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Investigation of the Effect of Asphaltene on Interfacial Tension Behavior of CO2/Oil Systems during CO2 Injection into Asphaltenic Oil Reservoirs

Mahdavi, Ehsan | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46041 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Taghikhani, Vahid; Ayatollahi, Shahabeddin
  7. Abstract:
  8. Interfacial Tension (IFT) behavior of crude oil/CO2 system is recognized as the main factor affecting the efficiency of CO2 flooding during enhanced oil recovery (EOR) process. Adding paraffin group hydrocarbon to asphaltenic crude oils as an asphaltene precipitant component is aimed to mimic asphaltene precipitation process during crude oil production and transportation. Asphaltene precipitation would critically effects the IFT behavior of crude oil/CO2 systems. In the first part of this study, the equilibrium densities of oil samples which contain different heptane ratio were measured at different pressures and the temperature of 323 K. Then, the equilibrium IFT between CO2 and the crude oil samples was measured using the axisymmetric drop shape analysis (ADSA) technique. This investigation was followed by measuring the minimum miscibility pressure (MMP) of the oil/CO2 systems using the vanishing interfacial tension (VIT) technique. The results showed that density increases linearly as pressure increases. Moreover at a constant pressure and temperature, the density was linearly decreased with n-heptane content of the crude oil sample. Linear correlations between density, n-heptane content and pressure at the temperature of 323 K for each oil samples were also noticed. The results of IFT tests indicated that asphaltenic crude oil samples have two slope IFT-pressure behavior. It was found that for oil sample with high asphaltene content (weight %: 9), the higher the n-heptane content of the oil sample is, the lower is the pressure of the IFT’s slope change, while for low asphaltenic oil sample (weight %: 0.56) increasing of n-heptane has little effect on the point of IFT’s slope change. Consequently, it was found that asphaltenes increase the rate and magnitude of the light component extraction in oil/CO2 systems. The experimental results showed that the MMP of the oil samples decreased linearly with the n-heptane content of the oil sample. The linear relation between the MMP and n-heptane content revealed the crucial role of paraffinic group as the controlling miscibility component of the crude oils.
    The main purpose of the second part of this study is to explore the effects of different asphaltene structures on the IFT behavior of CO2/asphaltenic oil system.The results show that the point of IFT’s slope change for oil samples containing different asphaltene types, does not occur at the same pressure.It can be attributed to the different tendency of asphaltenes to aggregate and create larger particle. It can be deduced that the IFT behavior of asphaltenic oil samples depends critically on the tendency of asphaltene molecules to accumulate at the gas−oil interface, the intensity of precipitations, and their structure at the interface. On the other word, the different molecular structure of asphaltenes is the main reasonof the difference in IFT behavior. Also, the experimental results show that the miscibility condition for the oil sample with higherpotential of asphaltene precipitation, is harder to be achieved
  9. Keywords:
  10. Carbon Dioxide Injection ; Interfacial Tension ; Paraffins ; Miscibility ; Interfacial Tension ; Asphaltenic Oil

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