Browsing by Author "Vargas, Francisco"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Lattice-Boltzmann Modeling of Potential Fluid Flow Impairment Caused by Asphaltene Deposition in Porous Media
    (2018-11-30) Lin, Pei-Hsuan; Vargas, Francisco; Biswal, Sibani L.; Akin, John E.
    Asphaltene deposition in porous media has significant effects on oil flow during primary and secondary oil production. When asphaltenes deposit in porous media, the pore throats become plugged, leading to the impairment of permeability, and in turn causes several difficulties for oil production. In order to solve the problem of asphaltene deposition in porous media, it is important to understand the mechanism of asphaltene deposition in order to find measures to mitigate this problem. Moreover, a predictive model would greatly help control and reduce asphaltene deposition at the early stage. However, the mechanism of asphaltene deposition in porous media is still unclear. Only a few deposition models have been proposed and most of them have too many fitting parameters. Hence, the objective of this study is to propose a new model which has a fewer number of fitting parameters but still effectively predicts asphaltene deposition. Furthermore, the validity of the proposed model will be verified by microchannel and core flooding experiments. Instead of using the traditional Computational Fluid Dynamics (CFD) methods, such as the Finite Element Method, Finite Difference Method, and Finite Volume Method, the Lattice Boltzmann Method (LBM) is employed to model asphaltene deposition in porous media. The benefit of using LBM for simulating fluid flow in complex geometric settings is that it is comparatively easier for computational implementation and parallel computing due to being a meshless technique. Once the mechanism of asphaltene deposition in porous media has been understood clearly, mitigation methods can be then applied to prevent asphaltene deposition. Also, the simulation tool that is developed using LBM can help reduce the cost involved in experiments, which is extremely important in the petroleum industry.
  • Thumbnail Image
    Item
    Molecular Engineering of Efficient and Robust Organic Photovoltaics
    (2019-11-22) Hu, Zhiqi; Verduzco, Rafael; Vargas, Francisco
    Organic photovoltaics (OPVs) are appealing alternatives to conventional silicon based solar cells due to their advantages of low-cost, light weight, high flexibility and solution processability. Those properties are of great interest to researchers and make OPV possible candidates as future source of clean energy. However, the low power conversion efficiency and poor mechanical stability prevent the realization of OPV devices for industrial applications. In this thesis, we will demonstrate methods to address the challenges mentioned above. Through investigation of light sensitive polymer materials and optimization of processing conditions, we are able to obtain a better understanding in how OPV performance is related to charge transfer at polymer interface and fabricate OPV devices with improved mechanical stability under stretching/bending induced deformation. Future work will focus on mechanical analysis and molecular simulation of stabilized OPV films. This will allow a better understanding in stability improvement of OPV film on a microscale level. Finally, I wish this thesis can provide insight to those who are interested in the fabrication of OPVs for real world applications.
  • Thumbnail Image
    Item
    New Insights into the Mitigation of Asphaltene Deposition and the Utilization of Asphaltene Deposits
    (2019-07-26) Khaleel, Aisha; Vargas, Francisco
    Asphaltene deposition is an ongoing flow assurance problem in the oil and gas industry that is associated with huge economic loss. Different aspects to this problem which includes asphaltene stability, asphaltene deposition and asphaltene characterization has been studied over the past few decades. Despite the extensive research in this area, a reliable technique to mitigate this flow assurance problem has not been identified. In this work, we propose a novel chemical free mitigation technique to prevent asphaltene deposition. In the proposed technique, dead oil collected at the wellhead is recycled back into the wellbore to reduce asphaltene precipitation. The stabilization effect of the dead oil reinjection was verified by calculating the solubility parameter, the phase envelope and the amount of asphaltene precipitated using a thermodynamic model; Perturbed Chain - Statistical Associating Fluid Theory (PC-SAFT). A shift in the asphaltene onset pressure (AOP) curve and a reduction in the amount of asphaltene precipitated was observed for four light oils from the Middle East. Results have shown that asphaltene precipitation can be eliminated by the simple reinjection of dead oil. It is well known that asphaltenes are a polydisperse mixture of molecules with a broad distribution of sizes and molecular characteristics. However, for simplicity asphaltenes have been assumed to be a monodisperse mixture and their deposition tendency has been evaluated accordingly. In this work, we have performed a series of experiments to investigate the effect of asphaltenes polydispersity and aromaticity on their deposition tendency. We have compared asphaltene deposition for two model oils with the same total amount of asphaltenes but different asphaltene polydispersity distribution using a high pressure – high temperature packed bed deposition column. Although asphaltenes used in both oils were extracted from the same source, a drastic difference in the amount of asphaltene deposited was observed. Additionally, using UV-vis spectroscopy, we were able to show some similarity between aromaticity of asphaltene sub-fraction from different sources. This can be an indication that asphaltenes from different sources are not very different, and different behavior can be explained by the polydispersity of the asphaltene mixture. Asphaltene deposition problem is not limited only to upstream operations. Thus a number of researchers have studied the removal of asphaltenes through adsorption. Due to asphaltenes low value and limited applications, there was no research interest in retrieving the material. However, asphaltenes have a rich chemical structure and possess a semiconductor-type conductivity. In this work, we have investigated the utilization of asphaltenes as an active layer in organic photovoltaic (OPV) devices. A low power conversion efficiency was observed and this was justified by asphaltenes high association rate. Asphaltenes aggregates might add surface defects, which reduces the carrier mobility and thus the efficiency of the device. Thus, asphaltenes were chemically modified to reduce their tendency to aggregate. This was done by oxidizing asphaltenes in concentrated nitric acid and concentrated sulfuric acid, where the oxidation was thought to disaggregate asphaltenes nano-domains. The oxidation reaction resulted in a blue fluorescent quantum dots. The findings presented in this dissertation will help understand asphaltene deposition and the behavior of asphaltenes from different sources. This will allow a better understanding to the fundamentals behind asphaltene deposition and allow a better characterization of this poorly defined solubility class material. Additionally, this work contributes to adding value and the utilization of this waste by product from the oil and gas industry.
  • Thumbnail Image
    Item
    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.