During the afterflow of a pressure build up in a gas well test a unique pressure response is created by the declining rate dependent skin. This paper describes a method to include the effect of the declining rate dependent skin in the response of analytical well models. This results not only in an improved analysis by regression, but also in the possibility to obtain the rate dependent skin from the afterflow response of a single rate gas well test with build up. The accuracy of the resulting rate dependent ~kin values has been validated in some ten multi-rate test analyses.

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