The Study Of Seismic Converted-Wave Pre-Stack Depth Migration Imaging In Angle Domain

Currently, The main factors influencing the prestack depth migration include three aspects: firstly, pre-stack seismic data; secondly, the velocity model for imaging; thirdly, the selection of migration operator. In actual pre-stack imaging, Data is a prerequisite; operator or algorithm is guaranteed; The imaging velocity is the core. These three aspects are interactional. A good imaging results are primarily based on these three problems solved well. But so far, only the study of the third problem is more in-depth. While the study of the other two aspects are also existing great space for development. Meanwhile, the future direction of pre-stack depth migration should be for the high signal-to-noise, high-resolution and high-fidelity of full-wave imaging; Therefore, It has more theoretical and practical significance to carry out more extensive converted-wave imaging methods and migration velocity modeling of common imaging point gathers.Pre-stack depth migration(PSDM) requires an accurate velocity field, but the uncertainty of the velocity or layers makes it very sensitive for the PSDM velocity. Therefore, we can use PSDM method for velocity modeling, and the criterion for a correct migration velocity field is how to get a best imaging results. In the migration velocity modeling, how to build a common image gather for migration velocity analysis, in recent years,which has become a hot area of Geophysical Research. Among them, the more general is offset domain common image gathers(ODCIG) and angle domain common image gathers(ADCIG).Especially ADCIG, in recent years, is much favored by the majority of geophysicists. The ADCIG based on the wave equation is proved to be the only gathers with no illusion, which is also considered to be the most reasonable gathers.Firstly, This paper gets the one-way wave preserved-amplitude decomposition from the whole way acoustic wave equation based on the more stringent decoupling theory, and gets more intuitive and more efficient one-way wave equation which is directly continuating to the pressure wavefield component. Then the author makes use of decoupling one-way wave operator deducing the single square root(SSR) and the double square root(DSR) amplitude-preserved continuation operator. And studied PP and PSV wave pre-stack depth migration using SSR operator and DSR operator respectively. Then, in the CMP domain, Reverse continuating to the pressure wavefield component using double square root operator, and then get common imaging in offset domain, After that, making the offset information mapped to the angle domain In the frequency-wavenumber domain, then get a ADCIG; Pointing out that the extraction process of ADCIG is actually transformed seismic data offset information. In essence, it still is a reflexion to multi-offset seismic data information. At the same time, the paper use the MPI parallel algorithm to solve the time-consuming or the low computational efficiency in pre-stack migration. It makes Pre-stack migration possible for the actual seismic exploration. Finally, the paper Studied the sensitivity of ODCIG and ADCIG to speed error, Noted that ADCIG is a more suitable gathers for velocity analysis and AVO /AVA analysis. When the velocity is correct, ADCIG event is a flattened gather; When the migration velocity is small, ADCIG event is upturned, the relationship between ADCIG and imaging depth is an oval; when the migration velocity is too large, ADCIG event is recurved, the relationship between ADCIG and imaging depth is a hyperbolic.