VSP-Derived Vp/Vs Ratios for Pressure Prediction ahead of the Bit

F-21 VSP-DERIVED VP/VS RATIOS FOR PRESSURE PREDICTION AHEAD OF THE BIT Summary 1 VSP techniques have long held out the promise of ahead-of-the-bit pressure predictions but a variety of data acquisition and interpretation issues have limited this potentially important application. In particular P-wave velocities ahead of the bit if determined from inversion of upcoming reflected amplitudes contain the assumption that the up-hole velocity trend can be simply extrapolated downward. This assumption is inappropriate in a case where a deeper pressure seal causes a reversal of the trend. However a simple interpretation technique (Thomsen 1992) requiring only the picking and registration