Alimzhan Zhubayev

Contrasting behavior between dispersive seismic velocity and attenuation: Advantages in subsoil characterization

A careful look into the pertinent models of poroelasticity reveals that in water-saturated sediments or soils, the seismic (P and S wave) velocity dispersion and attenuation in the low field-seismic frequency band (20-200 Hz) have a contrasting behavior in the porosity-permeability domain. Taking advantage of this nearly orthogonal behavior, a new approach has been proposed, which leads to unique estimates of both porosity and permeability simultaneously. Through realistic numerical tests, the effect of maximum frequency content in data and the integration of P and S waves on the accuracy and robustness of the estimates are demonstrated.

Physics of shear-wave intrinsic dispersion and estimation of in situ soil properties: a synthetic VSP appraisal

ABSTRACT Estimates of in situ porosity and permeability in saturated soils are important in various disciplines. In this research, a recently proposed concept for quantitative integration of dispersive seismic velocity and attenuation in soft soils, based on the underlying physics, is tested on a realistic synthetic shear‐wave (S‐wave) vertical seismic profiling (VSP) dataset. The effects of error in the determination of layer‐specific dispersive velocity and attenuation from VSP data without and with noise, as well as those of error in the used poroelasticity model, on the estimated values of porosity and permeability are investigated. A methodology involving extraction of layer‐specific intrinsic dispersion from VSP data and enhancement of robustness and reliability through use of multiple receivers within the thickness of a given layer, in combination with source stacking, is presented. For the assumed frequency band (50–140 Hz) for S‐wave data, stable values of both porosity and permeability can be obtained for all but a very low‐permeability clayey layer. The results show that if the model error is not large, then both porosity and permeability can be estimated quite accurately even when the data are rather noisy. However, when the model used is grossly inaccurate and there is large noise in the data and hence a large error in the estimated dispersion, then though the absolute error in porosity is still within 2–3%, the permeability can be off by an order of magnitude. In general, in this approach, if the poroelasticity model is so chosen that it explains reasonably well the observed dispersion, then the estimates of in situ porosity and permeability should both be quite accurate.

Physics‐based integration of shear wave dispersion properties for soil property estimation: Laboratory investigation

Laboratory experiments have been conducted to measure shear wave velocity dispersion and attenuation in watersaturated, unconsolidated sand. The goal is to exmine the validity of a new methodology (Zhubayev and Ghose, 2010), which allows one to estimate simultaneously in-situ porosity and permeability from frequency-dependent shear wave velocity and attenuation measured at field seismic frequency band and using the poroelasticity theory. The theory to be used is data-driven. For our laboratory data, we have used the Stoll and Bryan (1970) formulation which works well for a large variety of soil types. Our laboratory measurements of shear wave velocity and attenuation indicate significant dispersion at 2-8 kHz frequency range. In this paper we present our results on laboratory dataset and discuus the potential of the new approach.