The Ray Tracing Forward Modeling Of VSP In Deviated Well

VSP is a seismic survey technology in wells.Compared with surface seismic technology,VSP has a higher S/N ratio and resolution,and its waves'motive and dynamic characteristics are more conspicuous.VSP technology provides a most directly corresponding relationship between underground stratum structures and surface survey parameters.It can provide precise time-depth conversion and velocity model for processing and interpretation of surface seismic data.It can exactly identify geologic stratum of seismic reflection and improve the interpretation effect of surface seismic data.We can even do a research on lithology and physical property of reservoir by use of VSP data.thus,VSP is a promising seismic survey technology. With the deviated well VSP technology development, the devited well VSP model technology has become of concern,the VSP model technology has become an important means for the vertical seismic method. Deviated well VSP model technology can help deviated well VSP design in the field and select the best acquisition parameters; it can help identify the characteristics of wave field of deviated well VSP, choose the suitable method for the Separation of wave field and a processing parameters; It can also be used to test devited well VSP to deal with new methods and the final interpretation of results, so it is very necessary to the VSP forward simulation for the deviated well.This paper analyzes the basic characteristics of VSP, and then explains the type and characteristics of seismic wave on the basis of VSP, finally detailed studies the VSP observation methods,on based on this selects a suitable observation system for the seismic research. The paper used iterative ray-tracing method to perform VSP forward for the two-dimensional and three-dimensional model, and further studied the kinematical characteristics of seismic waves. At the same time,considering the interface energy distribution, so that the incident angle between interfaces and rays is firstly calculated, then by substitution of the angle obtained from above analysis into the Zeoppritz, the corresponding reflection coefficient and transmission coefficient can be obtained. Finally, the reflection coefficient is convolved with the theoretical seismicwavelet to synthesis the theoretical VSP data.From the eikonal equation of ray theory, This paper completed the two-dimensional and three-dimensional deviated well VSP forward two points ray tracing methods,processing and calculation procedures, formd a specific forward algorithm, achieved the deviated well VSP theoretical model of ray tracing path, while using ray tracing rays from the parameters, taking into account the seismic wave-ray energy characteristics. It tests the validity of the method through multiple model spreadsheet. The forward simulats the single-layer, multi-layered reflection wave, variable offset the direct wave, various waves of the forward model in 2D and 3D deviated well.By the forward modeling, we not only see the direct wave intuitive and the reflected wave-ray trajectory,but also understand the exploration area and the various waves of the time-distance relationship and energy characteristics. Forward results accurately reflect the P-wave, the wave of conversions kinematic characteristics of the offset and amplitude changes in the law, at the same time spreadsheet results also show that the method to two-dimensional and three-dimensional forward.This paper introduces iterative ray-tracing method which can be used to calculate any form of smooth interface in theory. This method has been verified by a high accuracy and speed advantages, so it can achieve any given accuracy. Based on the synthesic VSP data flow, the paper takes advantage of C program to realize the deviated well VSP forward. The forward results are consistent with theoretical analysis, which proves that the research thinking and algorithm used in this paper are efficient and correct, and can lay a solid foundation for inversion study.