Abstract:

The Gaoyou sag in Subei Basin is rich in oil and gas resources. The types and distribution of discovered oil and gas reservoirs are closely related to the fault development characteristics and evolution. In this paper, the basic characteristics, types, and active periods of faults in the Gaoyou sag are studied with high-precision 3D continuous seismic data, and the fault systems are further divided to elucidate the controlling effect of fault systems on hydrocarbon accumulation. The results show that there are four types of fault systems in the sag: Late Cretaceous-Paleocene normal fault system, Eocene Dainan normal fault system, Eocene Sanduo transtensional fault system and long-term active fault system. There are three periods of intensive fault activity: the Late Cretaceous-Paleocene dispersed deformation under the NW-SE extensional stress field, forming the ENE-NE extensional faults. The concentrated deformation occurred in the NW-SE extensional stress field in the Eocene and formed the NE-directed extensional faults. During the Eocene Sanduo stage, extensional deformation occurred under the near N-S extensional stress field, forming late tensional faults near EW direction. Long-term active faults are characterized by multiphase active faults. The long-term active fault system carries oil and gas vertically. The normal fault systems of Upper Cretaceous-Paleocene and Eocene Dainan formation have good lateral sealing conditions, and facilitated the formation of various fault trap types. The Eocene Sanduo normal fault system may have destroyed cap traps and was not conducive to oil and gas preservation. The rolling anticline trap and transverse anticline in the hanging-wall of the long-term active fault in the deep depression zone. The fault block trap in the footwall of the fault between the sub-points of the long-term active fault in the fault step zone, and the tilted fault block trap in the eastern slope of the slope zone are favorable targets for oil-gas migration and accumulation.

Key words: fault system, activity period, trap, migration, fault reservoir control, Gaoyou sag