In tertiary-recovery projects, kinds of measure are adopted to enhance oil recovery. One of them is alternate gas and water injection. After this measure, the displacement fluid in the reservoir becomes a gas-liquid mixture. Well test analysis for such multiphase displacement reservoir is still difficult.
In this paper, a mathematical model of the composite reservoir is established. The dimensionless wellbore pressure drop is solved analytically by using the Laplace transformation with numerical inversion. The corresponding type curves for appropriating injection/producing well are given. Moreover, the numerical solution is obtained by numerical simulation that considers effect of saturation distribution. By combining numerical method with analytical method, the inner and outer region mobility, skin factor, wellbore storage constant and front radius can be determined. Together with field examples, the paper analyzes pressure transient data of injection well and producing well.