f Inverse Q filtering for improved well ties

Q causes the absorption of high frequency energy as seismic waves propagate through the earth, as well as phase distortions due to dispersion. Efficient methods for performing inverse Q filtering now exist which allow the variation of Q with depth (Hargreaves, 1992), but these methods require the prior determination of a Q model. Methods to determine Q by measuring absorption in seismic data are inevitably inaccurate (White, 1992). A more accurate method for determining Q is based on the positive drift of traveltimes measured at sonic frequencies (20 khz) compared to seismic frequencies (35 hz) (Leaney and Ulrych, 1988). Dispersion is known to be the major cause of this drift of traveltimes (Stewart et al ., 1984), so the mismatch of integrated sonic and seismic traveltimes can be used to determine average, effective values of Q.