VARYING VELOCITY MAPPING TECHNOLOGY AND ITS APPLICATION TO WESTERN PART OF THE SOUTH CHINA SEA

The research area is located to the east of ZhusanA depression in the western Pearl River Mouth Basin. It is a low-amplitude anticline with steep extensional faults and characterized by large deference of P and S waves. In previous researches, migration velocity was used for time-depth conversion, but the precision and density are beyond the standard to meet the users' demand from oilfields. The authors applied the mapping technology of varying velocity and velocity inversion to map the area. At first, space migration was carried out for the data after prestacking time migration interpretation and a zero-offset time domain layer data generated. Then stacking velocity was applied to the internal velocity inversion for each layer. The varying velocity structural map was thus compiled with the method of 3D space ray tracing. The methods can avoid the errors caused by Dix formula.