Abstract: The effect of medium injection on PVT properties of crude is studied as one of evaluation means in laboratory for EOR by gas injec-tion process. Injection of rich gas and N2 followed by study of the variations of PVT parameters of crude is the basis of making laboratory evalua-tions for different displacement processes as trailing edge miscible flooding,front miscible flooding and non-miscible flooding. On the basis ofPVT analysis of actual light oil, a rich gas and N2 injection experiment and N2 multi-contact experiment are studied, respectively, including com-parison of variations of oil phase behavior, saturated pressure, viscosity, B,, GOR and p. after injection of these two gases. In addition, the effectof N, extraction on the PVT properties is analyzed. The results show that similar variation of PVT properties for rich gas and N2 injection occurswhen the one- contact miscible flooding, but N, is not so good as rich gas in improvement of crude viscosity, volume factor and density, as a resultof quick increase of oil saturated pressure; also, under N flooding, the trailing edge miscible formation crude will become heavy quickly, result-ing i0peloc 2fletichessbyca dooding lionnacherongt laDEnd ludilig lhingnisoide diplacigheht.reserved.

Key words: gas injection, phase behavior, EOR, nitrogen, displacement