Estimation Of Quality Factors From Viscoelastic Medium

Traveling through the earth media, seismic waves will experience attenuation and dispersion as a result of the anelasticity and heterogeneity of the medium. Understanding, estimating and compensating of the absorption of seismic waves are important to improve the resolution of seismic images, better interpret the effects of AVO, and under favorable conditions it can also be used to predict the existence of oil and gas.This paper mainly studied three parts:(a) the mechanism analysis about the factors that can influence the seismic wave attenuation;(b) The propagation law of seismic wave in viscoelastic medium and its influence on the absorption and attenuation of seismic energy;(c) The research of methods of extracting the quality factor Q based on the theory of time-frequency analysis.In the study of estimating the quality factor by using time-frequency analysis method, this article is based on the absorption attenuation model to extract the Q value proposed by White R.E.(1992).With the influence of attenuation effect, the seismic pulse spectrum changes a lot: its spread decreases constantly; its amplitude peaks move to low frequency; its band narrows gradually. This paper is mainly based on the thought of Q value from peak frequency by Zhang and Ulrych(2002). At the same time, the Q value analysis method by Wang Anghua is used for reference. In this paper, we calculate and deduce the relationships between main frequency, peak frequency and Q value in the generalized S transform spectrum. Then it has been used in the generalized S spectrum peak frequency in the post-stack profile to calculate the Q value. By this way, it improves the computational efficiency and precision of the Q value. This method is different from the past simple method to calculate T- Q of the interpolation points to get the Q value of profile. It is gained directly from seismic profile inversion method. It is better to get the useful information of strata and to make good preparation for the subsequent analysis of the reservoir.