Abstract：The time to depth conversion is needed when using drilling data and well logging data to calibrate seismic horizons,to determine the depth of the horizons and to convert seismic t0 contour maps to structure maps in depth.The accuracy of the time to depth conversion depends on the accuracy of the velocity.The velocity field for time to depth conversion is usually acquired by using the H-T function method,inter-well mathematical interpolation method and DMO velocity field method,but the accuracy of the velocity field acquired by the three methods can not meet the need of EP tasks.It was shown in this paper that the velocity field which was based on ray tracing CMP coherent velocity inversion technique was successfully applied in JZ251 area in Bohai Oil-field.The CMP coherent inversion velocity error analysis indicates that the error is a stable and global error and it can be removed by corresponding correction.
