| As the exploration and development potential of China’s structural oil and gas reservoirs is exhausted,lithologic oil and gas reservoirs become the main target of exploration and development.Most lithologic oil and gas reservoirs in China have the typical characteristics of thin interbed sedimentation,which present small sedimentary scale and thin single-layer thickness that is often lower than the longitudinal resolution of seismic exploration.The traditional seismic exploration methods are no longer suitable for thin interbedded strata.Based on the Walkaway VSP data of TP327 well in Tuofutai area,this paper proposes a set of high-precision seismic processing and interpretation procedures for thin interbedded strata.VSP seismic data has high resolution,and it can effectively image some small structures and sedimentary units underground,which is beneficial to improve the accuracy of thin interbedded reservoir prediction.At present,however,there is still no complete industrial system for the processing of VSP seismic data,because VSP seismic adopts well-in-well observation mode,which leads to the asymmetry of their paths both horizontally and vertically,and then the time-distance curves no longer have hyperbolic characteristics.The methods of velocity analysis in ground seismic are no longer applicable to VSP seismic data.Based on the VSP special observation method,the paths of reflection wave are extended to the same datum as the shot point,which accords with the path characteristic of ground seismic.By VSP-CIG process and inverse hyperbolic correction,the VSP dataset is converted into the CIG dataset of ground seismic.In the imaging process,anisotropic correction is introduced to improve the imaging accuracy greatly.On the basis of high-precision processing of VSP data,the joint anisotropic AVO inversion technique of PP-and PS-waves for thin interbedded reservoirs is developed.Based on the reflection coefficient equations of the VTI media proposed by Rüger,this paper uses the least square method to construct the objective function in the inversion,and the Gaussian-Newton iteration method is used to make the objective function converge quickly.In order to reduce the multi-solution problems of the inversion,the model constraints are appropriately added in the inversion process.Finally,this method can be used to retrieve the velocity of P-and S-wave velocities,densities of both single sandstone and single mudstone formations and sand-to-ground ratios.The method is applied to TP327 area in Tuofutai,and the P-and S-wave velocities and densities of sand and mudstone formations in Carboniferous-Permian clastic reservoir are obtained. |
