Sonic-derived TI anisotropy as a guide for seismic velocity model building

Abstract

While accurate velocity models are critical for seismic images representative of the subsurface, the process of determining the correct velocity model is non-unique. Seismic images may therefore come with significant uncertainty, especially in fields with complex structure in combination with a complex velocity field. In turn, this uncertainty leads to wells missing their targets as well as increased drilling risks. Borehole sonic-derived anisotropy magnitudes may provide constraints to the seismic velocity model, but the applicability of sonic-derived anisotropy to surface seismic data is unclear. In this paper, the consistency between a sonic-derived anisotropic velocity model and surface seismic data is analyzed by comparing NMO corrections on basis of a seismic-only model versus a seismic model guided by sonic-derived anisotropy. For the complex seismic dataset presented in the examples it is observed how (unlike the sonic-guided model) the seismic-only model is not able to flatten the gathers at far offsets. The process of deriving TI parameters from borehole sonic data is relatively efficient (compared to the seismic equivalent), and their use as a guide during the construction of the seismic velocity model results in subsurface images that can be established with greater confidence.