Browsing by Author "Vargas, Francisco M."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Prediction of the Phase Behavior and Properties of Hydrocarbons with a One-Parameter PC-SAFT Approach Assisted by a Group Contribution Method
    (2017-08-10) Feijo Evangelista, Renato; Vargas, Francisco M.
    Modeling thermodynamic properties can be challenging when the data available for parameters identification is limited. Fully-predictive group contribution (GC) methods have been developed as an alternative to overcome data scarcity. Although providing a higher degree of accuracy, most recent GC approaches require detailed information of the molecular structure, which is not acquirable for systems with unspecified components. This work intends to establish the foundation to address this specific scenario. The proposed PC-SAFT approach assisted by a homosegmented group contribution scheme permits parameters calculation with accuracy due to one adjustable parameter without requiring meticulous information regarding the molecular structure, for instance, the relative position between carbon-centered groups. This semi-predictive approach is especially suitable for cases in which some data is often available, but cannot be taken into consideration by current GC models. Sensitivity analyses indicated good predictability in the extreme case where a single vapor pressure data point is provided to adjust the model parameter, whereas enhanced predictions may be achieved if more data are available. This original modeling approach was further enhanced by redefining the groups based on carbon-13 nuclear magnetic resonance (13C-NMR). In this version, the groups are defined by spectrum segments delimited by specified boundaries, while the relative amount of groups in a molecule is quantified as the relative intensity of signals comprised within each specified range. Therefore, the 13C-NMR analysis of the fluid of interest may suffice as the sole source for the required structural information. The model parameter is fitted to at least one vapor pressure data point, which can be estimated using refractive index and molecular weight data, through a series of newly defined correlations. This approach is especially useful for cases where saturation pressure measurements are not practical, but refractive index is more easily quantified. Furthermore, these correlations represent an alternative method for calculating critical properties and acentric factor of non-polar hydrocarbons, as a function of molecular weight and refractive index, which has numerous potential applications. The concepts established in this work have shown promising potential for some industrial applications given the simplified experimental and computational implementation. For instance, equations of state have been extensively used to predict the phased behavior of petroleum fluids in the oil and gas industry, however obtaining the model parameters for these systems is still a challenge given that they often consist of undefined components. Therefore, the application of the concepts presented in this work is especially valuable in this scenario. In this context, a methodology for applying the approach to the modeling of petroleum fluids and in a fully-predictive manner was proposed and exemplified over hydrocarbon mixtures. With this work, I aim to motivate further evaluation of the proposed methodology for application to actual petroleum fluids and to inspire the development of practical methods to perform thermodynamic calculations of complex multicomponent mixtures.
  • Thumbnail Image
    Item
    Simultaneous Determination of Asphaltene Deposition and Corrosion under Dynamic Conditions
    (2018-11-27) Kuang, Jun; Vargas, Francisco M.
    Asphaltene deposition is one of the major flow assurance problems that could plug the production tubing, significantly impeding oilfield productivity. Conventional asphaltene dispersants are supposedly used to improve the stability of oils, thereby preventing asphaltene deposition. Currently, the injection of asphaltene dispersants has shown mixed results in the field. In this work, a multi-section packed bed deposition apparatus, which is designed to not only directly quantify the deposited asphaltenes but also investigate the deposition profile, is used to assess the performance of asphaltene dispersants at ambient conditions. Results indicate that the dispersive performance of the inhibitors is not directly related to their ability to prevent asphaltene deposition. In some cases, the chemicals with the highest dispersive efficiency produce the largest amount of asphaltene deposition. To determine asphaltene deposition under realistic production conditions, the development of a novel stainless-steel packed bed column deposition system is presented. The new design allows the feasibility of investigating a variety of factors affecting the deposition process under a wide range of temperature (20 – 300 ℃) and gauge pressure (0 – 3,000 psi). The impacts of operating temperature, type of precipitant, degree of asphaltene stability, and chemical additives on the deposition tendency of asphaltenes are discussed. Upon formation of the deposits, solvent wash is commonly used to re-dissolve the deposited asphaltenes in the well. In this work, a re-dissolution test apparatus using the packed bed column is introduced to evaluate solvents for in-situ asphaltene deposition remediation at high temperature and under dynamic conditions. Results suggest that screening of chemical solvents based on their solubility parameters may not provide an accurate indication of the selection of solvents. Furthermore, the effects of aging time, occluded oil, soaking temperature, and soaking time are investigated on the re-dissolution of asphaltene deposition. Besides asphaltene deposition, corrosion is a coexisting problem in the production tubing. Asphaltene inhibitors and corrosion inhibitors are usually injected into the well to solve the corresponding problem. In this dissertation, an integrated approach containing the critical micelle concentration measurements, the rotating cylinder electrode tests, and the packed bed column experiments is developed to evaluate the compatibility of the selected asphaltene inhibitor and corrosion inhibitor for oilfield applications. Results reveal that the corrosion inhibitor not only provides effective corrosion prevention, but also acts to mitigate asphaltene deposition. On the other hand, the asphaltene inhibitor fails to reduce deposition. It interacts and weakens the performance of the corrosion inhibitor injected simultaneously. The current research work introduces a new technology to not only determine the asphaltene deposition and corrosion tendencies on the metallic surfaces, but also assess the performance of asphaltene inhibitors and solvents for field applications. It will contribute to the development of advanced simulation tools to predict asphaltene deposition under realistic production conditions and cost-effective approaches to mitigate asphaltene deposition and corrosion simultaneously.