The Forward And Inverse Of Q Value Using Zero-offset VSP Data

The energy attenuation of propagation medium shows the nonelastic property during waves propagating in it. Many tests have confirmed that the attenuation characteristics is sensitive to the elastic and fluid property of reservoirs. Generally, Q value, short for Quality factor, is used to show the intrinsic attenuation. On the other hand, VSP, which can thoroughly show the basic propagation characteristic, directly receive seismic waves in the different depthes to help people understand the reflection and transmittion, is regarded as the only way to reply the attenuation from seismic datas.This paper has studied the forward and inverse of Q basing on the analysis of attenuation characteristics and influence factors. Considering the reflection and refraction, the synthetic seismograms of layered attenuation models are generated basing on Ganley's theory, which is fit for the normal incident. Compared with the unattenuation records, the decreases of energy and frequency display the characteristic of the unelastic models. Secondly, with the discussion on the theory of CFS, short for Centroid Frequency Shift method, the paper inverses the Q value for the forward zero-offset VSP model and compares the results with amplitude attenuation method and the ratio of frequency spectrum method. It shows that CFS is superior in the recognition of thin layers, the separation of multi-layers, the anti-disturbance of interfaces, the adaptation of shot's location. It also discusses the influence of the frequency band and the choice of velocity used to inverse. Finally, the processing of two field datas reveals its practicality and feasibility.