Boris Gurevich, Professor at Curtin U. and CSIRO (Australia) presents "Estimation of seismic attenuation by wavefield inversion of VSP data."
Knowledge of seismic Q is important for imaging and inversion, and can also provide additional information about subsurface rocks. Commonly, Q-factors are estimated from vertical seismic profile (VSP) data by the analysis of the evolution of the frrquency content of direct arrivals. Since effects of fine layering, i.e. 1D scattering at stratigraphic boundaries, and other interference are not taken into account, obtained Q-factors have large uncertainty. We propose to quantify interval Q-factors by wavefield inversion of VSP data using a high-resolution elastic model from well logs (resolution of 1.5m or less). Forward simulation over a thin-layered model allows one to tackle overlapping of direct arrivals with short-path multiples and primary reflections. A synthetic test shows high accuracy and good vertical resolution of Q estimates. Application to field data shows results consistent with other estimates, but with potentially higher vertical resolution.
ASSUMED PRIOR KNOWLEDGE
General geophysical principles, including basic VSP and inversion principles.