Abstract: Mixing of injected gas and reservoir oil will change the initial saturation pressure, affect the deliverability of the oil. And the change of saturation pressure could affect the performance of volatile oil reservoir. This paper analyzes the effect of injected gas on saturation pressure of volatile crude reservoir under the assumed direct and complete mixing between injected gas and crude in PVT test by using the balance theory of gas-liquid two phases and field data, without consideration of effect of porous media on phase behavior. The results show that when natural gas, methane or nitrogen are injected into volatile oil sample, the oil saturation pressure will increase with incremental injected gas volume, of which the nitrogen injection assures the biggest saturation pressure, adding intermediates injected volume tends to decrease of the saturation pressure, whereas increasing overall injected volume would enable the miscibility pressure of the injected gas and crude oil to increase.

Key words: saturation pressure, gas injection, miscible flooding, volatile oil reservoir