<![CDATA[Extended wellbore storage can be mistakenly interpreted as a reservoir response in gas well testing with surface shut in. This interpretation usually results in false value for permeability, skin and reservoir size and shape. This paper investigates changing wellbore storage in pressure transient testing with surface shut-in in gas well. This study was prompted by the observation, that in gas wells, many of the buildup tests obtained with surface shut-in exhibited complex reservoir model behavior with relatively low skin. The results presented in this paper are based on well test simulation and field data from North Sumatera. This work demonstrates the effect changing wellbore storage on the pressure derivative curve. Knowledge of the expected pressure derivative shape, and duration, will improve the design of buildup tests that will allow enough time for the actual reservoir response to be observed. This will result in a reliable reservoir model and correct estimation of permeability and skin factor.]]>
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