Wang Yugui1, Wang Yanchun1, Wei Xiucheng3, Yang Zhiren2, Zhang Danli2
1. China University of Geoscience,Beijing City,100083,China;
2. Daqing Drilling Engineering Branch of Daqing Oilfield,Daqing City,Heilongjiang Province,163357,China;
3. Research Institute of Exploration and Development of SINOPEC,Beijing City,100083,China
Abstract：The VSPCDP transform and stack method are commonly used for non-zero offset VSP imaging.Since the method uses ray method for model building in depth domain and is on the basis of the hypothesis of layered and uniform medium and down-going first breaks,the method has following shortcomings: ①it is difficult to create accurate model in depth domain;②there is non-homogeneity in practical bed,the thicker the modeled bed is divided,the larger different to real case;③the processing method only considering down-going first breaks may appear the situation that there is non-consistent propagating direction between up-going waves and of real data.In face of these issues,the paper improved the non-zero offset VSP imaging method in three aspects: ①changing uniform layered medium model into non-uniform continuous medium model for the model above the shallowest geophone point;②changing model building in depth domain into imaging controlled by structural framework in time domain;③changing individual imaging at single survey point into joint imaging at two survey points.The improved non-zero offset VSP imaging is more reasonable in principle and easy to implement in method,and there is evident improvement in both work efficiency and imaging results.
