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Investigating the Role of Molecular Diffusion on Oil Recovery by Gas Injection Into Fractured Reservoirs and Scaling Up the Experimental Data

Sistan, Morteza | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55723 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ghazanfari, Mohammad Hossein; Jamshidi, Saeed
  7. Abstract:
  8. Fracture reservoir modeling is an important subject since a lot of oil and gas resources around the world are preserved in them. One of the enhanced oil recovery methods in these reservoirs is gas injection and especially CO2 injection because of environmental issues. In one part of this research, a new diffusion mechanism called “double cross-phase diffusion” is introduced and applied to simulate the non-equilibrium gas injection process into fractured rocks. This new mechanism represents additional multicomponent gas diffusion into the crude oil through the water phase, existing in porous media as initial water saturation. Therefore, a lab-scale simulator, by implementing the generalized Fick’s law of multicomponent diffusion, is developed and used for predicting the experimental data of oil recovery during CO2 injection in chalk fractured rocks in the presence of initial water saturation. The results revealed a significant difference in the oil recovery predicted by the model when the double cross-phase diffusion mechanism is considered. The transient behavior of produced oil composition, predicted by the simulation model, is matched well with the experimental data. The portion of active oil recovery mechanisms in the system has been evaluated and observed that the molecular diffusion mechanism induced 75.4% of the total oil transfer rate in the initial time oil recovery, in which 23.1% of this value was supplied by the double cross-phase diffusion mechanism, that is an interesting founding. Results of sensitivity analysis showed that by increasing the initial water saturation, the impact of the double cross-phase diffusion mechanism on oil recovery increases. Using pressure decay tests for the calculation of molecular diffusion coefficients for each component in oil and gas phases is another subject presented in this research. The studied systems are 1) Methane-Nitrogen-Hexane 2) Methane-Nitrogen-crude oil 3) Methane-crude oil in the reservoir condition. The formulation which is applied for pressure decay test modeling is different from other studies that used effective diffusion coefficient. In this modeling, the continuity equation and Stefan-Maxwell model were applied for gas and oil phases separately and were solved with chemical potential equilibrium for all the components in the interface. The simulation results are molecular diffusion coefficients for each component in oil and gas phases and also prediction of components concentration in the height of PVT cell. In the upscaling part, IA was used to introduce 8 dimensionless groups for immiscible gas injection when gravity drainage mechanism was present. When IA for non-equilibrium gas injection was applied, dimensionless groups increased to 10. If the molecular diffusion transfer function was included, the dimensionless groups became 11. Therefore, 4 new dimensionless groups were introduced which was an interesting finding. For a 2-block system simulation, a 1-block model was extended to a 2-block and oil reinfiltration was considered. Also, sensitivity analysis was done to investigate the effect of permeability, gas injection rate, and initial water saturation on oil recovery from the 2-block system. The results of this work illustrate that the double cross-phase diffusion mechanism introduced in this study plays a significant role in the simulation. Therefore, it is suggested to apply this mechanism in professional reservoir simulators, especially in the CO2 injection process. The results of pressure decay modeling indicate that diffusion coefficients reported as vector form are compatible with the commercial simulator input keyword which is a valuable outcome.
  9. Keywords:
  10. Fractured Reservoirs ; Molecular Diffusion ; Scaling Up ; Fick's Law ; Generalized Fick’s Law ; Stefan-Maxwell Model ; Pressure Decay Method ; Irreversible Thermodynamic

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