In order to study the effect of CO

2

flooding on the physical properties of crude oil

understand the mechanism of CO

2

flooding

and provide theoretical basis for the analysis of field test results of CO

2

flooding

the field test of CO

2

flooding in Huang 3 block of Jiyuan oilfield in Changqing was carried out by column chromatography and gas chromatography-mass spectrometry. The physical properties of crude oil produced before

and after CO

2

flooding in Huang 3 block of Jiyuan oilfield

Changqing

were studied in detail by means of column chromatography

gas chromatography and mass spectrometry method and other methods. The changes of crude oil group content

different carbon chain alkanes content

solidification point and viscosity-temperature curve were mainly investigated. The experimental results show that after CO

2

injection

the alkane fraction of crude oil first decreases and then increases

while the non-hydrocarbon and asphaltene fraction first increases and then decreases; the light alkane（C

8

—C

16

） in the alkane fraction of crude oil first decreases and then increases

the heavy alkane（C

17

—C

40

） content first increases and then decreases; the pour point of crude oil first increases and then decreases

and the viscosity of crude oil at low temperature（35 ℃） increased slightly

but there was no obvious change at high temperature. The above results accord with the mechanism of CO

2

miscible flooding. The change of crude oil physical properties is the result of the interaction of CO

2

extraction mechanism. Through the above research

it provides data support for understanding the mechanism of CO

2

flooding

and provides a certain basis for further formulating plans to improve the efficiency of CO

2

flooding.