The Study Of Multi-component VSP/RVSP Seismic Forward Modeling

Oil exploration has come to the stage of the complex structure exploration and lithologic oil and gas exploration. The rate of the successful convitional exploration decreases gradually. So the application of the well seismic technology becomes more widely. Vertical seismic profile (VSP) technology and it's developed RVSP technology have been widely used as the well seismic technology. In order to provide reasonable technical guidance for the field VSP/RVSP acquisition system and the necessary theoretical support for the processing and interpretation of field VSP/RVSP seismic data, we must clarify the seismic wave propagation in the subsurface of the VSP/RVSP observation system. VSP/RVSP simulation is the most effective means to understand the wave field propagation in the underground media.In the scalar wave numerical simulation, high order finite difference algorithm is used to implement the numerical simulation of wave equation in the 3D isotropic medium. By numerical dispersion analysis, we eliminate the impact of the numerical dispersion of space and time; at the same time, by constructing the absorbing boundary of perfectly matched layer (PML) for the scalar wave, we solve the key problem of the numerical simulation—the artificial boundary reflection effect. Then, the scalar wave VSP/RVSP order finite difference algorithm is used to make a numerical simulation on the theoretical models and real geophysical model. By analyzing the simulated wave field snapshots and shot records, we recognize the P wave propagation characteristics in various structures, which guides the establishment of the actual observation system.In the elastic wave numerical simulation, the multi-component VSP/RVSP high order finite difference algorithm with P-wave and S-wave complete separated is achieved by derivation of the P-wave and S-wave completely decoupled time domain order finite difference scheme. And, the artificial boundary effects are eliminated by constructing elastic PML absorbing boundary. The characteristics of different sources generating seismic waves are analysised by simulating effects of different sources loading methods on wave field. The snapshots and shot records of the multi-component full-wave field, pure P wave field and pure S wave field. Then we obtain the propagation of the elastic wave in multi-component VSP / RVSP observation system.The migration of the non-zero offset VSP data is one of the key technologies to process non-zero offset VSP data. In the procedue of non-zero offset VSP data migration, firstly, we use f-k transform to separate the upgoing and downgoing waves according to the different characteristics of waves. Then, according to the fact that the shot points on the ground are more than the detectors in the well in the VSP observing system, common receiving point gathers are distilled from VSP data with the reciprocity principle of seismic wave feilde. At last, the prestack migration of one-way wave operator is implemented with common receiving point gathers. One-way wave operator wavefield extrapolation method is good at amplitude preserving, and can adapt to strong variation of the lateral velocity. one-way wave operator wavefield extrapolation method can be well applied to the migration of the VSP common receiving point gathers seismic data.The method is also applied with the the RVSP record's depth migration.