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Dynamic Modeling and Experimental Study of Asphaltene Deposition in Wellbore Considering Mechanism of Precipitation, Aggregation and Deposition

Salehzadeh, Marziyeh | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55185 (06)
  4. University: Sharif University of Technolog
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ghotbi, Cyrus; Dabir, Bahram; Taghikhani, Vahid
  7. Abstract:
  8. Efforts to identify, predict, and resolve problems linked to asphaltenes and flow assurance have resulted in the development of numerous laboratory and modelling techniques. However, there has been little research on the molecular structure of asphaltenes and how it relates to solubility, stability, aggregation, and deposition behavior. Not only was a thorough structural analysis of asphaltene extracted from three samples of light, medium, and heavy oil performed in this study, but medium oil asphaltene was also fractionated into three sub-fractions based on solubility, with minimum, medium, and maximum solubility, and each subfraction was subjected to a structural analysis. All asphaltene samples were subjected to a variety of tests, including elemental analysis, EDX, mass spectrometry, FTIR, NMR, XRD, and SEM. Asphaltene aggregation and adsorption/deposition behaviors were also studied using DLS and EQCM devices. Following that, an integrated approach for modelling asphaltene precipitation and deposition in the wellbore was developed, in which the thermodynamic and asphaltene deposition modules were coupled to a multiphase flow simulator. In the thermodynamic module, the Peng-Robinson equation and the modified Miller-Flory-Huggins theory (based on asphaltene solubility) were used to compute the thermodynamic properties of oil and asphaltene precipitation, respectively. The deposition module was attached to the flow simulator to account for the effect of the asphaltene deposition layer on the fluid flow. It was based on mass conservation equations in the transport of asphaltenes. Because there were no field data for asphaltene deposition of light and medium oil, laboratory results could not be used in this section. However, field data from another light oil well that produced through tubing was used to validate the integrated model. The characterization section revealed that asphaltenes of heavy oil and most soluble sub-fraction had the highest hydrogen content and hydrogen to carbon atomic ratio, the lowest aromatics and olefinic components among other asphaltene samples. Furthermore, the alkyl side chains were longer and the mass-to-charge (m/z) distributions had broader spectrum. The trend of hydrogens in position mirrored the trend of heteroatom concentration, having higher average value observed in the most soluble sub-fraction and medium oil asphaltenes. According to the results in this section, the deposition and instability of asphaltenes are mostly due to stronger attractive - interactions and lower steric hindrance between their molecules. Hydrogens in α position followed the trend of heteroatom concentration, with greater average values found in the most soluble sub-fraction and medium oil asphaltenes. According to the data obtained in this part, the deposition and instability of asphaltenes was primarily attributed to the greater attractive π-π interactions, as well as reduced steric hindrance between their molecules. The data of asphaltenes aggregation and adsorption/deposition revealed that in light oil asphaltenes and the sub-fraction with the lowest solubility, the growth rate of particles and the propensity of adsorption/deposition of asphaltenes on the gold surface are higher than in other samples. It should be mentioned that the presence of high soluble sub-fractions in parent asphaltene (medium oil asphaltene) results in relatively higher stability and lessens the tendency to agglomeration, adsorption/deposition when compared to sub-fractions with lowest solubility or light oil asphaltene. In the modelling part, the integrated technique established in this work was in good agreement with the field data while greatly reducing calculation time. Further modelling studies revealed that assuming fixed pressure, temperature, and velocity profiles without taking into account the evolution of the asphaltene deposition layer in the wellbore will eventually result in an underestimating of the asphaltene layer thickness. For instance, after 60 days of production, there was a 20% difference in asphaltene deposition thickness between the updating and fixed profiles scenarios. Furthermore, closer to the surface, bubble point pressure and lower onset pressure of asphaltene are predicted. In addition, the bubble point pressure and lower onset pressure of asphaltene are predicted closer to the surface. The use of various flow models revealed that the deposition behavior is dependent on the model chosen. In another field study that well was producing through casing, asphaltene deposition increased suddenly at the entrance and then gradually declined by changing casing diameter. Despite the greater maximum asphaltene deposit prediction for casing production, the remaining cross-sectional area was higher than that for tubing production
  9. Keywords:
  10. Asphaltene ; Solubility ; Flow Simulation ; Deposition ; Sediments ; Precipitation ; Collective Behavior ; Spectrometry ; Asphaltene Deposition

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