating the size, shape, and depth of the Barlow and Chibougamau plutons. The Chibougamau pluton is known to be associated with Cu-Au magmatic-hydrothermal mineralisation and, as the volume and geometry of intrusive bodies is paramount to the exploration of such mineralisation, the modelling presented here provides a scientific foundation to exploration models focused on such mineralisation.
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There is a widely popular perception in the cementing community that the turbulent regime should be used where possible in primary cementing of oil and gas wells. We conduct a detailed numerical study and analyze turbulent annular...
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There is a widely popular perception in the cementing community that the turbulent regime should be used where possible in primary cementing of oil and gas wells. We conduct a detailed numerical study and analyze turbulent annular displacement flows. In particular, we show what roles viscous and buoyancy stresses play in the displacement efficiency. More importantly, we argue that the long-standing industry practice of preferring a turbulent displacement flow over laminar is over-simplistic and questionable. Indeed, we demonstrate that if the flow rate is increased very much when turbulent, steady displacements will be lost. Published by AIP Publishing.
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This study investigates political culture in the city of Tehran, focusing on three of its domains including typology of political culture, classification and typology of political citizens, as well as examination of some variables...
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This study investigates political culture in the city of Tehran, focusing on three of its domains including typology of political culture, classification and typology of political citizens, as well as examination of some variables affecting political culture in Iran. The applied research method is in the form of a survey and questionnaire-based data. The study sample size includes 612 citizens residing in Tehran in 2018. Findings show that most citizens are tended to a subject- parochial political culture. It is indicated that political variables i.e. the cost of political activity, government officials’ responsiveness, and institutional political trust are effective on political culture. Using cluster method, the citizens were divided into four categories: critical, obedient, unmotivated, and disappointed. Political culture factors are categorized in three groups by analyzing exploratory factors. These are: pluralistic, value, and involvement -behavioral. Findings show that, citizens have been grown higher in pluralistic, and with value aspects, but are in a low level with behavioral aspect, and this factor could be effective on political culture's type.
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We develop a simplified approach to predicting the displacement front behaviour of two Herschel-Bulkley fluids displacing one another along a narrow eccentric annulus in turbulent and mixed regimes. The approach involves the use o...
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We develop a simplified approach to predicting the displacement front behaviour of two Herschel-Bulkley fluids displacing one another along a narrow eccentric annulus in turbulent and mixed regimes. The approach involves the use of scaling arguments to reduce the full system of equations to a single hyperbolic equation that models the displacement front evolution. Analysis of the flux function is sufficient to predict whether or not the front will elongate along the annulus. Predictions of the simplified model are compared with a two-dimensional annular displacement model, showing good predictive abilities. The underlying eccentric annular flow is important in the industrial process of primary cementing. More specifically, the proposed method is aimed to provide a quick and reliable computational framework for analyzing primary cementing flows, leading to more successful cementing designs. (C) 2020 Elsevier Ltd. All rights reserved.
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In this paper, three types of concrete beam with two different lengths of encapsulated polyurethane adhesive were tested and the self-healing performance was measured by applying static torsion load. Based on the measured concrete...
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In this paper, three types of concrete beam with two different lengths of encapsulated polyurethane adhesive were tested and the self-healing performance was measured by applying static torsion load. Based on the measured concrete rupture resistance in torsion load it was shown that the cracks are filled by hydration products and the polyurethane is released by breaking the capsules. By comparing the use of self-healing concrete with reference beam, it is concluded that self-healing methods could compensate 80-95% of the total resistance of the reference beam. Finally, based on the contribution of FRP in torsion cracked beam, a code coefficient for each beams in restoration of a cracked concrete beam was suggested. (C) 2018 Elsevier Ltd. All rights reserved.
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