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  • 1
    Electronic Resource
    Electronic Resource
    On position-space renormalization group approach to percolation (1995)
    Springer
    Journal of statistical physics 78 (1995), S. 1157-1164 
    Details
    ISSN: 1572-9613
    Keywords: Percolation ; renormalization ; universality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a position-space renormalization group (PSRG) approach to percolation one calculates the probabilityR(p,b) that a finite lattice of linear sizeb percolates, wherep is the occupation probability of a site or bond. A sequence of percolation thresholdsp c (b) is then estimated fromR(p c ,b)=p c (b) and extrapolated to the limitb→∞ to obtainp c =p c (∞). Recently, it was shown that for a certain spanning rule and boundary condition,R(p c ,∞)=R c is universal, and sincep c is not universal, the validity of PSRG approaches was questioned. We suggest that the equationR(p c ,b)=α, where α isany number in (0,1), provides a sequence ofp c (b)'s thatalways converges top c asb→∞. Thus, there is anenvelope from any point inside of which one can converge top c . However, the convergence is optimal if α=R c . By calculating the fractal dimension of the sample-spanning cluster atp c , we show that the same is true aboutany critical exponent of percolation that is calculated by a PSRG method. Thus PSRG methods are still a useful tool for investigating percolation properties of disordered systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02183708
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  • 2
    Electronic Resource
    Electronic Resource
    The Effect of Asphalt Precipitation on Flow Behavior and Production of a Fractured Carbonate Oil Reservoir During Gas Injection (2000)
    Springer
    Transport in porous media 41 (2000), S. 325-347 
    Details
    ISSN: 1573-1634
    Keywords: fractured reservoir ; permeability ; injectivity index ; asphalt precipitation ; computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The first field data, collected over an 11 year period, are presented which indicate the possible effect of asphalt precipitation on the permeability and injectivity index of a fractured carbonate oil reservoir. The asphalt aggregates were formed during enhanced oil recovery by injection of a rich gas into the reservoir. The data indicate that, while at the initial stages of the operations the permeability and injectivity index decrease, at later times they appear to oscillate with the process time, with apparent oscillations' periods that depend on the heterogeneity of the reservoir. Two classes of plausible mechanisms that give rise to such oscillatory behavior are discussed. One relies on the changes in the structure of the reservoir's fractures, while the other one is based on asphalt precipitation in the reservoir. Computer simulations of flow and precipitation of asphalt aggregates in a pore network model of the reservoir are carried out. The results appear to support our proposition that asphalt formation and precipitation in the reservoir are the main mechanism for the observed behavior of the injectivity index. We also develop a stochastic continuum model that accurately predicts the time-dependence of the reservoir's permeability and injectivity index during the gas injection process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006759524127
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  • 3
    Electronic Resource
    Electronic Resource
    Asphalt flocculation and deposition: I. The onset of precipitation (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 10-22 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Formation of asphalt aggregates and their deposition on the pore surfaces of a porous medium, which alter the structure of the medium and its effective properties, is a critical problem to catalytic and oil recovery and refinery processes. Extensive new experimental data for the amount of precipitated asphalt formed with crude oil and various solvents are presented. Results indicate that, contrary to the previous assumptions, asphalt formation is at best partially reversible. A thermodynamic model based on the Flory-Huggins theory of polymer solutions is used, together with the Soave equation of state, to predict the data. Critical evaluation of the model shows that its predictions do not agree well with our data. As an alternative, we propose a new model that employs a scaling equation, somewhat similar to those encountered in aggregation and gelation phenomena. The scaling function takes on a very simple form, and its predictions are in very good agreement with the data. It also predicts that the onset of precipitation may obey a simple universal equation.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690420104
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  • 4
    Electronic Resource
    Electronic Resource
    Asphalt flocculation and deposition: II. Formation and growth of fractal aggregates (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 3318-3332 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Extensive small-angle X-ray and neutron-scattering data, as well as results of precipitation measurements, are analyzed to delineate the structure of the asphalt and asphaltene aggregates that are formed when a solvent is injected into a system containing crude oil. The two types of data strongly suggest that both small and large aggregates have a fractal structure, with well-defined fractal dimensions. If the system is aged long enough at low enough temperature, large asphalt particles will have the structure of diffusion-limited cluster-cluster aggregates with a fractal dimension Df ≃ 1.8, while the small ones are similar to diffusion-limited particle aggregates with a fractal dimension df ≃ 2.5. High temperatures increase the rotational motion of the particles, disturb the structure and mechanical stability of the aggregates, and decrease their fractal dimension. Aging and concentration effects of the asphalts in the solution, and the type of the solvent on the structure of the aggregates are also investigated. Implications of these results for the structure, mechanical stability, and molecular-weight distribution of asphalts and asphaltenes are detailed. A new molecular-weight distribution for asphalt aggregates predicts the experimental data excellently.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690421204
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    Paper (German National Licenses)
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