Dissolution characteristics and mechanisms of CH

4

CO

2

and N

2

in crude oil are studied through solubility experiments

resulting in the following understandings: ① hydrocarbons play a key role in the process of gas dissolution in crude oil

while macromolecular substances

such as colloid and asphaltene

have a little influences on the gas solubility.② Gas molecules and macromolecular substances in crude oil can form adduct molecules;this process can be treated as an apparent chemical reaction and its reaction degree can be described by an equilibrium constant K.③ Early formed gas-hydrocarbon adduct molecules have certain solvency to subsequently formed gas molecules

which can be described by a secondary dissolving coefficient α.④ Physical properties of crude oil can be characterized by the density(ρ

o

) of surface crude oil and the mass fraction(x

T

) and average molecular weight(M

T

) of hydrocarbons in crude oil.Combined with other factors that have influences on gas dissolution

the theoretical equation of gas'mole solubility in crude oil and that of gas-oil ratio in crude oil are derived.Comparison with experimental data shows that calculated and measured values have a good consistency.