Research On The Mechanism CO₂ Flooding On F Reservoir With Ultra-low Permeability In Daqing

F reservoir in Daqing belongs to the kind of reservoir with ultra-low permeability. Such reservoir has the features of small pore throat size, big specific surface, the existence of quasi-threshold pressure gradient, high water injection pressure and weak water absorbing capacity. When water reaches injection wells, oil production index and fluid production index decrease quickly. Production rate and oil recovery efficiency get lower. On the condition of existing development, it is hard to get considerable economic benefits. It is urgent to explore the flexibility of injecting gas. As a significant measure of gas flooding, CO₂ flooding can enhance oil displacement efficiency. However, the development regulation and technological limit of CO₂ flooding on F reservoir are not clear yet. Aiming at the reservoir of ultra-low permeability, the thesis carries out amounts of physical simulation experiments, which are conducted under formation condition, to analyze the mechanism of CO₂ flooding.The results show that after injecting CO₂, saturation pressure of formation oil in F reservoir gets enhanced, viscosity of formation oil is reduced, and irreducible water saturation gets increased. So the physical property of crude oil gets better, which makes it easier to be displaced. When the production pressure reaches 26.88 MPa, CO₂ can adequately mix with crude oil to obtain better oil recovery efficiency. Compared with water flooding, the start-up pressure of CO₂ flooding is smaller, and the injectability is stronger. The lower the formation permeability is, the better the effect of CO₂ flooding has. In the meantime, the injection of CO₂ can alter the PH value inner rocks. Thus a series of chemical reactions happen to make the rocks’ permeability and porosity larger and the its wettability stronger. In the process of CO₂ flooding, light components of crude oil are apt to be extracted, which decreases the interfacial tension between oil and gas and increases the mobility of crude oil. Therefore, the oil displacement efficiency gets enhanced.By means of the physical simulation experiment and the analysis of the mechanism of CO₂ flooding, we prove the feasibility of CO₂ flooding on the reservoirs of ultra-low permeability.Finally CO₂ flooding is fit for the development of F reservoir.