Interval anisotropic parameter estimation using velocity-independent layer stripping

Moveout analysis of long-spread P-wave data is widely used to estimate the key time-processing parameter η in layered VTI (transversely isotropic with a vertical symmetry axis) media. Inversion for interval η values, however, suffers from instability caused by the tradeoff between the effective moveout parameters and by the subsequent error amplification during Dix-type layer stripping. Here, we propose an alternative approach to interval parameter estimation based on the velocityindependent layer-stripping (VILS) method of Dewangan and Tsvankin (2006). This method makes it possible to compute the interval moveout in a layer of interest without knowledge of the medium parameters in the overburden. Thus, the layer stripping of moveout parameters in the conventional method is replaced by the much more stable stripping of reflection traveltimes. We also develop the 3D version of the layer-stripping method and apply it to interval parameter estimation for orthorhombic media using wide-azimuth P-wave data. The superior accuracy and stability of our algorithm is illustrated on noise-contaminated ray-traced synthetic data for typical layered VTI and orthorhombic models. The algorithm is also tested on wide-azimuth P-wave reflection data recorded above a fractured reservoir at Rulison field in Colorado. The interval η values estimated by VILS are more plausible and stable than those obtained by the Dix-type method.