f Well logs interpolation using zero offset VSP inversion

Zero offset VSP inversion including total wavefield is widely used since several years at Elf Aquitaine, in all cases in which the 1-D propagation hypotheses is sufficiently approched. A new interestmg application of this inversion process concerns its ability to interpolate well logs in zones perturbed by borehole problems, particularly fluid invasions. A sensitivity study shows that zero offset VSP data contain information not only inside the seismic frequency band but also related to the very low frequencies of the impedance log. This property allows interpolation over wide zones. In a case study we compare the impedance log recovered by inversion with a sonic log and an array sonic log. The good agreement of the inversion result with the array sonic log confrms theoretical predictions.