Analysis of Phase Behavior for Steam-Solvent Coinjection for Bitumen Recovery

• Author / Creator

  Sheng, Kai

• Steam-solvent coinjection, if properly implemented, can improve the bitumen recovery efficiency of steam-only injection methods, such as steam-assisted gravity drainage (SAGD). Previous studies have shown that steam-solvent coinjection can reduce residual oil saturation lower than that of SAGD. However, the phase behavior of reservoir fluids during steam-solvent coinjection has not been studied systematically to understand the enhanced displacement efficiency in steam-solvent coinjection. The main objective of this research is to develop a thermodynamics tool to explain the enhanced displacement efficiency obtained by steam-solvent coinjection compared to SAGD. Isobaric ternary phase behavior of water/bitumen/solvent is analyzed to give a general classification method for solvent-containing reservoir fluids. Then, the mechanism of enhanced displacement efficiency by steam-solvent coinjection is explained in a unified way based on the systematic phase behavior study of reservoir fluids. The unified explanation incorporates the phase behavior study of reservoir fluids, mass transfer of the volatile components in reservoir fluids from liquids to vapor, and phase transitions. Finally, the unified explanation of distillation is applied to dimethyl ether (DME), a solvent that has not been studied for steam-solvent coinjection. Two types of phase behavior can be defined for water/bitumen/n-alkane systems for steam-solvent coinjection. For Ternary Type 1, a solvent-rich oleic phase may separate from a bitumen-rich oleic phase in the vicinity of chamber edge, resulting in inefficient dilution of bitumen with the solvent. In contrast, Ternary Type 2 does not show the oleic phase separation, which indicates more effective dissolution of the solvent in bitumen. At 35 bars with the specific bitumen studied, n-C4 and lighter alkanes are classified as Ternary Type 1, and those heavier than n-C4 are classified as Ternary Type 2. Dimethyl ether is classified as a Ternary Type 1 solvent using the same classification scheme. It is found that Ternary Type 1 n-alkanes can yield lower residual oil saturations than Ternary Type 2 n-alkanes under the same operation conditions. Analysis on distillation based on the thermodynamic tool indicates that the enhanced displacement efficiency because of distillation is a result of temperature increase and competition between water and solvent to evaporate. Coinjection of steam with a solvent that has a larger temperature increase during the distillation and is more volatile relative to water can achieve a lower residual oil saturation. Coinjection of steam and DME through the analytical study shows its possible advantage over C3, which is an alkane similar to dimethyl ether in terms of vapor pressure. Compared to C3, DME has a smaller temperature increase for distillation, higher chamber edge temperature, higher displacement efficiency, and lower solvent retention. However, more research is required for more experimental data and modeling to investigate the applicability of DME. The novelties of this research reside in the following items. The phase behavior classification and visualization of water/oil/solvent phase behavior is effectively used to explain the distillation mechanism and solvent dilution in steam-solvent coinjection. The analytical solution developed in this research is a first thermodynamics tool to estimate the displacement efficiency in steam-solvent coinjection, without performing numerical simulation. This research also gives a preliminary study of steam-DME coinjection.

• Subjects / Keywords

  • Steam-solvent coinjection
  • Bitumen recovery
  • Dimethyl ether (DME)
  • Phase behavior
  • Distillation

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3J960M5P

• 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.