Velocity-Depth Model Building Method And Its Application To Pre-Stack Depth Migration

Migration imaging is one of the major development directions of seismic exploration technology for oil and gas. Pre-stack depth migration is inevitably choice for the imaging of complex structures due to its advantages. However, pre-stack depth migration is only valid and can give correct image under accuracy velocity-depth model. Now the application of pre-stack depth migration is not universal, because of the inaccurate velocity-depth model. So velocity-depth model is right or not to become a key of the pre-stack depth migration. As we known, velocity-depth model is determined by two factors: interval velocity and depth of layers. So we believe that a good migration result depend on a reasonable velocity and layer depth.First of all, this paper introduces some basic concepts of migration and its development, and some ways to build velocity-depth model. Furthermore, we analyze pre-stack depth migration workflow which is commonly used currently in actual production, and point out its unreliability: when we building velocity-depth model, the interval velocity and layer two factors change simultaneously. To address this problem, we started from the theoretical model of forward modeling, emphatically discussed the effects of the interval velocity and layers on the pre-stack depth migration, to find the relationship between the two factors. Based on the testing results of two factors, we optimized iterative process of pre-stack depth migration, and then obtained a new one. Then we used DIX formula and Constrain Velocity Inversion to calculate the initial interval velocity, and analyzed the effect of the two methods in pre-stack depth migration imaging. Finally, we obtain a good depth migration imaging when new pre-stack depth migration process is applied to 2D steep structures model, 2D and 3D real data.