Abstract: Type curves and pressure dirivatives are widely used in modern well test analysis,The estimation of low noisy pressure dirivative is however a difficult problem.A“WINDOW"technique is introduced in this paper for estimating pressure dirivatives.An algrithm for variable rate test data is also presented. low noisy dirivatives can be obtained with the techniques.

Key words: well test analysis, Pressure dirlvative, Algarithm