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Core Scale Mechanistic Investigation of the Effect of Gas Composition on Enhanced Oil Recovery Mechanisms during Injection at Different Miscibility Conditions

Shokri Nazarabad, Farshad | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55150 (06)
  4. University: Sharif University of Technolog
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Fatemi, Mobeen
  7. Abstract:
  8. The gas injection is one of the most common methods of increasing recovery from oil reservoirs, especially when a suitable source for gas is available. For example, available sources of carbon dioxide or associated gas produced from the reservoir or adjacent reservoirs. In general, the gas injection may be miscible or immiscible, which is a function of the type and composition of the gas-oil and the reservoir conditions in terms of temperature and pressure. In miscible gas injection, different mechanisms such as molecular diffusion of gas in oil or evaporation of lighter components of oil in gas and condensation of heavier components of gas in the oil phase can be shown. To occur of such mechanisms has created a new phase in the oil-gas surface, which can improve the process of oil displacement at the macro and micro scales. Also, in the long term, the miscible injection can improve the oil recovery by changing the properties of oil, such as viscosity, density, etc.The main purpose of this study, is to calculate the minimum miscible pressure and investigate the mechanisms affecting oil recovery for various injection gases at the core and matrix-fracture system.An oil sample from one of the reservoirs in southwestern of Iran was considered as the reservoir fluid. Regression of the Peng-Robinson equation of state was performed for available laboratory data to increase the accuracy of the equation in predicting the physical properties of oil and gas. The composition of the current injected gas into the reservoir was considered, then to investigate the effect of the injection fluid composition on the oil recovery mechanisms, this gas was combined with carbon dioxide in different ratios.Then, the minimum miscible pressure of the oil and different gases was calculated using the PVTsim software and Eclipse compositional simulation. With increasing mole percentage of carbon dioxide in the injected gas, the minimum miscible pressure of oil and gas decreased. The results of the Eclipse compositional simulator were considered as gas injection pressures. Oil recovery mechanisms, for different gases at the core scale were investigated.In methane injection, evaporation of light components of oil into the gas and for other gases, the combination of condensation heavy components of gas into the oil and evaporation of oil components into the gas was identified as the dominant mechanisms. With increasing mole percentage of carbon dioxide in the injected gas, the gas front approached the complete miscible of the two phases and the intensity of the mentioned mechanisms also increased.Also, for the matrix-fracture system, the mechanisms of oil recovery in the injection of different gases were investigated. Similar results were obtained with the core model. Due to the high permeability of the fracture, to produce oil from the matrix blocks required more time and volume of injected gas than the core model. In general, it can be said that the dominant mechanism of oil recovery in this study is a combination of condensation the gas phase components into oil and evaporation of oil components into gas, which changes its intensity and weakness based on the mole percentage of carbon dioxide in the injected gas.
  9. Keywords:
  10. Gas Injection ; Compositional Simulation ; Immiscible Injection ; Miscible Injection ; Enhanced Oil Recovery ; Minimum Oil and Gas Miscible Pressure ; Gas Injection Simulation

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