Segmented difference in fault activities and combination pattern of strike-slip fault zones in Changdi area, Bohai Bay Basin

The strike-slip fault zone in Changdi area, Bohai Bay Basin belongs to the derivative structural zone on the east side of Tanlu strike-slip fault zone, which is rich in oil and gas resources. During the sedimentary period of Shahejie Formation, the fault zone underwent a multi-stage superimposed transformation of extension and strike-slip. The dynamic mechanism of fault segment activities and its control mode for differential accumulation of oil and gas have not been systematically revealed. Three-dimensional (3D) seismic data, drilling data, and core logging data were analyzed, and seismic fault and horizon interpretation, seismic attribute analysis, fault growth index, and other methods were employed to study the fault properties, activity history, combination characteristics, and segmented differences of strike-slip fault zones in Changdi area during the sedimentary period of Shahejie Formation, so as to deepen the understanding of the segmented development characteristics and oil and gas accumulation rule of the associated strike-slip faults in the background of large strike-slip fault zones. According to the research, seven fault groups including the tension-torsion fault group of the main fault, compression-torsion fault group of the main fault, and differential extensional strike-slip fault group were identified in the strike-slip fault zones in Changdi area, and six structural styles including forward fault-step group, reverse fault-step group, Y-shaped and anti-Y-shaped fault group, horst type, graben type, and subduction reverse fault group were observed in the section. On the plane, it could be divided into five sections: branch tail end, tail end, compression-torsion overlapping area, tension-torsion overlapping area, and main displacement area. Among them, the fault activity of the southern branch tail was weak, which was manifested as the tensile horsetail structure, and the stress release was concentrated on the northern branch tail. The poor sealing property of the two sections leads to oil and gas escape. The compression-torsion overlapping area had strong fault activity, flower-like structure, gentle lower section and steep upper section, and good sealing properties, which are conducive to oil and gas accumulation. Brittle conjugate faults and reverse fault-step structures were developed in the tension-torsion overlapping area. The main displacement area was S-shaped due to the opposite tension-torsion and compression-torsion sections, with the strongest fault activity and strong section sealing in the compression-torsion section, which was conducive to oil and gas accumulation, while the tension-torsion section had strong communication, which was conducive to oil and gas migration, and with echelon faults and subduction reverse faults developed.