The produced GOR is a key index for the development and design of gas flooding reservoirs. On the basis of confirming that there are five sources of gas production in the whole life cycle of gas flooding

the prediction formula of produced GOR in low permeability reservoirs matching with three development stages is proposed. From gas injection to pre-gas production

the produced GOR is mainly controlled by the initial dissolved GOR of the reservoir fluid

and method of determining the equivalent GOR of water-soluble gas is given. The produced GOR in the stage from pre-gas production to gas channeling is affected by the gas dissolved capacity of ″oil bank″. The method of describing the physical p

roperty of gas flooding″oil bank″ in low permeability reservoirs can be used for reference to determine dissolved GOR of gas flooding″oil bank″. The change of produced GOR after gas channeling is determined by the GOR formed by free gas

and its prediction based on the understanding that the pore space released by the produced liquids would be filled with the injected gas and water. It is calculated by oil and gas fractional flow equation

Corey

'

s model and Stone

'

s equation combined with concepts of gas flooding increasing multiple in low permeability reservoir

and slug size ratio of water-gas during water alternating gas injection. The reservoir engineering method of produced GOR prediction taking the form of ″three-stages″ has been verified by the field test of CO

2

miscible flooding. It can be used in gas injection development planning design

optimization of oil production process or gas injection storage potential evaluation.