Method for determining reasonable gas injection pressure of liquid carbon dioxide phase change displacement coal seam

The invention discloses a method for determining reasonable pressure injection pressure of liquid carbon dioxide phase change displacement coal seam gas. The method specifically comprises the following steps: S1, carrying out an isothermal adsorption experiment on a target coal seam coal sample; s2, respectively calculating virtual saturated vapor pressure of CO2 and CH4 gas; s3, establishing a relationship between gas adsorption potential and gas adsorption equilibrium pressure; s4, the density of CO2 and the density of CH4 are calculated respectively; s5, respectively calculating adsorption spaces of CO2 and CH4 in the coal body; s6, establishing a relational expression between the adsorption potential and the adsorption space of the two gases; s7, reasonable replacement pressure is determined; s8, reasonable displacement pressure is determined; s9, calculating a CO2 seepage coefficient; s10, determining a reasonable seepage pressure; and S11, reasonable injection pressure is determined. The method provides