Reaction Experiments of CO2-Rock-Water-Crude Oil and Its Effect on CO2 EOR

During CO2 flooding in reservoir, CO2 dissolves in water and forms to carbonic acid, which will react with formation water, rock and crude oil as follows: carbonic acid reacts with calcium and magnesium ions in formation water to produce inorganic salt precipitation, reacts with colloid and asphaltene to produce asphaltene precipitation, and reacts with rock to produce dissolution. The above reaction will affect the development effect of CO2 flooding. Through laboratory experiments, the mechanism and main controlling factors of inorganic salt precipitation formed by CO2 and formation water are analyzed, and the quantitative characterization model of inorganic salt precipitation is established considering temperature, pressure and ion content of formation water; the interaction mechanism between CO2 and crude oil is clarified, and the mathematical characterization model of asphaltene precipitation is established considering temperature, pressure and asphaltene content. Based on the mechanism of rock action, a mathematical model for quantitatively describing the amount of dissolution is established. Finally, the influence of inorganic salt precipitation, asphaltene precipitation and dissolution on enhanced recovery of CO2 flooding is analyzed by using reservoir numerical simulation method and taking typical reservoirs as an example. The results show that the distribution of asphaltene mainly concentrates near gas injection wells, but the total asphaltene has little effect on oil recovery; the precipitation of inorganic salt gradually increases from gas injection wells to oil production wells, and the precipitation of inorganic salt near gas injection wells is smaller, the dissolution effect near gas injection wells is stronger, and the effect of dissolution on oil recovery is greater.