Identification of formation interfaces by using wavelet and Fourier transforms

• A non-conventional technique to differentiate the lithological interfaces of the formation.
• Wire-line log data are de-noised by using Wavelet transform.
• Discrete Wavelet Transform (DWT) analysis was applied to remove optimum quantity of noise from very noisy log data (GR log).
• The analysis of selected logs was done by using combination of DWT and FT for the identification of bed boundaries.

The identification of formation interfaces is of prime importance from well log data. The interfaces are not clearly discernible due to the presence of high and low frequency noise in the log response. Accurate bed boundary information is very crucial in hydrocarbon exploration and the problem has received considerable attention and many techniques have been proposed. Frequency spectrum based filtering techniques aids us in interpretation, but usually leads to inaccurate amplification of unwanted components of the log response. Wavelet transform is very effective in denoising the log response and can be carried out to filter low and high frequency components of signal. The use of Fourier and Wavelet transform in denoising the log data for obtaining formation interfaces is demonstrated in this work. The feasibility of the proposed technique is tested so that it can be used in the industry to decipher formation interfaces. The work flow is demonstrated by testing on wells belonging to the Upper Assam Basin, which are self-potential, gamma ray, and resistivity log responses.