BS and MS in Chemical Engineering Yonsei University, Seoul, Korea Researcher in the Samyang R&D Center, Taejon, Korea PhD in Chemical Engineering, University of Utah Research Scientist in the Petroleum Research Center and Utah Heavy Oil Center asphaltene@yahoo.com C.V. Ph.D. Thesis Abstract Ph.D. Thesis Abstract (Korean)

Research

Vane rheometer to measure the yield stress

Asphaltene effect on the wax gel formation: pour point and yield stress reduction

Released on September 2007

Transesterification Thermal process

Asphaltenes have been defined as solubility class materials, which are soluble in aromatics (toluene or xylene) and insoluble in low molecular weight alkanes (n-pentane or n-heptane). Onset of asphaltene precipitation has been used to determine asphaltene solubility. Onset is defined as a minimum amount of precipitant, such as pentane or heptane, needed to initiate asphaltene precipitation. Onset is determined using Near-IR spectroscopy. As a chemometric study, multivariate analyses such as partial least square (PLS) and principle component analysis (PCA) are carried out to examine asphaltene aggregation and self-aggregation behavior.

Career objectives

Conferences

1. Kyeongseok Oh, Kaushik Gandhi, Pankaj Tiwari and Milind Deo "Yield behavior of wax gel formation in the presence of Asphaltenes," AICHE Spring, New Orleans, LA, April 6-10, 2008.

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.

2. Oh,K.; Gandhi,K.; Magda, J.;Deo,M.D. “Characteristics of Wax Gels,” AICHE annual meeting, Salt Lake City, UT, Nov. 4-9, 2007.

Abstract
Wax gel formation during the planned and the emergency shutdown became one of the important research topics in the flow assurance. Wax appearance temperature (WAT) and pour point (PP) are oil characteristics to predict the wax plugging. Measurement and examination of WAT and PP have been well studied using various techniques. WAT and PP have been critical properties in evaluating the flow of crude oils in colder environs. However the temperature difference (DT) between WAT and PP has not been established in detail. It is the aim of this paper to investigate the differences in the two measurements for different model oil systems to gain an understanding of the mechanisms governing the transition from WAT to PP in a waxy oil. A series of model oils with known amounts of well-characterized paraffinic wax composition were used. Model oils were prepared by mixing mineral oil and kerosene with different amount of waxes. The measurements of WAT and PP were performed using DSC, FT-IR, NIR, rheometer 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. DT was observed to decrease with increasing the wax amount in model oils. Model oil with higher molecular weight of wax had higher values of DT. This indicates the mechanism differences in gel formation of waxes. In addition yield stresses were measured with rheometer using a vane method. Yield stresses were measured at different temperatures below PP for different model oils. Constant cooling rate and consistent holding time were employed for the yield stress measurements. It was shown that the yield stress is strongly dependent on the wax amount and wax composition. Vane method has a number of critical design variables, such as size of the enclosing chamber, temperature gradients in the chamber and cooling methods used. Yield stress values were observed to increase with decreasing measuring temperature in the examination range. 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.

3. Oh,K.; Magda, J.;Deo, M.D. “Yield stress measurements of wax gels,” The 8th International Conference on Petroleum Phase behavior and Fouling, Pau, France, June 10-14, 2007.

Abstract
Rheological models of oil gels and the measurements on which these models are based, are critical in establishing the restart performance of a gelled pipeline. In this paper, we report a comprehensive rheological study of waxy oils. A series of model oils with known amounts of well-characterized paraffinic wax composition were used in the first part of the study. Model oils were prepared by mixing a commercial wax sample, mineral oil and kerosene. A few waxy crude oils from the Uinta Basin with Wax Appearance Temperatures (WAT) of over 45 C were used in the second part of the study. Yield stresses were measured using conventional cone and plate viscometers and by employing a vane fixture. A constant-stress Rheometer was also used in both the cone and plate and vane arrangements. Yield stresses were measured at different cooling rates and holding times, and with and without the presence of a shearing environment. It was shown that the yield stress is strongly dependent on all of the above parameters and that care should be exercised in documenting the temperature and shear history of the oil for the formulation of accurate rheological models. It was also shown that care should also be exercised in using the cone and plate constant shear-rate method for yield stress measurements, when the shear stress extrapolation method is used. Vane method also has a number of critical design variables, such as size of the enclosing chamber, temperature gradients in the chamber and cooling methods used. The measurements were used to construct time-dependent yield stress (rheological) models, which can be used directly in restart calculations. One of the important features of the study was the investigation of the wax gel structure. Gel strength after gel breakage was measured by vane rotation by holding at the same temperature, and observed to be much lower than the original yield stress. Once the gel structure is broken, the gel network is not reformed and lower yield stresses are observed at all subsequently lower temperatures.