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Effect of Nitrogen Injection on Phase Behavior and Asphaltene Instability

Moradi, Siyamak | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 41702 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Rashtchian, Davood; Dabir, Bahram; Emadi, Mohammad Ali
  7. Abstract:
  8. Nitrogen injection is a promising enhanced oil recovery process. Asphaltene precipitation during miscible gas injection is a common problem in oilfields throughout the world. In this work, a comprehensive study is conducted on effect of gas injection on phase behavior and asphaltene instability of live oil samples. Effects of oil API, gas type and concentration, pressure and temperature are studied under natural depletion and nitrogen injection processes by means of high pressure filtration and a photographic procedure coupled with image analysis. Filtration results show that nitrogen destabilizes asphaltenes more compared to methane and the problem is more severe for heavier crude samples. Bimodal histograms of particle size distribution show two agglomeration mechanisms; cluster aggregation dominant around bubble point pressure and diffusion limited far away. Fractal structure of aggregates is also altered by gas injection; it is observed that the flocs grow in size and become more compact and organized when the cluster aggregation overcomes. Numerous models have been developed for prediction of asphaltene precipitation including thermodynamic models, colloidal models, micelle models, and scaling approach. Besides applying common thermodynamic models, a new scaling equation is presented to predict asphaltene precipitation under HPHT gas injection. Extensive published data from literature are also used in model development. The scaling approach is attractive because it is simple and complex asphaltene properties are not involved in the calculations. Moreover, the proposed model provides universal parameters for different fluid samples in a wide range of pressure and temperature that makes it novel for evaluation of future gas injection projects when simple PVT data are available.
  9. Keywords:
  10. Nitrogen Flooding ; Asphaltene Precipitation ; Population Balance ; Screening Analysis ; Aggregate Size Distribution ; Fractal Structure

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