SAND SHALE DIFFERENTIATION USING SHEAR-WAVE VELOCITY FROM P-S SEISMICDATA/

Linear equations relate small changes in rock properties across an int erface to seismic reflectivity (Aki and Richards, 1980). These equatio ns for P-P and P-S wave reflectivity can be inverted to provide estima tes of density, P-wave and S-wave velocity. We use a least-squares app roach, similar to the Smith and Gidlow (1987) weighted stack, with P-S reflectivity to find the S-wave velocity. The algorithm has been test ed on field data from the Blackfoot field in southern Alberta. In this case, estimated S-wave velocities rise from about 2200 m/s to 2400 m/ s with a shale to sand transition. The P-wave to S-wave velocity ratio also decreases from about 1.9 to about 1.5.