Application of 3D VSP's to Tight Gas Reservoir Characterization

Abstract

Exploration and development of tight-gas sandstone reservoirs relies heavily on understanding the distribution of sandstone bodies in the subsurface. Shear-wave sourced 3D vertical seismic profiling (VSP) data are used for sandstone detection and fractured interval delineation. Anisotropic Kirchhoff 3D prestack depth migration was applied to the shear-wave reflection data. A geologically-constrained migration-velocity model was created by integrating the results from the virtual source method, well logs, interval velocity derived from surface seismic and the Dix-differentiation of the fast and slow shear-wave NMO ellipses. The resulting common image gathers (CIG) are flat, indicating that the reflection events can be stacked reliably. The depth migrated images tie with the well logs and the surface seismic data. The VSP images show subtle stratigraphic features involving sandstone intervals in the Williams Fork Formation and pinchouts in the coal beds within the Cameo Coal interval. Structural features, especially faults, previously unnoticed on surface seismic data are now clearly visible. The shear-wave VSP data can now be used as a complementary dataset to other commonly acquired data such as surface seismic, well logs and core data and microseismic information to improve reservoir characterization.