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 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 velocity-independent layer-stripping method of Dewangan & 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. Then the interval traveltimes are inverted for the normal-moveout velocity (Vnmo) and η using the single-layer nonhyperbolic moveout equation. Thus, the layer stripping of η 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 ray-traced synthetic data for typical layered VTI and orthorhombic models. Even small correlated noise in reflection traveltimes produces substantial distortions in the effective η, and for some models, even in the effective Vnmo. As a result, the inter val η values estimated by the conventional Dix-type method may be highly inaccurate. In contrast, the output of our layer-stripping algorithm proves to be insensitive to mild correlated traveltime errors. The algorithm is also tested on wide-azimuth P-wave reflection data recorded above a fractured reservoir at Rulison field in Colorado. The interval moveout parameters estimated by the velocity-independent layer stripping in the shale layer above the reservoir are more plausible and stable than those obtained by the Dix-type method.
Non‐hyperbolic moveout inversion of wide‐azimuth P‐wave data for orthorhombic media
The azimuthally varying non‐hyperbolic moveout of P‐waves in orthorhombic media can provide valuable information for characterization of fractured reservoirs and seismic processing. Here, we present a technique to invert long‐spread, wide‐azimuth P‐wave data for the orientation of the vertical symmetry planes and five key moveout parameters: the symmetry‐plane NMO velocities, V(1)nmo and V(2)nmo, and the anellipticity parameters, η(1), η(2) and η(3). The inversion algorithm is based on a coherence operator that computes the semblance for the full range of offsets and azimuths using a generalized version of the Alkhalifah–Tsvankin non‐hyperbolic moveout equation.
Fast seismic data compression based on high-efficiency SPIHT
Based on the set positioning in hierarchical tree (SPIHT) algorithm, fast seismic data compression based on the high-efficiency SPIHT (HESPIHT) algorithm is presented. To verify the validity of the algorithm, 10 seismic cross-sections are selected for the experiment. The result shows that the algorithm can reserve the quality of data better, meanwhile improving the efficiency of encoding and decoding.