R-3 Repository :: Browsing by Author "Vargas, Francisco M."

Browsing by Author "Vargas, Francisco M."

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Advances in Thermodynamic Modeling of Nonpolar Hydrocarbons and Asphaltene Precipitation in Crude Oils
(2019-04-17) Abutaqiya, Mohammed I. L.; Vargas, Francisco M.
In this work, we present improved correlations to calculate PC-SAFT parameters for hydrocarbon components based on molecular weight and refractive index (or density) at 20 °C without prior knowledge of the hydrocarbon family. We use the correlations to develop a fully predictive approach for the modeling of the temperature- and pressure-dependence of density of crude oils and petroleum fractions (e.g. gasoline, diesel, and jet fuels). These hydrocarbon mixtures are treated as lumped-solvents and are modeled with PC-SAFT parameterized from simple laboratory measurements of molecular weight and refractive index (or density) at 20 °C without detailed knowledge of composition. The approach is also extended to the modeling of live oils under gas injection. The predictive capability of the model is tested against 591 density measurements and 116 bubble point measurements from 32 crude oils from around the world. The model can predict, without any tuning parameters, density and bubble pressure with an accuracy of 1.06% and 4.82%, respectively, for live oils and their gas blends. We also develop a hydrocarbon characterization factor based on molecular weight and refractive index. The new characterization factor, called the aromatic ring index (ARI), can clearly distinguish between different families of hydrocarbons and provide an indication of the number of aromatic rings in the component. ARI us used throughout this work as a measure of aromaticity. The developed correlations and ARI concept are implemented in a characterization procedure for modeling polydisperse asphaltenes from a crude oil produced in deep-water. We use probability distributions to represent the maltenes and asphaltenes which allows for the generation of any number of pseudo-components without the need of extra tuning parameters. We perform a sensitivity analysis to investigate the implications of treating asphaltenes as a mono- or a poly-disperse mixture. From the modeling results of the UAOP envelope for the deep-water oil, we observe that PC-SAFT predicts a minimum in the upper critical solution temperature (MUCST). We develop a semi-empirical model that accurately captures the low-temperature behavior of the LLE phase boundary. The model is based on a linear extrapolation of normalized cohesive energy (LENCE). Finally, in search for a better model than the widely-used classical cubic EOS, we conclude this research work by presenting a general formulation of the newly-developed cubic-plus-chain (CPC) equation of state which hybridizes the classical cubic EOS with the chain term from SAFT. The general formulation allows the use of any cubic EOS (e.g. vdW, SRK, PR,…etc.) as a reference with any radial distribution function (e.g. Carnahan-Starling, Elliott,…etc.) for the chain term. This formulation facilitates future research for the improvement of CPC EOS for the final purpose of modeling polymer and crude oil systems.
Characterizing Asphaltene Deposition in the Presence of Chemical Dispersants in Porous Media Micromodels
(American Chemical Society, 2017) Lin, Yu-Jiun; He, Peng; Tavakkoli, Mohammad; Mathew, Nevin Thunduvila; Fatt, Yap Yit; Chai, John C.; Goharzadeh, Afshin; Vargas, Francisco M.; Biswal, Sibani Lisa
Asphaltenes are components in crude oil known to deposit and interrupt flows in critical regions during oil production, such as the wellbore and transportation pipelines. Chemical dispersants are commonly used to disperse asphaltenes into smaller agglomerates or increase asphaltene stability in solution with the goal of preventing deposition. However, in many cases, these chemical dispersants fail in the field or even worsen the deposition problems in the wellbores. Further understanding of the mechanisms by which dispersants alter asphaltene deposition under dynamic flowing conditions is needed to better understand flow assurance problems. Here, we describe the use of porous media microfluidic devices to evaluate how chemical dispersants change asphaltene deposition. Four commercially used alkylphenol model chemical dispersants are tested with model oils flowing through porous media, and the resulting deposition kinetics are visualized at both the matrix scale and pore scale. Interestingly, initial asphaltene deposition worsens in the presence of the tested dispersants, but the mechanism by which plugging and permeability reduction in the porous media varies. The velocity profiles near the deposit are analyzed to further investigate how shear forces affect asphaltene deposition. The deposition tendency is also related to the intermolecular interactions governing the asphaltene–dispersant systems. Furthermore, the model system is extended to a real case. The use of porous media microfluidic devices offers a unique platform to develop and design effective chemical dispersants for flow assurance problems.
