Use of Wavelet Transformation for Geophysical Well-Log Data Analysis

Geophysical well-log (bore-hole) data represent the rock physical properties as a function of depth measured in a well. They aid in demarcating the subsurface horizons, identifying abrupt changes in physical properties of rocks and locating cyclicity (if any) in stratal succession. Rocks document their depositional history, which geoscientists unfold by analyzing different geophysical data, such as well-log data, seismic data, etc. We have applied continuous wavelet transformation technique on one type of well-log data (gamma ray log) from three wells located in Bombay High oil field, India. Our analyses have helped to identify the discontinuities, detect the horizons and check the presence of cyclic pattern (if any) in deposition. Among various wavelets that we have used, the Morlet wavelet has proved to be most appropriate to resolve the marker horizons in gamma ray log data. We also conclude that the choice of wavelet is dependent upon the rock intrinsic properties that vary greatly in the space domain (with varying depth).