Study of the oil recovery trends by imbibition in low-permeability cores under high-pressure CO₂

During the development of CO₂ injection in low-permeability reservoirs, carbonated water formed after CO₂ dissolves in water can effectively improve the imbibition effect, and thus improve the reservoir development benefit. By measuring the oil-water interfacial tension, contact angle and imbibition recovery factor, the effect of temperature and pressure on imbibition recovery in low-permeability cores under high-pressure CO₂ was investigated. The results show that increasing temperature and CO₂ pressure can improve oil-water interface characteristics and enhance imbibition recovery. At 8 MPa, the temperature increases from 20 ℃ to 80 ℃, the interfacial tension increases by 2.25 mN·m^-1, and the contact angle decreases by 15.2°. The influence of temperature on oil-water interface characteristics is stronger than that of CO₂ solubility. With the increase of temperature, CO₂ solubility decreases, but the interfacial tension increases, the hydrophilicity of rock enhances, and the fluidity of crude oil increases, so the imbibition efficiency increases. At 80 ℃, the pressure increases from 4 MPa to 10 MPa, the interfacial tension decreases by 3 mN·m^-1, and the contact angle decreases by 18.4°. Pressure mainly affects the oil-water interface characteristics by changing the CO₂ solubility in the liquid phase. With the increase of pressure, the CO₂ solubility increases, the interfacial tension decreases, the hydrophilicity of rock enhances, the fluidity of crude oil also increases, so the imbibition efficiency increases effectively. Heating and pressurization have a certain synergistic effect on improving imbibition efficiency. Under the combined action of the two, although the interfacial tension only slightly decreases, the hydrophilicity of the rock enhances significantly, which accelerates the escape of crude oil in the matrix pore throat and effectively improves the imbibition recovery in low-permeability cores. The research results enrich the imbibition production mechanism, and can provide theoretical reference for CO₂ injection development in low-permeability reservoirs.