Effect of water saturation on CO₂ minimum miscibility pressure and oil displacement performance

Abstract

The CO₂ miscible flooding is an effective technology for development of low permeability reservoirs due to high oil displacement efficiency. However, CO₂ miscible flooding for tertiary recovery technology typically occur after water flooding. Water hindered the contact and mass transfer of CO₂ and oil, produce water resistance effect. Water can block CO₂ and contact and mass transfer of crude oil (ie water blocking effect). The impact of this effect on the miscibility pressure and oil displacement effect is still unclear. In this study, homogeneous artificial cores with the same permeability as the reservoir were designed according to the miscible mechanism. Subsequently, the minimum miscibility pressure(MMP) between CO₂ and crude oil at different water saturation was measured by the coreflood test. Based on the MMP, CO₂ miscible flooding experiments were conducted by natural cores at different water saturation. The results showed that when the water saturation was 30%, 45%, and 60%, respectively, the corresponding MMP between CO₂ and crude oil was 18.56, 19.48, and 21.76 MPa. The higher the water saturation, the longer the gas breakthrough time. But the oil recovery factor did not rise with the increase of water saturation. When the water saturation was 45%, the oil recovery factor in the miscible flooding experiment was the highest. In addition, the higher the water saturation, the weaker the CO₂ extraction of various components in the crude oil. And the light components below C₅ were most affected by water saturation. The mechanisms underlying these results are discussed. This study contributes to the development of CO₂ miscible flooding reservoir plan.

Graphical abstract

Keywords:

• Water saturation
• barrier effect of water shield
• CO₂ miscible flooding
• minimum miscibility pressure
• components of crude oil

Disclosure statement

The authors declare that they have no competing interest.

Data availability statement

The data used to support the findings of this study are included within the article.

Additional information

Funding

This work was supported by the Natural Foundation of China—Influence mechanism and law of water shield in low permeability sandstone reservoir on CO2-crude oil MMP. (Project No. 52174023), and the Natural Science Foundation of Heilongjiang Province of China—Influence mechanism of water shield barrier effect on CO2-crude oil MMP in low permeability sandstone reservoir (Project No LH2021E015).