Abstract:At present, there are mainly two categories of fracture prediction methods. The first type is based on the amplitude or attributes (such as frequency and attenuation) derived from the amplitude of azimuth seismic data. It can only provide the comprehensive response information of the strata on both sides of the interface and fails to determine the fracture information of the overlying or underlying strata. The second type obtains the elastic parameters with the help of azimuthal AVO prestack seismic inversion, which can directly achieve the fracture information of target strata. However, the dimension of the parameters to be inverted is high, and the anisotropic parameter is much smaller than the elastic parameter, with the inversion stability needing to be improved. In response, this paper proposes a fracture prediction method based on the Fourier series of azimuthal elastic impedance. Firstly, the azimuthal elastic impedance equation is derived on the basis of the Rüger’s approximation of the azimuthal AVO reflection coefficient. The interface information of a fractured medium is transformed into the elastic information of the formation. The difference in azimuthal elastic impedance reflects the anisotropy of the formation. Secondly, the azimuthal elastic impedance equation is expanded by Fourier series to obtain the second-order Fourier coefficient . Finally, the normal direction of fracture is obtained through the cross-correlation between azimuthal elastic impedance and cosine function. The model test shows that the fracture prediction method based on the Fourier series expansion of azimuthal elastic impedance can well predict the development and normal direction of fracture with high accuracy and strong noise resistance. The performance on actual data indicates that the fracture prediction results are consistent with the imaging logging results, which proves that the method has high accuracy.
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