Abstract:

The Yabei sag is a marginal sag in the northwest margin of the Qiongdongnan Basin in the South China Sea. The Yabei sag has a long exploration history, but restricted by factors such as seismic data, the exploration degree is low, there is no commercial discovery in drillings, and the implementation degree of hydrocarbon source conditions is low. In order to implement the oil and gas geological conditions of Yabei sag and promote the exploration process, using the newly acquired high-quality three-dimensional seismic data, combined with the drilled wells, analogically analyzed the seismic facies of source rocks in adjacent basins, clarified the fault, structure, sedimentary characteristics and source rock distribution in the Yabei sag, and analyzed its genetic mechanism according to the regional geological stress background. The hydrocarbon accumulation conditions and exploration deployment direction in the Yabei sag were discussed. The results show that Yabei sag is controlled by No. 5 fault. The sag is characterized by structural sedimentation of the North Fault and South overtopping. It is vertically faulted in the lower part and downwarped in the upper part. The Neogene strata are inclined to the South and few faults are developed in the basin. The Eocene middle deep lacustrine source rocks are mainly developed in the Yacheng 9 subsag, and the coal measure source rocks of the Yacheng formation are developed in the southeast of the sag. Finally, it is considered that the hydrocarbon source in the Yabei sag has the characteristics of "oil in the West and gas in the East". The western and southwest slopes of the sag and the steep slope Paleogene traps near the Yacheng9 subsag are the direction of oil exploration; however, the natural gas exploration prospect of the concave uplift and surrounding traps in the southeast of the depression is good.

Key words: oil and gas exploration potential, fracture characteristics, diapir, Yabei sag, Qiongdongnan Basin