Combining borehole and surface seismic data for velocity field estimation through slope tomography

Abstract

A joint traveltime and slope (or slowness) tomography method of marine surface reflections and walk-away transmitted arrivals is investigated. Based on our previous developments of 2-D isotropic slope tomography dedicated to reflection data, the transmitted arrivals are added into the inversion scheme. The results of the transmitted arrival tomography are compared to those of the joint (transmitted and reflected arrivals) tomography on synthetic data. Moreover, a quality control (QC) procedure is proposed. Finally, walk-away transmitted arrivals, surface reflected arrivals and joint tomography of both arrivals are applied on real data sets from Oseberg, North Sea. These data include 2-D surface and walk-away lines along the same direction. The resulting velocity fields are used for pre-stack depth migration, allowing us to conclude that joint inversion leads to significantly improved images both in terms of focusing and event location. A key point is that improvements are not restricted in the area covered by transmitted arrivals. As the number of available borehole receivers is small, this case study demonstrates the strong impact direct arrivals that may have on depth imaging.