The Forward And Inverse Of Q Value Using Prestack CMP Gather 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. There has energy degradation in the process of seismic wave propagation, which will definitely affect the resolution of seismic exploration. There are various ways to improve the resolution, inverse Q filtering is one of the more commonly used methods. The key to effective inverse Q filtering is clarifying quality factor of the layer.This paper has studied the forward and inverse of Q based on the analysis of attenuation characteristics and influence factors. The specific contents are as follows:(1) Expounded the non-elastic attenuation mechanism of formation, physical meaning and impact factors of the quality factor Q, described the research status of seismic wave attenuation methods at home and abroad, reviewed the traditional method about estimating Q values(2) Introduced the pre-stack inversion method of CMP quality factor raised by Changjun Zhang in 2002 and absorption equation launched by Liu Yang, Xiucheng Wei in 2009, have Programmed to achieve the forward and inverse calculation of Q values in this method(3) Author carried out forward calculation to a variety of simple geological models, and generated synthetic seismograms of layered attenuation models, which is fit for the decadent layered geological model in the case of normal incidence. On the basis of the above calculation author also compared with the fadeless seismic profiles, and revealed the reduction of frequency and energy of the seismic wave caused by attenuation characteristics.(4) Author carried out inversion calculation to forward model, and analysed the inversion results of this method under different model parameters. In the paper, author reached following conclusions:â‘ Accuracy of Q value inversion is directly affected by the selection precision of peak frequency;â‘¡Inversion results of low-speed sandwich are better than high-speed when there are low or high-speed sandwich between layers.â‘¢When there is strong attenuation layer, the inversion accuracy of layers under this layer are seriously affected by thickness of this layer.â‘£Use the near-offset shallow data to calculate sub-wave frequency when it is calculated. (5) In the process of dealing with the actual data, author applied this method to estimate the Q value, and made inverse Q filter based on the Q value, at last achieved good results, testifying the practicality and feasibility of the method.(6) Finally author analyzed and summarized the advantages and disadvantages and application conditions of layer stripping method, proposed mentality and direction to make this method better.