A comprehensive research on the effect of heavy oil properties by carbon dioxide and the evolution of enhanced efficiency in assisted steam flooding

Abstract

Under the framework of carbon capture, utilization, and storage-enhanced oil recovery (CCUS-EOR) technology, a strategy is proposed to enhance the heavy oil recovery during the late stage of steam flooding by utilizing carbon dioxide (CO₂) to regulate the physical properties of heavy oil and strengthen assisted steam flooding. Taking the F Block in Xinjiang Oilfield, China as example, this study systematically examined the regulatory effect of CO₂ on the high-pressure properties of heavy oil. Additionally, two-dimensional visual physical models and sand-packed physical models were utilized to conduct an in-depth analysis of the sweep characteristics, microscopic displacement mechanisms, and oil recovery of CO₂-assisted steam flooding. The results indicate that CO₂ significantly improves the physical properties of heavy oil. The bubble point pressure increases with the amount of dissolved CO₂, while the expansion coefficient initially increases and then decreases with rising CO₂ injection pressure. Under the influence of CO₂, the viscosity reduction of heavy oil reached 27.16 %, and the relative density decreased to as low as 0.907. Injecting CO₂ during the late stage of steam flooding mitigates steam channeling issues. CO₂ dissolves and diffuses into the heavy oil, altering the interfacial film properties of emulsions and facilitating emulsion breakdown. These combined effects alleviate the oil trapping effect within the pores of low-permeability regions, significantly increasing the swept area. As a result, the areal sweep efficiency improves by 7.47 %, while the residual oil saturation is minimized to the greatest possible extent. The oil recovery improved from 39.13 % to 50.76 %, representing an 11.63 % enhancement compared to steam flooding alone. This study highlights the potential of CO₂ injection to enhance oil recovery during the late stage of steam flooding in heavy oil reservoirs. It also provides valuable insights into the regulatory effects of CO₂ on the physical properties of heavy oil and the underlying microscopic mechanisms.