Study On Fracture Prediction Using Narrow-azimuth Seismic Data

Petroleum is one of the most important components in the world energy structure,and ensuring oil production is of great significance to national security and development.With the advance of hydrocarbon exploration and development,the proven reserves of fractured oil and gas reservoirs continue to increase in China,and oil and gas exploration of fractured reservoirs has become the key to ensure oil and gas productivity.Azimuthal anisotropy of the medium is related to fractures.Studies on azimuthal anisotropy using azimuth seismic data can resolve the fracture distributions in the formation,which further helps to refine the locations of reservoirs.However,due to the limit of geographical conditions and economic constraints,seismic data are generally acquired in a narrow-azimuth geometry.On the other hand,conventional methods on anisotropy are developed based on wide-azimuth seismic data,and thus are not applicable to narrow-azimuth seismic data.Therefore,the research on fracture predictions characterized by azimuthal anisotropy is carried out in this paper using narrow-azimuth seismic data.This study is based on the HTI medium,in which small-angle incidence approximation and weak anisotropy conditions are applied to simplify Rüger approximation equation and obtain a three-parameter approximation formula that contains the anisotropic combination parameters for characterizing the fracture density.Based on the three-parameter approximation formula,an inversion method for solving anisotropic parameters is established,and the stability of the inversion method for the finite azimuth condition is also analyzed.In order to make up for the problems caused by the lack of azimuth,this study further develops and utilizes the dispersion information in the seismic data,and constructs the dispersion attributes of the anisotropic combination parameters based on the frequency variation theory of seismic signals.Furthermore,a method for inversion of dispersion properties based on the three-parameter approximation formula is established,which uses Marr wavelet frequency division to obtain the reflection coefficient in frequency domain,and then use the frequency division information to invert the anisotropic dispersion attributes that characterizes the fracture densityFinally,the study applied the method to synthetic narrow-azimuth seismic data,and the inversion results based on the three-parameter approximation were compared with the inversion results by Rüger equation.Reasonable match between the two inversion results proves that the three parameters approximation formula is feasible for the anisotropic parameter inversion.Furthermore,the inversion of the dispersion attributes of anisotropic parameters is carried out.The results show that the dispersion attributes of anisotropic combination parameters have better fracture indication and can be used to predict the fracture density distribution on narrowazimuth seismic data.