Experimental research of the effect of CO₂ injection on porous media and fluid property in reservoir

The base of analyzing CO₂ flooding mechanism and potential to improve oil recovery is clearing the effect on porous media and fluid property under the reservoir condition during CO₂ injection.Therefore, static contact experiment and displacement experiment between CO₂ and core is carried out under different pressure. At the meantime, characteristic parameters such as core physical property, microcosmic pore structure, main ion concentration of formation fluid, composition content of produced oil, viscosity and asphaltene content are tested before and after CO₂ injection. The experimental results show that the average porosity of the porous medium increases by 19.16% and the average permeability decreases by 11.23% in the process of CO₂ injection pressure rising from 5 MPa to 20 MPa. Besides, pore space with the diameter of 100-150 μm increases by 9.73% and throat space with the diameter less than 1.5 μm increases by 15.83%, and the hydrophilicity of core significantly enhanced. Meanwhile, the concentration of Ca²⁺ and HCO₃^- in formation water increase with the injection pressure rising. The component content of C₅-C₃₃ in produced crude oil increases first and then remains stable, while its viscosity and asphaltene content decrease rapidly first and then remain unchanged.