Juan I. Sabbione

Automatic first-breaks picking: New strategies and algorithms

We have developed three methods for the automatic pickingoffirstbreaksthatcanbeusedformarine,dynamite,orvibroseisshotrecords:amodifiedCoppens’smethod,anentropy-based method, and a variogram fractal-dimension method.Thetechniquesarebasedonthefactthatthetransitionbetweennoiseandnoiseplussignalcanbeautomaticallyidentified by detecting rapid changes in a certain attribute energy ratio, entropy, or fractal dimension, which we calculate withinmovingwindowsalongtheseismictrace.Theapplication of appropriate edge-preserving smoothing operators to enhancethesetransitionsallowedustodevelopanautomated strategy that can be used to easily signal the precise location ofthefirst-arrivalonset.Furthermore,weproposeamispickcorrectingtechniquetoexploitthebenefitsofthedatapresent in the entire shot record, which allows us to adjust the traceby-trace picks and to discard picks associated with bad or dead traces. As a result, the consistency of the first-break picks is significantly improved. The methods are robust under noisy conditions, computationally efficient, and easy to apply. Results using dynamite and vibroseis field data show that accurate and consistent picks can be obtained in an automated manner even under the presence of correlated noise, badtraces,pulsechanges,andindistinctfirstbreaks.

A generalized effective anisotropic poroelastic model for periodically layered media accounting for both Biot's global and interlayer flows: Effective anisotropic poroelastic model

We present a generalized effective poroelastic model for periodically layered media in the mesoscopic scale range, which accounts for both Biot’s global and interlayer wave-induced fluid flow, as well as for the anisotropy associated with the layering. Correspondingly, it correctly predicts the existence of the fast and slow P-waves as well as quasi and pure S-waves. The proposed analytical model is validated through comparisons of the P-wave and S-wave phase velocity dispersion and attenuation characteristics with those inferred from a one-dimensional numerical solution of Biot’s poroelastic equations of motion. We also compare our model with the classical mesoscopic model of White for a range of scenarios. The results demonstrate that accounting for both wave-induced fluid flow mechanisms is essential when Biot’s global flow prevails at frequencies that are comparable or smallerwith respect to those governing interlayer flow. This is likely to be the case in media of high permeability, such as, for example, unconsolidated sediments, clean sandstones, karstic carbonates, or fractured rocks. Conversely, when interlayer flow occurs at smaller frequencies with respect to Biot’s global flow, the predictions of this model are in agreement with White’s model, which is based on quasi-static poroelasticity.