In the equation for skin factor during the pressure buildup, P, is measured just before shutting in the well, and plhr is obtained from the straight-line portion (extrapolated if necessary) of the buildup curve one hour after shut-in (see Figure 5-138a). Similarly, the straight-line portion of the drawdown data must be extrapolated to one hour if the data do not fall on the semilog straight-line (see Figure 5-138b).
