Abstract: The key of sequence stratigraphy analysis lies in recognizing sequence boundaries of different levels. Parasequence is the minimum unit of sequence stratigraphy analysis of well-logging. Logging curves changed abruptly due to obvious variation of physical properties at the interface of parasequence unit. The mutation can be revealed clearly by wavelet transform of logging data. Example was taken from the No.3 sequence in the third middle member of Shahejie Formation in a well of Shengli oilfield，the SP data were processed by two-scale wavelet transform using quadric spline wavelet. With this transformation the logging data were expended from one dimensional depth space into two dimensional depth-scale space and wavelet coefficient curves on different scales were obtained. When the optimum decomposed-scale was determined, the interface of parasequence unit can be recognized correctly according to the position of wavelet modulus and the result was finer than that of manual recognition. The research was of important significance in quantitative sequence demarcation at different levels.

Key words: logging data, wavelet transform, sequence stratigraphy, parasequence, wavelet modulus