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Abstract

It has been observed that wellbore storage changes either increasingly or decreasingly when a well test is run in a producing hydrocarbon well. It causes alterations of the time at which radial flow initiates which normally takes longer time than in wells with constant wellbore storage. This also leads to difficulties in establishing the actual radial flow regime and therefore the interpretation may not be accurate. So far, only for cases of constant wellbore storage the starting time of the radial flow regime can be predicted. In this work, the available mathematical modeling was used to simulate pressure tests with variable wellbore storage to study their behavior so empirical expressions were developed to estimate the starting time of the radial flow regime when wellbore storage is no longer constant. The expressions were validated using synthetic examples.