AVO Inversion Based On Prestack Migration Data

Considering the currently developing requirement of exploring technology in complexstructure areas, based on the understanding and recognition of AVO background, history, stateof art and developing trends, and by closely combining with the practical production, this papermainly researches the AVO inversion based on prestack migration to acquire multiple AVOattribute parameters which reveal the variable density of lithology or pore fluid. At the sametime, this paper also probes into the method of evaluating and selecting the above invertedvarious attributes, and the method of determining and interpreting AVO anomaly using theintegrated analysis of selected multiple AVO attributes.At first this paper introduces the basic principles of AVO technology, and then points outthe critical aspects of AVO preprocessing on the premise of analyzing the factors that affect theprestack seismic reflection amplitude variation versus offset, and introduces the prestack depthmigration technology into the AVO preprocessing flow by emphasizing the importantsignificance of prestack migration in the AVO study of complex structure areas, which greatlyimproves the resolution and signal-to-noise ratio of seismic data and thus can further providecomparable high-quality prestack seismic data for the AVO study. On the basis of the foregoingstudy, this paper detailedly discusses the basic principles and achieving steps of the method ofweighted-stacking AVO inversion which makes use of the different approximate formulae ofZoeppritz equations to invert various AVO attributes. At last this paper presents the BESevaluating method which is used to evaluate and select the inverted various AVO attributes, andalso puts forward a multi-attribute AVO analysis approach by integrating along-horizonattribute slice analysis, 3-D visualization technique, AVO cross-plotting analysis, attributeprofile analysis and AVO character curve analysis techniques.This paper takes the seismic data from some 3-D seismic survey of the middle andsourthern part of Wuerxun Depression in Hailaer Basin of Inner Mongolia Municipality as anexample of complex structure area, and apply the above proposed research method to processthe seismic data. Firstly, the seismic data are preprocessed according to the purpose of AVOstudy, among which a point need to especially point out is the 3-D prestack Kirchhoff depthmigration processing technique is used and thus the quatity of the seismic data are improved.Then using the common reflection point (CRP) gathers and the interval velocity model acquiredfrom prestack Kirchhoff depth migration as the basic data of AVO inversion, by utilizing theweighted-stacking AVO inversion method, the author acquires 15 attributes which include AVOintercept, gradient, Poisson's ratio reflectivity, fluid factor, compression wave velocityreflectivity, shear wave velocity reflectivity and so on. According to the proposed researchthought, the 15 attributes are evaluated making use of the BES evaluating method and 14attributes of them are selected as available attributes. At last based on the selected 14 AVOattributes, the author primarily determines two AVO anomalies in the research area usingalong-horizon attribute slice technique and 3-D visualization technique, and then furtherdemonstrates and reasonably interpret the two AVO anomalies using cross-plotting analysis,attribute profile analysis and AVO character curve analysis techniques.The processing and analysis of the practical seismid data indicate that the probing researchmethod which is proposed in this paper for the purpose of applying AVO technique to thecomplex structure areas is helpful in the aspects of improving the AVO analysis effects incomplex structure areas, and thus it plays a certain positive role in the AVO study of complexstructure areas.