Advanced Borehole Seismic Imaging of Transition-Zone Subsurface Structures

Transition zone seismic surveys collected over a subsurface reef structure present significant subsurface imaging challenges in producing reliable interpretations for reservoir assessment. In order to aid the reservoir description, the complete vertical and horizontal borehole trajectory was instrumented with 3C receivers, while simultaneously recording 3C receivers in shallow vertical wells. Even with a limited source layout, such a source and receiver geometry allows us to extract a multitude of information about the near surface and deeper subsurface. While traditional standard imaging is challenging with this geometry, interferometric processing, imaging and analysis allows us to obtain valuable reservoir information. In the following we briefly introduce the geologic setting and data acquisition aspects, and focus on the results obtained by using advanced processing flows, such 3D velocity model construction using nonlinear travel-time tomography, interferometric seismic gather generation and depth imaging, as well as elastic full wave form forward modelling to help in the interpretation, analysis and uncertainty estimates.