Abstract:

In the “dual complex” area of Xindianzi, Yongchuan, all the reasons that the near surface factors vary greatly, the structure is complex, and the signal-to-noise ratio of data is low make the accurate imaging difficult. During the shale gas exploration and development, there are some problems of Xindianzi such as unclear anticline structure, inaccurate imaging of local small faults, and inconsistency of horizontal well design trajectory with actual drilling. The conventional grid tomography inversion method has poor applicability in velocity modeling of low signal-to-noise ratio area. It is difficult not only to obtain the quasi shallow velocity and eliminate the influence of complex near surface on imaging, but also to realize effective data driving in the middle and deep layers and update the velocity accurately in the middle and deep layers. In order to solve the problem of depth domain modeling in “dual complex” area, full offset first break tomography inversion is used to obtain near surface velocity, then the appropriate interface is selected to fuse the models of shallow and medium depth. In the iterative process of grid tomography, the constraints on velocity by the construction model can realize the corresponding between low-frequency velocity and structural distribution, and get high-frequency convergence. The application results show that the joint application of shallow, medium and deep fusion modeling and structural constraint grid tomography technology make up for the shortcomings of the conventional methods, the resulting final velocity field is more accurate, and the imaging of the “dual complex” area is obviously improved. The results strongly support the exploration and development of this area.

Key words: dual complexity, velocity modeling, tomographic inversion, velocity fusion, structural constraint, gaussian beam depth migration