Structural Characteristics and Evolution Analysis of the North Slope of Lingshui Depression in Qiongdongnan

In order to achieve a breakthrough in the exploration of large gas field on the north slope of Lingshui Depression, based on the basin structure analysis and balanced section technique, this paper comprehensively analyzes the characteristics of tectonic pattern and fault system, and analyzes the relationship between it and hydrocarbon accumulation by using drilling and 3D seismic data. The results show that the tectonic pattern is mainly extensional and supplemented by right strike-slip, and the structural evolution can be divided into four stages: (1) fault depression period (Eocene-Oligocene), the faults are developed in the whole region and active; (2) fault-sag period (Early Miocene), elongation was weakened and the number of faults decreased; (3) the slow subsidence period (Middle Miocene), the tectonic pattern of "shelf, slope and abyssal plain" was developed, and the concave-controlling faults continued to develop; (4) the period of accelerated subsidence of the depression (Pliocene-Quaternary), the spreading effect was weakened, and the southern right-lateral tension-torsion fault zone began to be active. The tectonic pattern with alternating uplift and depression and corrsponding fault system result in high hydrocarbon generation intensity in the western steep slope zone and good matching of fault and sand body, thin hydrocarbon source in the eastern gentle slope zone, and different fault terrace transport types which result to the difference of oil and gas accumulation. It is proposed that the western F2-2 fault downslope is a favorable exploration zone for the next step, which lays a good foundation for oil and gas exploration in Lingshui Depression.