Identification of stratigraphic formation interfaces using wavelet and Fourier transforms

The purpose of this study was to identify the formation interfaces from geophysical well log data using the wavelet transform, and a combination of the wavelet transform and the Fourier transform methods. In the wavelet transform method, the identification of formation interfaces is based on the wavelet coefficients from the wavelet transform of spontaneous potential (SP) log and gamma ray (GR) log data. In the combination of the wavelet transform and the Fourier transform methods, the wavelet transform, spectrum analysis, and logarithmic transform of well logs were applied to the SP and GR log data successively to obtain clear signals for identifying the stratigraphic formation interface. In this study, a set of ideal log data was first created and analyzed to test the validity of the developed procedures. In analyzing the SP and GR logs from a field, both the wavelet transform method and conventional well log analysis showed similar results. The results from a combination of the wavelet transform and the Fourier transform methods, however, were better than those from the wavelet transform method and the conventional well log analysis.