Tianjin Branch of China National Offshore Oil Corporation (CNOOC),Tianjin 300452, China

Varying degree of velocity anomalies has been appeared in Shijiutuo uplift in Bohai Sea, which are mainly demonstrated in the inconsistent between seismic interpretation and the actual drilling depth. In this paper, QHD33-1S area is taken as the example. First of all, the main reason that causes the velocity anomaly phenomena is the effect of sand-formation ratio by forward model analysis, and then technical approaches to improve the accuracy of the velocity field and the degree of understanding of anomalies are further explored, resulting in more precise determination of horizontal variation trend of the velocity in QHD33-1S area. Consequences of actual applications indicate that through the accurate analysis of the velocity anomaly, we can not only realize the fine description of low-amplitude structure, but also the effective prediction of the hydrocarbon-bearing properties of the reservoir. Meanwhile, the results also have certain significance to the other low-amplitude structures in Bohai Sea.