| Wan’an Basin is a typical strike-slip extensional basin in multi-plate superimposed area of southern South
China Sea. Due to the complex geological conditions and lower research degree in China, the structural characteristics of
major depressions are lack of targeted research, which limited the understanding of the potential and distribution of oil and
gas resources. Based on fine seismic interpretation, the tectonic transformation change and its unconformity
characteristics, fault systems and tectonic evolution characteristics, and the control of structures on oil and gas distribution
are analyzed in Wan’an Basin. T100 (pre Cenozoic basement interface)、T60 (Neogene bottom interface)、T40 (upper
Miocene bottom interface) are the key geological interfaces of structure and sequence in different periods with response to
regional tectonic events. The tectonic evolution of Wan’an Basin can be divided into rifting period including two episodes
(T100-T60, T60-T50), inversion period (T50-T40), and post rifting thermal subsidence period (T40-). Faults are mainly
developed below the T40 unconformity. The most developed NE, NNE faults control the tectonic pattern of Wan’an
Basin. As a basin controlling fault, Wan’an fault has strong early activity in rifting stage and weak late activity in the
thermal subsidence stage, and has strong activity in the middle, followed by the north and south in space. Under the
transformation of fault, the sag has a multi-depression structure, which reflects the characteristics of typical rift blocks and
structural evolution differences. Based on the spatial and temporal distribution of typical oil and gas fields in Wan’an
Basin, it is concluded that source rocks and their thermal evolution control the plane distribution of oil and gas fields, and
uplift belt, slope belt and reverse belt around the favorable middle sag control the spatial distribution of oil and gas fields.
On the whole, it has the oil and gas enrichment laws of preponderant accumulation in the pre bulge zone, threedimensional
accumulation in the slope zone, and compound accumulation in the central inversion zone. |
