Abstract: Some pressure buildup test curves in Karamay oilfield exhibit phase segragation phenomenon to various extent, which therefore distorted the shape of well test curves, and also covered the true properties of formation.If treated improperly, the erroneous conclusion is likely to occur.In order to enable pressure buildup data to correctly evaluate the reservoir, the phase segragation effect was analysed in details.Its forming mechanism was analysed by using actual data, and the corresponding solution obtained.

Key words: Karamay oilfield, Pressure buildup analysis, Well testing, Curve, Phase state study