Vp/Vs ratio estimation from joint PP-PS inversion of 3D VSP seismic data

A workflow to derive Vp/Vs and acoustic impedance volumes from joint PP-PS inversion of seismic data is applied to 3D VSP data. PP and PS depth migrated VSP volumes, converted to PP time, are first sequentially inverted for acoustic and PS elastic impedance respectively. In a second step the main reservoir horizons are interpreted for each volume. The PS volume is then transformed in time so that the picked horizons coincide in the PP and PS datasets. The resulting data are jointly inverted for acoustic impedance and Vp/Vs. This workflow was applied to two 3D VSP datasets, recently acquired in the Arabian Gulf, to improve the delineation of thin sand stringers for optimized horizontal well placement. The 3D VSP inversion results were compared to the conventional elastic inversion of PP OBC data. When OBC data are good, no significant resolution improvement was observed on the 3D VSP results. In an area where the OBC data quality was low, the 3D VSP provided a superior image in the proximity of the well.