Kyeongseok Oh

University of Utah, Salt Lake City, UT, United States

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Publications (12)6.8 Total impact

  • Kyeongseok Oh, Milind D. Deo
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    ABSTRACT: Paraffinic waxes precipitate from bulk oil when oil temperatures are lower than the oil wax appearance temperature. The oil can form a gel if the temperature goes below the pour point, especially under quiescent conditions. The strength of the gelled waxy oil increases as temperature decreases further. Application of a mechanical shear deforms and fractures the gel. It is shown that this strength reduction in the gel is irreversible under isothermal conditions. In subsequent cooling, the prior fractured gel even showed much less yield stress than the gel from the shear-free condition at measured temperature. This study explored the gel strength behavior in water-in-oil (w/o) emulsion state. Three different model oils, water-free oil, 10wt.% w/o and 30wt.% w/o, were used to determine the yield stress using vane method. Both emulsified oils showed less yield stress values at temperatures between the pour points and ice temperature. Compared to water-free oil at temperatures below ice formation, the higher yield stresses were observed in 10wt.% w/o oil; however, the lower yield stresses in 30wt.% w/o oil. Subsequent cooling option after prior gel breakage was also examined.
    Fuel. 01/2011; 90(6):2113-2117.
  • K OH, P TIWARI, M DEO
    Oil Shale 01/2010; 27(3). · 0.64 Impact Factor
  • Kyeongseok Oh, Mark Jemmett, Milind Deo
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    ABSTRACT: Wax components in a crude oil start to precipitate when the surrounding temperature is lower than the wax appearance temperature. When wax gel develops under static conditions, a certain amount of pressure is needed to overcome the yield strength of the gelled oil in the pipeline for restart. It is shown that paraffinic components contribute to the evolving gel strength of the oil when cooled below the pour point. The gel strength was determined by the measurement of yield stress with and without subjecting the samples to creep stress. The existence of primary creep, secondary creep, and tertiary creep, was observed under isothermal conditions depending on the magnitude of the stress applied. This study explores the effect of prior creep stress with and without subsequent cooling of the samples. No significant degradation (reduction in yield stress) was observed after prior creep of the gelled oil at the same temperature. In the case of the subsequent cooling, applying prior creep stress application results in the dramatic increase of gel strength.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 09/2009;
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    ABSTRACT: When ambient temperatures are low, paraffinic crude oils being transported in pipelines may form gels composed of wax crystals. If pipeline flow ceases, these waxy gels may make it difficult to restart the flow without breaking the pipe. To predict the severity of this problem, we consider the rheology of a transparent model waxy crude oil for which pipeline flow visualization results are presented elsewhere. We investigate characteristics of the model oil determined by cone-plate shear flow measurements, such as the viscosity and wax appearance temperature, the gelation temperature, the elastic modulus, and the yielding behavior of the gel. The yielding behavior is a critical determinant of pipeline restart, and the time-dependent yielding behavior observed for this model oil is similar to that reported previously for North Sea crude oils. In particular, at sufficiently low-stress levels, the gel never yields, whereas the gel yields or “fractures” immediately at sufficiently high-stress levels. At intermediate-stress levels, the gel “creeps” with a delay time to fracture that ranges from seconds to hours, depending upon the imposed stress value. Some authors have suggested that waxy gels slowly degrade as they creep and that this gives rise to the very long delay times to fracture that may be observed. However, a creep-response hysteresis test on the model oil studied here shows that the gel elastic modulus does not vary with time during creep, a result which is inconsistent with the degradation mechanism.
    Energy & Fuels - ENERG FUEL. 03/2009; 23(3).
  • Kyeongseok Oh, Milind Deo
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    ABSTRACT: When pipelines are shutdown, waxy crude oils tend to form gels, which tend to plug the lines and stop flow. Restart requires sufficient pressure to overcome the yield stress of gelled oils. This study examines the yield strength of well-characterized waxy model oils at temperatures below the pour point. First, the yield stresses of model oils were determined by the vane method at different temperatures. Yield stress values were strongly dependent upon wax amounts and compositions, as expected. The extent of increase in yield stress values with temperature was greater for model oils that had a higher percentage of wax. The x-intercept values obtained from yield stress versus temperature were interpreted as no-flow points, which could be used as alternative measures of pour points. Second, the role of asphaltenes was examined in the evolution of the yield stress as the oil is cooled below the pour point. Asphaltene additions resulted in pour-point reductions, of up to 4 °C for additions of asphaltenes up to 0.1% (w/w). Small amounts of asphaltenes (0.01%, w/w) also played a significant role in yield stress reduction. The concept of steric hindrance and asphaltene aggregation was adapted to explain the yield stress reduction at the different asphaltene concentrations. At lower temperatures, as more wax came out of solution, the slope of the yield stress versus temperature line went back to the slope of the asphaltene-free oil, indicating the dominance of the wax networks at higher wax concentrations.
    Energy & Fuels - ENERG FUEL. 03/2009; 23(3).
