Mechanistic investigation of CO₂-Assisted steam “synergistic oil recovery” in heavy oil reservoirs

ABSTRACT

In late-stage steam flooding of heavy oil reservoirs, challenges such as severe steam channeling, low oil-steam ratio, and rising water cut hinder efficient oil recovery. CO₂-assisted steam injection has become a widely adopted solution for addressing these issues. This study explores the mechanistic aspects of CO₂-assisted steam “synergistic oil recovery.” The research reveals that as dissolved CO₂ content increases, the oil expansion factor reaches a peak of 1.18, leading to significant viscosity reduction and reduced oil density. CO₂ markedly expands the oil-water two-phase flow region, shifting the iso-saturation point rightward and decreasing residual oil saturation from 0.293 to 0.226. Key “synergistic oil recovery” mechanisms include preserving steam dryness, collaborative viscosity reduction, expanding the steam sweep range, mobilizing residual oil with CO₂, and leveraging the demulsification effect of CO₂. Notably, NMR experiments demonstrate a remarkable 13.58% improvement in oil displacement efficiency compared to late-stage steam flooding. This study provides valuable insights into the mechanistic aspects of CO₂-assisted steam “synergistic oil recovery” in heavy oil reservoirs. These findings serve as a theoretical foundation for future field trials and the optimization of CO₂-assisted steam flooding techniques.

KEYWORDS:

• Heavy oil reservoirs
• CO₂-assisted steam flooding
• synergistic mechanisms
• nuclear magnetic resonance
• enhanced oil recovery

Acknowledgements

This work is financially supported by the National Natural Science Foundation of China (Grant No. 52174035).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [52174035].

Notes on contributors

Yuhao Lu

Yuhao Lu(1995—), male, Ph.D. candidate, currently involved in research on techniques and applications for improving extraction efficiency. Email: [email protected]

Jian Wang

Jian Wang(1966—), (corresponding author), Ph.D., professor, doctoral supervisor, currently engaged in research on techniques and applications for improving extraction efficiency. Email: [email protected]

Junheng Wang

Junheng Wang(1996—), Master’s graduate, currently involved in research on techniques and applications for improving extraction efficiency. Email: [email protected]