Abstract: To accurately predict the velocity of a favorable target before drilling has always been a dream pursued by geophysics workers. For the more mature blocks, the velocity could be predicted more accurately, and smaller prediction error could be achieved, using a variety of VSP velocity, and combined with fine velocity processing results. However, there was huger error in predicting results with regards to exploration of offshore exploration wells or new areas. Such errors may arise from no exploration wells or no exploration wells at all, and the misunderstandings and problems existing during the process of velocity prediction. For instance, imaging velocity used for time-depth conversion and pressure prediction to establish velocity body could improve the accuracy of time-depth conversion. Several common problems urgently to be solved were got by analyzing some typical cases in Ying-Qiong Basin, i.e. how to judge the accuracy of re-processing velocity and how to fulfill reprocessing; there existed systematic error between logging rate and velocity spectrum velocity; velocity spectrum data were limited by its own accuracy.

Key words: velocity prediction, imaging velocity, velocity analysis, prediction erro