Design method for recycling output gas after carbon dioxide flooding

The invention discloses a design method for cyclic utilization of output gas after carbon dioxide flooding, which takes miscible-phase flooding required to be realized by cyclic utilization of the output gas as a constraint, and utilizes mature phase state simulation software to simulate the output gas according to an oil-gas miscible-phase process and miscible-phase characteristics. Calculating the oil-gas two-phase surface tension, density ratio and viscosity ratio in the multi-stage swelling process of different output gas components-crude oil to predict the minimum miscible phase pressure of the output gas-crude oil so as to determine the carbon dioxide critical content of the output gas for realizing the miscible phase. According to the method, only crude oil components, produced gas components, crude oil basic physical properties and reservoir temperature are needed, rapid and accurate prediction of produced gas-crude oil minimum miscible pressure is achieved, and produced gas circulation design is comp