Kyeongseok Oh

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

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Publications (12)11.57 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.
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    ABSTRACT: When a waxy oil/water emulsion exits a wellhead and enters a deep undersea pipeline in the Gulf of Mexico, formation of methane hydrates and precipitated wax is likely due to the high pressure and cold temperature of the surrounding sea water. If this should occur, then wax will deposit on the pipeline walls and increase corrosion, whereas hydrates have the potential to plug the pipeline and completely block the flow. In the past, these problems have been avoided by insulating the pipelines, but this approach is becoming increasingly uneconomical as the need increases for longer pipelines. In this talk, we review a new strategy called "cold flow" in which the oil exiting the wellhead is transformed into a cold slurry with controlled particle morphology before entering the pipeline.
    2009 AIChE Annual Meeting; 11/2009
  • 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 03/2009; 23(3). · 2.85 Impact Factor
  • 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: Waxy components in a crude oil start to precipitate when the surrounding temperature is lower than wax appearance temperature (WAT). While the wax deposition can be initiated during the flow, wax gel formation occurs primarily under static conditions. When the wax gel develops within a relatively short time, certain pressure is needed to overcome the yield strength of the gel along the pipeline for restart. It was found that paraffinic components contribute to the evolving gel strength continuously while the oil is cooled below pour point (PP). Gel strength depends on wax amount and wax composition in the gel network. It has been reported that the gel properties depend on various factors: temperature, cooling rate, cooling time, shear history, and a diverse combination of factors. This study explores gel strength by stress exertion below the PP followed by further cooling. Model oil used in this study was prepared by mixing mineral oil and well-characterized wax. The measurements of WAT and PP were performed using the ASTM methods. A controlled-stress rheometer equipped with a cone-and-plate geometry and a Peltier plate device was employed to determine the yield stress and the measurement of creep response. The cooling was scheduled after applying stresses in the creep range. Yield behavior was compared after applying varying stresses and cooling to lower temperatures.
    11/2008;
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    ABSTRACT: High molecular weight paraffinic components have been attributed to impede the oil flow along the pipeline transport in low temperature environ by either wax deposition or wax gel formation. Wax deposition occurs even during the flow, while wax gel forms during the planned or emergency shutdown within a short period of time. It has been found that paraffinic components contribute to the evolving gel strength continuously while cooling below pour point. The contributive effect of asphaltenes to the yield stress of the gel formed was also studied. Model oils were used to determine the yield stress development in this study. Model oils were prepared by mixing mineral oil and kerosene with different amount of well-characterized waxes. The measurements of WAT and PP were performed using FT-IR and ASTM methods. As the WAT and PP are dependent on wax amount and wax quality, this study examined the WAT and PP by comparing model oils with different wax composition as well as different wax amount. Vane method was adapted to measure the yield stress at different temperatures. Constant cooling rate and consistent holding time were employed for the yield stress. The yield stress was recorded with decreasing temperatures. It was shown that the yield stress is strongly dependent on the wax amount and wax composition. Increase in yield stress values with decreasing temperature was greater for higher amount of wax in model oil indicating the gel strength is dependent upon the wax amount in the model oil. The x-intercept values obtained from yield stress versus temperature were interpreted as no-flow point, which may use as pour point alternatives. The relation between wax amount and yield stress was analyzed using FT-IR. Asphaltene used in this study is from Rangely field in northwestern Colorado. Examination of asphaltene addition was performed with 0.01 wt. % and 0.1 wt. % in model oil. Model oils were prepared with mineral oil, waxes, toluene, and asphaltene for this effort. Yield stress increases linearly decrease in temperature in asphaltene-free model oil. Asphaltene additions result in pour point reductions, 1 C in 0.01 wt%, and 4 C in 0.1 wt%. Small amount of asphaltene (0.01 wt. %) also played a significant role in yield stress reduction. A considerable reduction in yield stress was observed by asphaltene addition. A departure form the linear trend in increase of yield stress with decreasing temperature was observed at lower temperatures in the model oils with asphaltenes.
    2008 AIChE Spring National Meeting; 04/2008
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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
  • 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 04/2002; 16(3). · 2.85 Impact Factor