Study of Near-Borehole Structure from Subtractive and Differential Vertical Time-Depth Curves

Adding static shifts to the number of unknowns in travel times inversion would not lead to the success, especially in processing of zero-offset vertical time-depth curves and also in the case of variation of the static shifts during the borehole measurements. Suggested alternative approach consists in using the subtractive vertical time-depth curves, obtained by calculating of time arrival differences for different waves recorded in the same receiver points. Reduced subtractive time-depth curves allow determining the layer model with higher assurance comparably with the one obtained for single time-depth curves. In addition, using the differences between time arrivals of the same wave from the same source to different receiver points is suggested. There through, influence<br>of static shifts on the determined seismic parameters in the limits of the accepted model is eliminated. Algorithms and computer programs developed by the authors are based on applying of optimization methods to the differential timedepth curves for waves of different types and classes. Efficiency of the programs was confirmed by the results of model and experimental studies.