Abstract: Velocity data is the basis of 3-D velocity field. Making comprehensive use of VSP data, velocity spectrum data and acoustic logging data can help establish a high-precision 3-D velocity field. In the process of 3-D velocity field, surface smooth processing is comparatively troublesome, and the 3-D velocity field after the gridding surface smooth processing usually holds larger storage space. The proposed block polynomial surface fitting method can effectively make up for the deficiency. The 3-D velocity field obtained from this method used in seismic data interpretation horizon calibration could provide more accurate T-D conversion relationship for the well without VSP or seismic log. On horizon calibration work, seismic data interpretation workers can also avoid blindness. This method has been applied in actual oil development and achieved good results

Key words: 3-D velocity field, horizon calibration, block polynomial, surface fitting, T-D