Examining Asphaltene Solubility on Deposition in Model Porous Media
(American Chemical Society, 2016) Lin, Yu-Jiun; He, Peng; Tavakkoli, Mohammad; Mathew, Nevin Thunduvila; Fatt, Yap Yit; Chai, John C.; Goharzadeh, Afshin; Vargas, Francisco M.; Biswal, Sibani Lisa
Asphaltenes are known to cause severe flow assurance problems in the near-wellbore region of oil reservoirs. Understanding the mechanism of asphaltene deposition in porous media is of great significance for the development of accurate numerical simulators and effective chemical remediation treatments. Here, we present a study of the dynamics of asphaltene deposition in porous media using microfluidic devices. A model oil containing 5 wt % dissolved asphaltenes was mixed with n-heptane, a known asphaltene precipitant, and flowed through a representative porous media microfluidic chip. Asphaltene deposition was recorded and analyzed as a function of solubility, which was directly correlated to particle size and Péclet number. In particular, pore-scale visualization and velocity profiles, as well as three stages of deposition, were identified and examined to determine the important convection–diffusion effects on deposition.
Experimental study of the effect of commercial dispersants on the precipitation, aggregation and deposition of asphaltenes
(2015-11-30) Melendez Alvarez, Ariana A; Vargas, Francisco M.; Biswal, Sibani L; Verduzco, Rafael; Wellington, Scott
Asphaltene precipitation and subsequent deposition is a potential flow assurance problem for the oil industry nowadays. Moreover, because oil production is moving to more difficult production environments – e.g. deeper waters – or is focusing on extracting residual oil using enhanced oil recovery techniques, the significant changes of pressure, temperature and/or composition can aggravate asphaltene deposition problems. One of the most common strategies to prevent or at least reduce asphaltene deposition is the utilization of chemical additives. However, there are still several unresolved challenges associated with the utilization of these chemicals: First, the experimental conditions and results obtained in the lab are not always consistent with field observations. Also, in some cases these chemical additives seem to worsen the deposition problem in the field. Therefore, there is a clear need to revisit the commercial techniques used to test the performance of asphaltene inhibitors and to provide a better interpretation of the results obtained. In this work, a technique based on NIR spectroscopy is presented to evaluate the performance of three commercial asphaltene dispersants. The results are also validated using a digital optical microscope. This technique is faster and more reproducible compared to available methods such as Asphaltene Dispersion Test (ADT) and Solid Detection System (SDS). Also, unlike the ADT test, the proposed method can evaluate the performance of the dispersants in a wide range of temperatures and compositions. The chemical additive dosage, aging time and temperature effect on asphaltene aggregation process are also discussed in this manuscript. A new system to study asphaltene deposition on metal surfaces that offers advantages over capillary systems was developed. This new apparatus is based on a column packed with carbon steel spheres. The current version of this device operates at ambient pressure and has potential for the fabrication of a high-pressure system in the near future. The work presented in this dissertation will contribute to a better understanding of the variables that affect the performance of asphaltene dispersants, and the true effect these chemicals have on the complex multi-step mechanism of asphaltene precipitation, aggregation and deposition.
Mechanistic Investigation of Fouling of Heat Exchangers Caused by Asphaltene Deposition in Oil Refineries
(2019-04-19) Al-Shamlan, Yousef Easa; Vargas, Francisco M.
Asphaltene precipitation and subsequent deposition is a growing problem for the oil and gas industry. The so-called “cholesterol of the oil” is the heaviest and the most polar fraction of the oil that is well-known to cause flow assurance problems in the near-wellbore region and production tubing. It is also responsible for water-in-oil emulsion stabilization and problems in surface facilities, such as catalyst poisoning and heat exchanger fouling. Extensive research has been conducted over the last few decades to better understand and predict the precipitation and deposition of asphaltenes in the wellbore. However, the knowledge and tools to forecast and mitigate the fouling caused by asphaltenes in downstream facilities are somewhat limited. Refineries all over the world suffer from this problem that has been declared inherent to the heating process itself, which causes a loss of approximately $ 5 million per year on average. In this work, I provide a comprehensive analysis of the general mechanisms by which asphaltenes precipitate and deposit and analyze the variables that govern this multi-step process. A comparison is made between the phase behavior of asphaltenes in upstream and downstream facilities. Moreover, a novel mechanism of inhibition for asphaltene deposition is proposed and validated experimentally. Furthermore, a modeling method has been adapted for the precipitation and deposition of asphaltenes at high temperatures based on the combination of the Perturbed Chain version of the Statistical Associating Fluid Theory Equation of State (PC-SAFT EOS) and a computational fluid dynamics (CFD) model. New insights into the effect of temperature on the asphaltene precipitation and deposition tendencies have been drawn from the experimental and the modeling work performed in this thesis. Unlike the well-known asphaltene precipitation phenomenon driven by pressure depletion in the wellbore, in the case of the heat exchangers, where the temperature is much higher, asphaltene precipitation and subsequent deposition is driven by a temperature gradient. It has been confirmed, that as the temperature increases above a certain range, the solubility of asphaltenes in oil decrease, resulting in a higher accumulation of asphaltene deposits on the tube surface. The simulation results are consistent with field observations. The proposed methods can enable both the manipulation of the process variables to minimize fouling in heat exchangers and the development of alternative methods that have the potential to remove asphaltenes and increase the temperature of the oil to the desired conditions. With this work, I aim to contribute to the understanding and ultimate solution to a long-standing problem that threatens the cost-effective production and refining of crude oils.
