Research On Features Of AVO Forward Modeling And Attribute Analysis In Complex Media

AVO technology is a kind of technical method which is widely used in the world by people at present,it is a kind of seismic exploration technology of geophysical exploration methods,this technique is mainly used to identify oil and gas or the identification of special lithology in practical exploration.Up to 2017,AVO technology has been developed for nearly one hundred years and has formed a very rich and rigorous theoretical system.AVO theory is based on the Zoeppritz equation.When a plane wave incident to the horizontal interface,there will be reflected longitudinal wave,transmitted longitudinal wave,reflected wave and transmission wave on both sides of the interface.In order to describe the energy relationship between these waves,Zoeppritz introduced the Zoeppritz equations in 1919 according to Snell's law and Newton's third law.But the Zoeppritz equation is very complex,and the relationship between the parameters is not clear,so it's not suitable for practical application and theoretical research,so many scholars have simplified the Zoeppritz equation from different aspects in order to meet the needs of the people.The main task of AVO forward modeling is to study the variation of reflection amplitude with offset in different medium.Based on the AVO forward modeling of different types of gas bearing sandstone,we can obtain the AVO response characteristics of some specific formations,such as some kind of the oil and gas reservoir's amplitude of the reflected wave are increase with the increase of the incident angle,and in the synthetic seismic traces will show a "bright spot" phenomenon,In this way,we can search for oil and gas reservoirs based on AVO forward modeling.Firstly,this paper introduces the development history and research status of AVO technology,Then we introduce the basic principle of AVO technology,then deducts the complete Zoeppritz equation and introduces several Zoeppritz approximate equations,then analysis their application conditions,then the Zoeppritz approximation equation in VTI medium and viscoelastic medium are introduced.Taking Shuey and Hillterman equation as an example,we analysis the physical meaning of Zeppritz approximate equation.Then we introduce the AVO forward method of numerical simulation of seismic wave field based on wave equation and the principle of it's algorithm.Then we used this method to simulate the AVO characteristics of four kinds of gas bearing sandstone,then we analyzed the effects of fluid composition,reservoir thickness,velocities of P-wave and S-wave,density,anisotropy of medium,azimuth,porosity and viscoelasticity on AVO response.Then this paper introduces the AVO attribute analysis technology,introduces the P,G,P+G,P*G,P-G,G/P and other commonly used AVO attributes,it also introduced the application of Shuey approximate formula in AVO attribute analysis,then we introduced the AVO attribute cross plot technique,and we established 25 gas bearing sandstone models and25 water bearing sandstone models,and by using Shuey formula,we extracted P,G,P+G,P*G,P-G,G/P and other attributes,drew some AVO attribute crossplots,described the application of AVO attribute cross plot technique in identification of oil and gas layers.