Structural features and controlling on oils in southeastern Beibu Gulf Basin

Similar to those of the middle and small basins of continental margin facies in South China, the basement of the Beibu Gulf Basin has experienced 3 evolutionary stages: rift from Paleocene to Eocene, rift to depression transition during Oligocene, and regional subsidence ever since Miocene. Influenced by the basin-forming events such as Shenhu, Zhuqiong, Nanhai and Dongsha, 4 periods of faults developed in the Fushan and Maichen sags in the southeast of the basin, resulting in 3 dominant fault systems of NE,NEE and NW directions, forming 2 tectonic layers. The faults are of flower, piled flower, petal and bush shapes, forming 4 styles including basal tilted strike-slip, basal stretch Domino, cap extensional detachment and cap sliding traction. The Fushan Sag showed an obvious asymmetric stretching process, forming NE-oriented tectonic transfer zone in the middle. The EW-oriented fault system of stage Ⅳ in the southeast of the basin controlled present oil reservoirs in the 2 sags. The nose-like structural zone in the center and the steep slope step zone in the southeast of the Fushan Sag are favorable petroleum exploration targets in the southeast of the basin.