The AVO Feature Analysis Based On Two-phase Medium Theory

With the development of geophysical prospecting,idealized geological structure model can't adapt to the necessary of current exploration,how to establish a geological structure model that approach to the really structure is a hotspot of current research.The two-phase medium theory fully considers the complexity of stratum,introduce disturb of seismic wave in two-phase medium theory,it could reflect propagating situation of elastic wave in stratum,get more valuable information and provide important evidence for oil-gas exploration.This paper is about AVO(Amplitude variation with offset)forward model based on the two-phase medium theory.The application of AVO technology could know well situation of stored oil-gas and determine reservoir conditions.But traditional AVO technology is based on one-phase medium and the Zoeppritz equation,the actual reservoir is a kind of complex two-phase medium model which is composed of skeleton and fluid.Therefore,it is of great significance to establish a AVO technology based on two-phase medium.Starting from wave equation,and derive the two-phase medium AVO equation,analyze the reflection law and transmission law when the seismic wave spreads to separatrix.Research the sensitivity of oil,gas and water in two-phase medium reservoir and the influence of porosity in stratum,find out the model with high sensitivity and its' angle range,which prepare for AVO inversion.At the same time,the AVO equation of the two phase medium can degenerate into the zero offset time two-phase medium equation and Zoeppritz equation of the single-phase medium.Compare to reflection and transmission curve of two equations in condition of different angle and obtain more information.There are three main types of two-phase media model in this paper:(1)The interface of single phase medium and two-phase medium(the top interface of Reservoir);(2)The interface of two-phase medium and single phase medium(the bottom interface of Reservoir);(3)The interface of two-phase medium and two-phase medium(the interface of Reservoir);According to the different conditions,I analyze the energy distribution of the seismic wave propagating in the interface and the propagation law of the seismic wave in the two-phase medium.Based on Biot theory and BISQ model,researched a method for obtaining the parameters of reservoir of two-phase medium,discussed the relationship between fast and slow longitudinal waves in two-phase medium and their attenuation characteristics.Established a set of forward modeling of gas detection,porosity and reservoir prediction,and through the experiment,it has achieved good results,which provides reliable data support for AVO inversion of two-phase medium.In the end,An improved genetic algorithm is proposed,inversed porosity,permeability and saturation based on BISQ model,and analyzed the inversion results in detail.