Browsing by Author "Vargas, Francisco M"

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    Asphaltene Behavior in Crude Oil Systems
    (2013-10-31) Panuganti, Sai; Chapman, Walter G.; Vargas, Francisco M; Hirasaki, George J.; Tomson, Mason B.
    Asphaltene, the heaviest and most polarizable fraction of crude oil, has a potential to precipitate, deposit and plug pipelines, causing considerable production costs. The main objective of this study is to contribute to the thermodynamic and transport modeling of asphaltene in order to predict its precipitation, segregation and deposition. Potential calculation of some thermophysical properties of asphaltene is also explored. Predicting the flow assurance issues caused by asphaltene requires the ability to model the phase behavior of asphaltene as a function of pressure, temperature and composition. It has been previously demonstrated that the Perturbed Chain form of Statistical Association Fluid Theory (PC-SAFT) equation of state can accurately predict the phase behavior of high molecular weight compounds including that of asphaltene. Thus, a PC-SAFT crude oil characterization methodology is proposed to examine the asphaltene phase behavior under different operating conditions. With the fluid being well characterized at a particular reservoir depth, a compositional grading algorithm can be used to analyze the compositional grading related to asphaltene using PC-SAFT equation of state. The asphaltene compositional grading that can lead in some cases to the formation of a tar mat is studied using the same thermodynamic model. Quartz crystal microbalance experiments are performed to study the depositional tendency of asphaltene in different depositing environments. The possibility of simulating asphaltene deposition in a well bore is discussed by modeling the capillary data, which simultaneously accounts for asphaltene precipitation, aggregation and deposition. The work presented is expected to contribute to the calculation of thermophysical properties of hydrocarbons and in particular of asphaltene, characterization of crude oils, improve tools to model asphaltene phase behavior, check the quality of fluid samples collected and the accuracy of (pressure, volume and temperature) PVT tests, reduce the uncertainties related to reservoir compartmentalization, optimize the logging during data acquisition, prediction of tar mat occurrence depths, improved understanding of the asphaltene deposition process, and finally optimize the wellbore operating conditions to reduce the asphaltene deposit.
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    Mechanistic Investigation and Modeling of Asphaltene Deposition
    (2019-04-19) Rajan Babu, Narmadha; Vargas, Francisco M
    The potential for asphaltene to get precipitated and deposited in wellbore and flowlines under changes in pressure, temperature, and composition of crude oil is a major concern for the oil and gas industry. In this work, an integrated approach to model asphaltene precipitation, aggregation, and deposition on a single platform is presented. It focuses on the development of a deposition simulator that performs thermodynamic modeling using the Perturbed Chain version of the Statistical Associating Fluid Theory Equation of State (PC-SAFT EOS) and depicts the deposition profile by means of a Computational Fluid Dynamics (CFD) model based on Finite Element Method (FEM). The developed deposition model for predicting asphaltene deposition in wellbore and pipelines consists of three parameters, one each for precipitation, aggregation, and deposition. The precipitation and aggregation kinetic parameters are calibrated with respect to an NIR spectroscopy experimental technique and the deposition kinetic parameter is calibrated with respect to packed bed column deposition tests. The model not only helps in simulating asphaltene deposition in a packed bed column, but it is also extended to simulate asphaltene deposition in RealView, a wide-gap Couette-Taylor device. The effect of chemical dosage on asphaltene deposition is investigated with the help of a modified version of the developed model, which helps in assessing the inhibitive and dispersive tendencies of the chemicals used to mitigate or remediate asphaltene deposition. The calibrated model parameters are studied as a function temperature and driving force towards precipitation and deposition, and scaling functions are established to scale the parameters from the laboratory-scale to real field conditions. Simulations are performed with the help of the developed asphaltene deposition simulator and the model captures the behavior of asphaltene deposited along the length of the wellbore, for deepwater oil reservoir under gas injection. Simulation methods for oil flow and asphaltene precipitation in the near-wellbore region of the reservoir and inside the production tubing are coupled to provide a comprehensive and wholesome understanding of this complex flow assurance problem. This work contributes to the development of a proficient simulator that can predict asphaltene deposition in both laboratory scale experiments and production tubings.
