This case study presents the results of applying anisotropic depth migration to a resource play dataset in the Niobrara shale. For depth imaging purposes, the refraction model was integrated into the near surface velocity field. We chose to characterize the area as vertical transverse isotropy (VTI) due to low geologic dip. To constrain the anisotropy parameterization, a walkaway check-shot was acquired and a geologic frame of reference utilized to propagate the anisotropic models. A series of attributes were run on the pre-stack time migration and pre-stack depth migration results in an attempt to quantify the improvement.
Deriving anisotropic parameters in the manner presented here and applying anisotropic pre-stack depth migration have applications extending beyond just resource plays. However, by applying these technologies in this project, we show improvements to seismic data not previously seen in prestack time migration or even isotropic pre-stack depth migration.
The project successfully used a geologically constrained anisotropy modeling procedure. By providing a more representative earth velocity field, we are able to show imaging improvements in this dataset and reduce seismic to well mis-ties significantly. In addition, extensive comparisons between pre-stack time migrated data and anisotropic pre-stack depth migrated data showed a carry through of the imaging improvements to various attributes extracted from the volumes.
