Abstract: Near miscible flooding may make the same displacement effects of low interfacial tension as that of miscible displacement besides reduces injection pressure.Based on the PVT experimental data of multi-contact process and miscibility expansion test by injecting gas from Wei Southwest oilfield group into formation oil in Weizhou 12-1 oilfield,combining the analog computation of PVT properties and phase behavior,the displacement characteristics of muti-contact immiscible and near miscible analyzes and expansion characteristic of accompanying gas injection in Weizhou12-1 oilfield are analyzed.It shows that under present formation pressure(20.47~20.77 MPa),the theoretical miscible pressure of formation oil in Weizhou12-1 oilfield corresponding to is above 39.45 MPa when mole proportion of injecting gas reaches about 0.68 and system reaches a theoretical contacting mixed phase status.Displacement mechanism formed by injecting external transmitting gas into Weizhou12-1 oilfield is multi-contact dynamic non-miscible flooding and weak near miscible flooding.If achieving obvious near miscible flooding and miscible flooding,the injecting pressure should be increased to 40 MPa above.