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    ABSTRACT: Wax gel formation occurs in pipelines under quiescent conditions during a scheduled or emergency shutdown of flow. Paraffinic wax precipitates from the bulk oil when oil temperature decreases below the characteristic wax precipitation temperature, while the gelling begins as the temperature decreases below the pour point. Further temperature reductions below the pour point result in the development of a stronger gel. In this study, the gel strength was measured by determining the yield stress using the vane method. The method consisted of identifying the maximum torque exerted on the sample at various temperatures. Model oils were prepared by mixing low vacuum gas oil wax, mineral oil, and kerosene. Linear increase in gel strength with decreasing temperature was observed in the measured temperature range. As the wax content increased, so did the yield strength of the gel below the solution pour point. The slope of the yield-stress versus temperature line was also steeper for the model oil containing higher amount of wax. Recovery of gel strength was also examined by aging at the same temperature and by decreasing temperatures after breaking the gel at certain temperature.
    Petroleum Science and Technology 01/2009; 27(17):2063-2073. · 0.30 Impact Factor
  • Source
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    ABSTRACT: A parallel implementation of the three-dimensional Shan-and-Chen multicomponent, multiphase lattice Boltzmann method (LBM) was used to simulate the equilibrium distributions of two immiscible fluids in porous media. The simulations were successfully validated against cone-beam x-ray microtomographic data on the distribution of oil (decane), water, and air phases in a 5-mm cube of porous medium composed of packed quartz sand grains. The results confirm that LBM models allow for the straightforward incorporation of complex pore space geometry determined from x-ray microtomography measurements and that simulated wetting and nonwetting phase distributions are consistent with x-ray observations on both macroscopic and microscopic scales.
    Physical Review E 03/2008; 77(2 Pt 2):026710. · 2.31 Impact Factor
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    ABSTRACT: A parallel processing version of the 3D Shan-and-Chen (SC) multi-component, multiphase lattice Boltzmann method (LBM) was developed and used to simulate the distributions of two immiscible fluids in porous media. The model was tested for conformance to the laws of Laplace (fluid-fluid interfacial tension) and Young (contact angles). Then, the SC LBM was successfully validated against cone beam X-ray microtomographic data for the distribution of oil (decane), water, and air phases in a 5-mm cube of porous medium composed of packed quartz sand grains. The results confirm that LBM models allow for the straightforward incorporation of complex pore space geometry as defined from X-ray microtomography measurements and that simulated wetting and non-wetting phase distributions are consistent with X-ray observations on both macroscopic and microscopic scales.
    AGU Fall Meeting Abstracts. 12/2007;
  • Kyeongseok Oh, Milind D. Deo
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    ABSTRACT: Petroleum asphaltenes are extremely complex and are difficult to characterize. Asphaltenes are a solubility class, defined as that portion of the oil (or organic material) that is soluble in toluene and insoluble in normal heptane. (Sometimes, other alkane solvents are used to define this solubility class, the most common other solvent being, normal pentane.) Asphaltenes present numerous problems during production, transportation, and processing of crude oils because they are on the higher polarity and molecular weight end of the crude oil compositional spectrum. As a result, this solubility class has been widely studied. There are over a thousand papers on various aspects of asphaltenes, including their chemistry, molecular weight, solubility, phase behavior, reactivity, etc.1-4
    11/2007: pages 469-488;
  • Kyeongseok Oh, Terry A Ring, Milind D Deo
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    ABSTRACT: Asphaltenic solids formed in the Rangely field in the course of a carbon dioxide flood and heptane insolubles in the oil from the same field were used in this study. Four different solvents were used to dissolve the asphaltenes. Near-infrared (NIR) spectroscopy was used to determine the onset of asphaltene precipitation by heptane titration. When the onset values were plotted versus asphaltene concentrations, distinct break points (called critical aggregation concentrations (CAC) in this paper) were observed. CACs for the field asphaltenes dissolved in toluene, trichloroethylene, tetrahydrofuran, and pyridine occurred at concentrations of 3.0, 3.7, 5.0, and 8.2 g/l, respectively. CACs are observed at similar concentrations as critical micelle concentrations (CMC) for the asphaltenes in the solvents employed and can be interpreted to be the points at which rates of asphaltene aggregations change. CMC values of asphaltenes determined from surface tension measurements (in pyridine and TCE) were slightly higher than the CAC values measured by NIR onset measurements. The CAC for heptane-insoluble asphaltenes in toluene was 3.1 g/l. Thermal gravimetric analysis (TGA) and elemental compositions of the two asphaltenes showed that the H/C ratio of the heptane-insoluble asphaltenes was higher and molecular weight (measured by vapor pressure osmometry) was lower.
    Journal of Colloid and Interface Science 04/2004; 271(1):212-9. · 3.55 Impact Factor
  • Energy & Fuels - ENERG FUEL. 02/2003; 17(2).
  • Kyeongseok Oh, Milind D. Deo
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    ABSTRACT: Onset of solid precipitation from oils was determined by identifying the minimum in near-infrared absorbance. Solvent-induced precipitation typically causes asphaltene precipitation, but is also known to cause high-molecular-weight waxes to come out of solution. The effects of the addition of solid saturated and unsaturated compounds on the onset of solvent-induced precipitation from a crude oil were examined. Crude oil from Rangely, an oil field in northwestern Colorado was used. The solvent-induced precipitation was brought about using pentane, hexane, and heptane. On the basis of limited solvent carbon number investigated (5−7), less solvent was required for precipitation onset as the carbon number of alkanes decreased. As the flow rate of the precipitant increased, the onset was delayed. Addition of solid n-alkanes, such as eicosane and tetracosane to the oil initially, accelerated the onset of precipitation. When solid polyaromatic compounds (naphthalene and phenanthrene) were dissolved in the oil, more solvent was required to initiate onset of precipitation. It was also shown that the crude oil was considerably undersaturated with respect to the asphaltenes and that initial dissolution of asphaltenes in the oil accelerated the precipitation. The data provided insight on solubility-related solids precipitation from oils.
    Energy & Fuels - ENERG FUEL. 04/2002; 16(3).