when the injection period is relatively short and only the second stabilization is detectable hydrocarbon virgin area the bi phase skin must be evaluated using a numerical well testing simulator which considers the fluid removal equations and the relative permeability curves it is possible to reproduce the trend of the injection and fall off pressures through the numerical simulator establishing s 0 a conventional interpretation of the data generated by the simulator produces a skin value which proves to be the only bi phase skin s s 0 having been established in the simulator c in the absence of a numerical simulator it is possible to evaluate in a first approximation the bi phase skin with the formula of the skin factor from a radial composite is calculated once the fluid viscosity u03bc inj and u03bc hc and the relative permeabilities end points k r inj max and k r hc max are known the interface radius can be evaluated in relation to the volume injected evaluation of the skin factor s as in conventional well testing with the exception of the previous item a wherein s is obtained directly the skin factor s must be evaluated by subtracting the component s from the total skin according to.