In the process of CO

2

injection and storage of a single well in depleted gas reservoirs

the injected CO

2

causes the rebalance among gas

water and solid

and the accompanying CO

2

dissolution

water evaporation and salting out affect the physical properties of the formation near this well. Therefore

taking depleted gas reservoir

in western Sichuan as an example

the SRK-HV equation and salting out model are used to analyze the three-phase change rule during the CO

2

injection process of the depleted gas reservoir. The researches show that during the CO

2

injection process in the constant volume system

with the increase of the number of mole of CO

2

the gas phase pressure increases

the CO

2

solubility gradually increases

and the mole fraction of H

2

O in the gas phase gradually decreases

but the total number of mole of H

2

O in the gas phase continuously increases

indicating that the total evaporation of water increases. In addition

the water phase volume reduction caused by water evaporation is smaller than the initial water phase volume

so the increase of formation water salinity is small. The dissolution of CO

2

accelerates the precipitation of CaCO

3

while inhibiting the precipitation of CaSO

4

and CaSO

4

·2H

2

O. In calcium chloride type formation water

CaCO

3

and CaSO

4

will be separated with the increase of salinity. The research results has certain reference significance for the study of water evaporation and salting out during CO

2

injection in depleted gas reservoirs.