Numerical Study of Oil Displacements by Three Hydrocarbon Phases

• Author / Creator

  Xu, Zhongguo

• Solvent injection is a widely used method to enhance oil recovery (EOR). Mixtures of reservoir oil and solvents can exhibit complex multiphase behavior at temperatures typically below 120°F, in which a third solvent-rich liquid (L2) can coexist with the oleic (L1) and gaseous (V) phases. Reliable design of such gas injection requires a detailed understanding of oil recovery mechanisms in three-hydrocarbon-phase flow. In prior research, three-hydrocarbon-phase displacement exhibited a higher level of miscibility with leaner gas (i.e. at a higher level of methane dilution), which resulted in a nonmonotonic trend of oil recovery with respect to gas enrichment. However, no theoretical explanation was given as to why oil displacement was more efficient at a lower level of gas enrichment. Details of oil recovery in three-hydrocarbon-phase flow are not fully understood. This research is concerned with details of oil recovery in three-hydrocarbon-phase flow by use of compositional simulation. First, the mass transfer on multiphase transitions between two and three phases is studied for oil displacement by three hydrocarbon phases. Simple conditions are derived for the multiphase transitions that yield high local displacement efficiency by three hydrocarbon phases. A nonmonotonic trend of oil recovery can occur when local oil displacement by three hydrocarbon phases becomes more efficient, but slower, with decreasing pressure or decreasing gas enrichment. Secondly, an improved method for robust phase identification is developed and implemented in a 1D convective flow simulator with no volume change on mixing. This part of research is important for further confirmation of the oil-displacement mechanisms identified for three-hydrocarbon-phase flow at different flow conditions (e.g., different relative permeabilities). The new method uses tie triangles and their normal unit vectors tabulated as part of the simulation input information. The method can properly recognize five different two-phase regions surrounding the three-phase region; the two two-phase regions that are super-CEP, and the three different two-phase regions that originate with the corresponding edges of the three-phase region in the sub-CEP region. Finally, the displacement mechanisms of three-hydrocarbon-phase flow derived in a preceding part are confirmed by use of different relative permeability models for various oil displacements. Simulation results confirm that the effect of relative permeability on displacement efficiency diminishes as the miscibility level increases. The distance parameters derived before can properly represent the interaction of phase behavior and mobilities since they are derived from mass conservation, not only from thermodynamic conditions.

• Subjects / Keywords

  • EOR
  • Three Hydrocarbon Phases
  • Gas Injection

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3GQ6RC8M

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.