TESTING OF AN OPTIMIZATION ALGORITHM FOR AVAZ INVERSION ON SYNTHETIC DATASET

In the paper, we study an optimization algorithm for a nonlinear AVAZ inversion of PP reflections from an anisotropic media. The algorithm is based on the exact formulas for PP wave reflection coefficient for an anisotropic HTI medium and could be applied in the case of strong-contrast boundary and various anisotropy degree. Algorithm testing on synthetic dataset for radial survey system shows that estimation of anisotropy parameters γ , δ and HTI medium symmetry axis is robust in the case of signal to noise ratio ≥ 5. For estimation of parameter ε far offset data is needed.

Study of the influence of anisotropy parameters on reflection coefficients from a boundary between two azimuthally anisotropic media

The paper considers an algorithm for calculating reflection coefficients from boundary between two HTI media. Analysis of the presence of anisotropy above and below the target boundary, as well as variations in the parameters of HTI media, was done. Interpretation of reflection data from the boundary between two HTI media with neglect of anisotropy above or below potentially leads to significant errors in estimation of symmetry axes directions, and hence fracturing orientation. Overestimation/underestimation of an elastic parameter in the overlying HTI medium could lead to a corresponding overestimation/underestimation of similar parameter in the underlying target layer in the result of AVAZ inversion. Furthermore, among the anisotropy parameters Thomsen parameter γ has most significant influence on the reflection coefficients dependences. Thus, the parameter γ could be used foremost as a result of the AVAZ inversion.

Study of near–surface azimuthal anisotropy with refracted waves

The method of refracted waves is often used for shallow investigations. Moreover, a rather limited observation system in the form of unidirectional profiles is often used. In our work, we selected an object of study with a known strong anisotropy of the upper part of the section. Field work and data processing were carried out. The results show strong anisotropy of one of the layers of the medium, the azimuthal anisotropy of which led to the fact that the refraction on its top ceases to appear in the first arrivals, for the direction of the profile along the axis of symmetry of the corresponding HTI medium.

DETERMINATION OF AZIMUTHAL ANISOTROPIC MEDIA ELASTIC PARAMETERS FROM MULTIWAVE AVOA DATA BY NONLINEAR OPTIMIZATION METHOD

In this paper, we investigate optimization algorithm of joint nonlinear AVOA inversion of PP+PS reflections in anisotropic media. Algorithm is based on the exact solution for PP and PS waves reflection coefficients in anisotropic HTI medium. The PP and PS wave’s reflections from the top of the anisotropic layer are examined. We use synthetic seismograms generated by ray method for the algorithm testing. We show that joint compressional and converted wave’s inversion allows increasing the robustness of the method and the accuracy of medium-parameter estimates. Coefficients of anisotropy are determined with better accuracy if signal-to-noise ratio is bigger than 5 for PP wave and bigger than 2 for PS wave.

OPTIMIZATION ALGORITHM ACCURACY AND STABILITY STUDY OF AVOA INVERSION OF PP+PS REFLECTIONS IN AZIMUTHALLY ANISOTROPIC MEDIA

The article investigates the accuracy and stability of the optimization algorithm for joint nonlinear AVOA inversion of PP+PS reflections in an anisotropic HTI medium. Algorithm was tested using synthetic seismograms. The analysis of objective functions is performed in order to study the sensitivity of the method to the determination of different parameters of the anisotropic model. Using two types of waves significantly increases the noise robustness of the method and the accuracy of all parameters estimation.