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    Thermodynamic Modeling of Hydrocarbon Mixtures with Application to Polymer Phase Behavior and Asphaltene Precipitation
    (2018-08-23) Sisco, Caleb; Vargas, Francisco M
    A new equation of state framework is proposed that hybridizes the classical cubic equations of state (EOS) with the chain term of the SAFT EOS. This model offers an improved description of the molecular features of long-chain molecules, such as heavy n-alkanes and polymers, whose thermodynamic properties are often poorly described by standard cubic EOS models. This hybrid EOS, called the cubic-plus-chain (CPC) equation of state, shows promising results for the n-alkanes and polymers studied and could ultimately be used for improving predictions for solvent-polymer phase splitting and asphaltene precipitation. Additionally, critical property correlations for nonpolar components proposed in a recent work are tested for their application to mixed solvent phase behavior modeling. Because the standard cubic EOS and CPC models require critical properties as inputs, the proposed correlations provide a means to calculate thermodynamic properties for mixed solvents given information on only molecular weight and refractive index – measurements that are simple to perform for both pure substances and mixtures – and have potential application to crude oil systems for which composition is unknown. Phase behavior modeling studies with the mixed solvent approach and cubic EOS show exceedingly good agreement to standard modeling approaches that require a detailed compositional analysis. Also, an asphaltic crude oil phase behavior study with a high GOR and asphaltene-rich fluid produced from a deep-water environment is presented. Thermodynamic modeling with PC-SAFT revealed interesting trends with respect to the properties of the bulk and onset phases that suggest that, though asphaltenes may be unstable in the bulk fluid, phase-splitting that is classically viewed as a precursor to deposition might sometimes produce two liquids of relatively low density whose compositions are much leaner in asphaltenes than phases commonly associated with deposition problems. As part of this study, a new algorithm for calculating saturation pressures of asphaltic crude oils is presented. This algorithm uses reliable methods to generate excellent trial phase compositions for initializing the upper and lower asphaltene onset and bubble pressure calculations.
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    Thermophysical Properties and Solution Thermodynamics of Hydrocarbon Systems at High Tempeartures and Pressures
    (2017-08-10) Wang, Fei; Vargas, Francisco M
    Hydrocarbon liquids and solutions are widely used in industry to produce different chemical products. Their thermophysical properties and phase behavior are important for enhancing production, improving operational efficiency and also increasing environmental sustainability. Easier, faster and more accurate approaches for property evaluations and solubility behavior predictions are in need, especially for complex hydrocarbon systems under extreme conditions, to which current methods may not be successfully applied. The solubility parameter is an inherent property of a material and also a key input parameter in solution models. Accurate evaluations of solubility parameters at high temperatures and pressures are not feasible by the conventional methods. Current correlations between solubility parameters and other properties are limited to ambient condition. The pressure effect on solubility parameter is usually ignored in previous research work. A novel approach to calculate solubility parameters using volumetric properties is proposed in this work. The temperature and pressure dependence equations of solubility parameter are derived based on fundamental thermodynamic relations. The proposed equations are applied to various hydrocarbon systems with great accuracy. The composition effects on solubility parameter of mixtures are also investigated for mixtures consisting of components different in shapes and sizes, for which the regular solution theory provides unsatisfactory predictions. A binary constant is introduced in this work, with which the solubility parameter of the mixture and excess Gibbs energy can be more accurately predicted. Easier and faster method to evaluate volumetric properties using optical property, refractive index, is proposed in this work. The correlations between thermal expansivity and isothermal compressibility with refractive index are developed based on Lorenz-Lorentz equation and a saturation density correlation. The new approach allows volumetric property evaluations using only refractive index measurements for pure hydrocarbons, their mixtures, and crude oils, which significantly reduces the complexity of experiments. Applications to crude oil systems are also provided to predict asphaltene precipitation and deposition tendency using refractive index measurements. The work presented in this dissertation aims to stimulate new approaches to correlate different thermophysical properties of non-polar hydrocarbons to optical properties, such as refractive index. A variety of advantages of using the proposed approach over the conventional density-based method have been discussed, including but not limited to easier and faster experimental procedure, significantly less sample required and less fouling problems.
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    Viscosity Modeling of Complex Fluids
    (2018-11-12) Zhang, Jieyi; Vargas, Francisco M
    Viscosity is an important fluid property that is widely used in many scientific and engineering disciplines. The viscosity of different substances and mixtures can vary orders of magnitude because of factors that affect the intermolecular interactions, such as the non-ideality of mixtures due to molecular size and shape differences, the physiochemical properties of its constituents, and its temperature and pressure. Since the intermolecular interactions can vary significantly from one fluid to another, the viscosity modeling and prediction procedure needs to be studied on a fluid-specific basis. The interplay of these factors makes predicting the viscosity of fluids difficult. Despite decades of research in this area, accurate prediction of viscosity for a wide range of substances and mixtures remains a challenge. The work presented here investigated four aspects of the viscosity modeling of complex fluids that covers reservoir fluids, nonpolar hydrocarbons, and aqueous glycols. Existing methodologies were evaluated and expanded for nonpolar hydrocarbon mixtures with applications in modeling reservoir fluids, which contributes to the understanding of the combined effect of characterization, equation of state, and viscosity models on the accuracy. In addition, a methodology based on simple optical or volumetric measurement at typical laboratory environment was developed for predicting the viscosity of pure and mixture of nonpolar hydrocarbon that are advantageous in areas such as cost and logistics. Furthermore, existing methodologies were assessed and extended for aqueous glycols mixtures, which revealed their capabilities and the limitations. Finally, a methodology was developed for accurate prediction of aqueous glycol systems with terminal hydroxyl groups based on the observed universal behavior, offering a unique approach to modeling the complex behavior of such systems. The advances presented in this dissertation furthered the current understanding and expanded the available options for the viscosity modeling of complex fluids, potentially enabling wide applications across industries.