Browsing by Author "Rezaee, Sara"

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    Characterizing the Influence of Organic Carboxylic Acids and Inorganic Silica Impurities on the Surface Charge of Natural Carbonates Using an Extended Surface Complexation Model
    (American Chemical Society, 2019) Song, Jin; Rezaee, Sara; Zhang, Leilei; Zhang, Zhuqing; Puerto, Maura; Wani, Omar B.; Vargas, Francisco; Alhassan, Saeed; Biswal, Sibani L.; Hirasaki, George J.
    In this work, we developed an extended surface complexation model (SCM) that successfully fits all tested ζ-potential data (63 in total) of synthetic calcite and three natural carbonates (Iceland spar, Indiana limestone, “SME” rock from a Middle East field) in brines with divalent ions in a wide range of ionic strengths (0.001–0.5 M). To develop this extended model, our previous reported SCM is first optimized by incorporating the ζ-potential of synthetic calcite in a wide range of ionic strength (0.001–0.5 M) along with previously published data for parameter refitting. The model is then applied to predict the surface charge of synthetic calcite in concentrated solutions up to 5 M NaCl to reveal the role of high salinity in calcite wettability. Eventually, the model is extended to fit the ζ-potential of natural carbonates by adding surface reactions for impurities such as silica and organic-based carboxylic acids. The coverage of the organic impurities is found to be essential for explaining why the ζ-potential of natural carbonates is more negative compared to that of synthetic calcite. Naphthenic acid (assumed to have one carboxylic group) and humic/fulvic acid (assumed to have six carboxylic groups) are tested in the model calculation as possible sources of surface impurities to demonstrate the effect of the number of carboxylic groups in the acid molecule. Finally, the effect of a humic acid pretreatment on the ζ-potential of synthetic calcite is investigated experimentally to verify the assumption that absorbed organic impurities on the calcite surface contribute significantly to a more negatively charged natural carbonate surface when compared to that of pure calcite surfaces.
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    Separation and characterization of crude oils and investigation of their wetting properties on rock surfaces
    (2019-04-19) Rezaee, Sara; Vargas, Francisco
    The complexity of crude oil makes its compositional characterization a very challenging task. As a conventional method for characterizing crude oil, SARA fractionation is based on the differences between the solubility and polarity of the four fractions: Saturates, Aromatics, Resins, and Asphaltenes. Currently, some of the available methods for SARA separation are based on chromatographic principles that may possess some limitations, including requiring the solvent and sample in large amounts, being a time-consuming process, and providing irreproducible results. This study proposes two novel methods for maltene (SAR) and SARA analysis named the improved chromatographic technique and clay/alumina chromatography method respectively. We confirm that the new techniques require less solvent and that the amount of solvent for the desorption step does not depend on polar fractions content. Both methods are three to four times faster compared to the ASTM D2007 method. The proposed systems are practical for industrial application since the equipment is fairly inexpensive and can be easily assembled in any laboratory. Additionally, they do not require an expert operator to analyze the data, which is essential in some chromatography methods like High-Pressure Liquid Chromatography (HPLC). The improved chromatographic technique is only for maltene analysis, while this method makes it possible to collect the separated fractions and use them for further analysis. The clay/alumina chromatography method is for SARA analysis and does not require prior separation of asphaltene for maltene fractionation. As the most complex and heavy organic fraction of crude oil, asphaltenes are one of the major contributors flow assurance issues. It can significantly affect oil field production by depositing and blocking wells and flowlines. In this study, asphaltenes are fractionated into four parts based on their solubility in n-pentane, n-hexane, n-heptane, and n-octane. Asphaltene composition and structure are determined by elemental analysis and Fourier-transform infrared (FTIR) spectroscopy. Spectroscopy shows the functional groups in different asphaltene fractions (C5-6, C6-7, C7-8, C8+) to be the same. The aromaticity of C5-6 asphaltene is the lowest among the four fractions, however highest in C8+, which is the heaviest fraction, has the highest aromaticity. A new approach to aromaticity calculation is proposed based on elemental analysis, and the validity of the method is verified by comparing the results to aromaticity based on FTIR. Also, to investigate the polydispersity of asphaltene fractions, the molecular weight distribution is measured by gel permission chromatography (GPC). In the following part of the study, the effect of crude oil properties on wettability properties of calcium carbonate is studied. The tilting plate method was chosen as an appropriate method for contact angle measurement because it involves the formation of a rigid film instead of the use of the oil withdrawal method or a moving needle. The contact angle measurement method has some limitations; for instance, sometimes data is not reproducible. In this study, we propose a method of calcite preparation that involves controlling the brine layer on the surface calcite during the oil aging step. Additionally, the contact angle measurement procedure is simulated in a way designed to establish a wettability condition as close as possible to the reservoir condition. Moreover, the standard deviation of the method has been improved from 30° to 15°. We observe that the calcite tends to be more oil-wet when the water layer thins. In addition, this study also shows the importance of aging time in oil in the presence of brine and equilibration time of calcite in brine before contact angle measurement. It has been shown that low salinity NaCl brine alters the wettability from an oil-wet condition toward a more water-wet condition by contact angle measurement. Different approaches are presented in the literature to discuss the controlling mechanism of low-salinity brine flooding in improving oil recovery. In this part, we focus on crude oil compositions and properties including “water micro-dispersion formation,” “asphaltene stability,” “interfacial tension,” and their correlation with oil recovery by low-salinity brine flooding. We observe that increasing the water micro-dispersion formation leads to an increase in additional oil recovery, except for one crude oil which does not contain any asphaltenes. There is no direct correlation between the asphaltene onset of precipitation (vol. % heptane) and total oil recovery since as expected, not all of the asphaltenes are surface active. Additionally, we confirm that the most important and effective parameter is interfacial tension. It is correlated to the total /additional oil recovery with the highest R2 in comparison with the other parameters.