Geometrical characteristics and genesis mechanism of Huizhou Sag rupture

As an important hydrocarbon-rich sag in the Zhuyi Depression of the Zhujiang (Pearl) River Estuary Basin, the geometric features and genesis mechanism of the Huizhou Sag are of key significance for hydrocarbon exploration and development. Based on high-precision 3D seismic data and seismic line analysis, we systematically analyzed the planar and geometric features of faults in different orders in the Huizhou Sag based on previous studies in the context of the tectonic evolution of the region, and explored the differences in genesis of faults in different orientations and their impact on oil and gas formation and reservoirs. Result shows that: ① The faults in the study area are mainly extensional normal faults, which can be roughly divided into three orders in size. In profile, the first-order faults are typical high-angle listric type, plate type, and sloping type, while the second- and third-order faults are mostly upright plate-type or mixed styles of Y-shaped, domino-typed, X-shaped, herringbone-shaped, and λ-shaped. On the plane, the first order faults are orientated in NE, NW, or near EW in right-handed en-echelon style; the second-order ones are mainly in NW, and third-order ones are in en-echelon style in mainly NW and near EW; ② The fault system is controlled by the succession of basement faults and the superposition of multi-staged stress field. During the Yanshanian Period, the NE–SW-oriented basement faults were reactivated to form NE and NW oriented faults. During the late rifting period, the stress field rotated, which induced the development of near EW-oriented faults; and during the tectonic reactivation period, faults were superimposed by the dextral strike-slip modification;③ NE-directed faults dominated the vertical transport in early stage; EW-directed faults drove the late reservoir formation; and NW-directed faults regulated the trap formation. This research revealed the control mechanism of multi-phase tectonic movements on the geometric features of faults, and provided a scientific basis for the future exploration and development of oil and gas resources in Huizhou Sag.