Abstract: The wellbore storage coefficient C is always regarded as a constant in conventional well test analysis.It simplified the model, but made it difficult to undertake data analysis in early period of well test.This paper discussed and summarized the variable wellbore storage in well test analysis in detail, and studied the application of Fiar model and error function variable wellbore storage model.These models enabled i t easier to calculate the divergence in true wellbore di-ameter model when skin factor is negative.Also, i t discussed the effect on formation pressure calculation when taking the variable wellbore storage into account.

Key words: Well test interpretation, Wellbore storage, Skin factor, Hole diameter, Formation pressure, Mathmatics model