Utilization of Asphaltenes as Inexpensive and Abundant Precursors of Novel Carbon-Based Nanomaterials
(2019-08-07) Enayat, Shayan; Vargas, Francisco M.
Asphaltene deposition causes many difficulties and imposes challenging flow assurance problems for the oil industry throughout the globe. Asphaltenes are the heaviest and most polarizable fraction of crude oil. They have a high tendency to destabilize and deposit in the wellbore, oil reservoir formations, transportation pipelines, surface facilities, and heat exchangers. The significant difficulties associated with asphaltene deposition can cost oil companies millions of dollars each year. This problem will almost certainly become worse as the oil industry is moving towards production from deep-water reservoirs and implementation of the enhanced oil recovery by miscible gas injections. Despite the tremendous efforts and studies undertaken over the past decades, a full understanding of asphaltene behavior and its inherent physical and chemical characteristics has not been achieved. More importantly, the successful utilization of this problematic but high potential material has not been extensively explored. In this dissertation, a series of comprehensive experimental methods were presented to better understand and predict the occurrence and the scale of asphaltene deposition. As a part of these methods, a novel NIR spectroscopy technique was developed to accurately monitor the kinetics of asphaltene precipitation and aggregation in crude oil systems. The effects of different variables, such as temperature, the driving force towards precipitation, and the addition of commercial chemical dispersant were evaluated. Unlike currently available techniques, this new method is fast and simple: it requires less than 2 ml of sample for each measurement, with the capability of performing experiments at high temperatures. The amount of precipitated asphaltene can be easily estimated by using a newly developed method called “Absorbance Ratio”, in which the light transmittance values from the spectroscopy experiments are readily translated into precipitated asphaltene amounts. These simple and quick lab-scale experiments facilitate establishing modeling tools to scale the asphaltene precipitation and aggregation parameters to real-field, high-pressure, and high-temperature conditions. Furthermore, the potential production of carbon-based nanoparticles from asphaltenes was investigated in this work. To achieve this goal, first, a physical spray drying method was developed, in which fully dissolved asphaltene solutions were sprayed on a hot surface in order to evaporate the solvent quickly. Once the solvent evaporated, individual asphaltene nanoparticles with a high association tendency could be separated and deposited on the substrate. Scanning electron microscopy (SEM) results showed that asphaltene nanospheres as small as 20 nm in diameter were generated. The impact of different variables, such as temperature, type of the hot surface, and the asphaltene solution concentration on the size and morphology of the particles, were also discussed. Additionally, a new method of chemical oxidation by a concentrated nitric acid, followed by heat treatment was applied to asphaltenes. This oxidation reaction resulted in water-soluble and photoluminescent carbon-based nanoparticles. In this new method, the nitric acid used for oxidation could be recycled and reused as well. Moreover, the utilization of asphaltenes in two different areas of electrocatalysis and energy storage was pursued. To achieve these ideas, asphaltene samples were converted into nitrogen-doped graphene-like nanosheets (N-GNS) and highly porous activated carbons. These novel nanomaterials with exceptional properties, such as high surface area, good conductivity, high porosity, and ion mobility, were tested as catalysts for hydrogen evolution reactions and as electrodes for supercapacitors. The N-GNS sample, due to its high electrochemical active surface area (ECSA), presence of a mixture of porous structures, uniform layers, and effective doping of nitrogen atoms within the carbon matrix, was considered as an excellent candidate for the hydrogen evolution reaction (HER). The results illustrated a significant catalytic performance from the N-GNS sample when used as a catalyst in hydrogen evolution reactions. In addition, a novel method was developed to chemically transform asphaltenes into highly porous activated carbon with an interconnected honeycomb-like structure. The obtained activated carbon illustrated an impressive, ultra-high surface area of 3868 m2/g. The results of the study indicate that this new technique not only allowed a greater yield of asphaltene-derived activated porous carbon output as compared to the conventional activation method, but also created a mixture of microporous and mesoporous networks, which demonstrated favorable properties for supercapacitor applications. Finally, the hydrophobicity of asphaltenes was utilized in modifying commercially available melamine sponges to transform them into hydrophobic and oleophilic absorbent materials. The asphaltene-coated sponges showed excellent selectivity towards organic solvents and repelled water as soon as they came into contact with the liquids. In addition, the robust and flexible physical structure of sponges would enable them to be used multiple times. Overall, it was shown that the asphaltene-coated sponges, due to their impressive selectivity, high absorption capacity and good recyclability, could be promising candidates for large scale removal of oil spills and other organic liquids from water. Ultimately, the findings presented in this dissertation suggest that what is currently considered an undesirable fraction of crude oil, which has a tendency to deposit in wellbores, pipelines, and downstream facilities, can be repurposed into a desirable material with remarkable properties for nanoparticles fabrication, electrocatalysis, energy storage, oil spill removal, and other applications.

Browsing by Author "Vargas, Francisco M."

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