Shale Rock Physical Response And AVO Technique

With the continuous development of world economy,the demand of oil and gasresources grows, and the development of renewable alternative energy is slowly, andthe unconventional reservoir of oil and gas resources was paid more attention. Thestudy of shale rock physics model has very important significance, because shale oiland gas reservoir occupies a large proportion in unconventional oil and gas reservoirs,and the results may provide a theoretical basis for seismic inversion.It is started to study the model of shale rock physics in the area of seismicexploration. There are two kinds of this models: one is the model of organic-richshale whose pore is filled with kerogen(solid organic matter),oil,water and so on. Theother one is model of shale with horizontal bedding-fracture. And this kind of shale isfracture-rich with some microfracture which makes up the channel for hydrocarbonflowing. Both of the two kind of models can describe the VTI shale.The relationship of reflection coefficient with the content of kerogen, angle ofincidence,and the formation thickness on organic-rich shale has been discussed. Andthe effect of frequency is added to calculate the reflection coefficient of organic-richshale model with different thickness using propagation-matrix method in this paper.Then the variation of frequency-variable reflection coefficient with angle ofincidence is obtained to get the synthetic seismogram with adding the influence ofwavelet.The shale model of horizontal bedding joint is applying existing Hudsonfractured model and Schoenberg fractured model to shale media, which thebackground rock is the shale rock. Through the transmission matrix algorithm, wecalculate layer reflection coefficient of the horizontal bedding joint shale model,getting the relationship of frequency dependent reflection coefficient under differentcrack density change with incident Angle, then adding the wavelet to get theinfluence of reflection wave of seismic synthetic record.Results show that the seismic reflection characteristics of kerogen content andfracture density is very sensitive. For the rich organic matter model of the shale, layerthickness increase will make the frequency of reflection coefficient frequency perioddecreases and kerogen content increase will make rich organic shale speed reduce,which make the formation of the wave impedance difference larger, so the reflectedwave amplitude increase. Fracture density increase, making the shale vertical velocity decrease very obvious, leading to the anisotropy of shale rock, wave impedancedifference, reflected wave amplitude increasing.This article also conducted some exploratory research: there may be somecracks in the shale, that makes the shale have a low permeability, and increasedpermeability lead to seismic wave velocity decreases; The fluid, injected into thecrack or pore,will make effective stress generated by incident wave decreases, it willlead to seismic wave velocity decreases.