Crosshole elastic WTW inversion of the McElroy data

We apply the elastic wave equation traveltime and waveform inversion (elastic WTW) method to the McElroy crosshole data. These data are characterized by a well offset of 184 ft and a wide-band source wavelet (250-2000 HZ). Numerical tests indicate that the following processing steps are necessary, but not sufficient, for successful waveform inversion: FK filtering of the upgoing and downgoing waves, FK-fan filter extraction of the PP and SS reflections, and balancing the amplitudes of the upgoing and downgoing reflections. TO reduce the complexity of the data we use a divide and conquer strategy, i.e., extract the PP reflections and SS reflections, then invert each wave mode separately. Numerical results show that the vertical spatial resolution of the WTW P-wave and S-wave tomograms are approximately 7-10 feet and 4 feet, respectively. This compares favorably to the 40-50 feet vertical resolution of the P-velocity tomogram obtained from the first arrival traveltime data. There is good to very good agreement between the sonic logs and the velocity from the WTW tomogram. These results demonstrate that high resolution Poisson ratio, S-velocity, and P-velocity tomograms can be extracted from crosshole data, and therefore can be used for lithological interpretation.