<![CDATA[Extended wellbore storage can be mistakenly interpreted as a reservoir response in gaswell testing with surface shut in. This interpretation usually results in false value for per-meability, skin and reservoir si:e and shape. This paper investigates changing wellbore storage in pressure transient testing withsurface shut-in in gas well. This study was prompted by the observation, that in gas wells,rnany of the buildup tests obtained with surface shut-in exhibited complex reservoir modelbehavior with relatively low skin. The results presented in this paper are based on well test simulation and field data fromNorth Sumatera. This work demonstrates the effect changing wellbore storage on the pres-sure derivative curve. Knowledge of the expected pressure derivative shape, and duration,will improve the design of buildup tests that will allow enough tirne for the actual reservoirresponse to be observed. This will result in a reliable reservoir model and correct estima-tion of permeability and skin factor.]]>
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