Characteristics and evolution of fault structures in Lengquanting area of Xihu Sag

The Lengquanting area is a major hydrocarbon exploration area of the Xihu Sag, and the fault structures in this area are highly developed due to multi-stage tectonic movements, and plays a very important role in controlling the sedimentary tectonic evolution and hydrocarbon accumulation in the basin. Based on the detailed structural interpretation of the latest 3D seismic data in the Lengquanting area of the Xihu Sag, we analyzed systematically the fault structure types, geometric characteristics, and genetic evolution of the area to understand the development mechanisms of faults, and the key con-trolling factors of hydrocarbon accumulation. Results show that the faults in the area are mainly normal faults and strike-slip faults. There are a large number of faults and their activities are characteristic of zoning and stratification in space. Affected by the regional stress field, the fault structure of the study area has experienced five major stages: ① Fault depression period (Paleocene-lower Pinghu Formation deposition period), with three episodes of strong torsional-tensile activities; ② Fault-depression transition period (middle-upper Pinghu Formation deposition period), with inherited tensional-torsional activities of large and medium-sized faults; ③ Initial depression period (Huagang Formation deposition period), with inherited weak torsional-tensile activities of the main faults; ④ Stable depression period (Yuquan Formation-Liulang Formation deposition period), with inherited weak extensional activities of the main faults in the western slope break zone and the main fault in the area; ⑤ Regional subsidence period (from Santan Formation deposition period to the present), with weak extensional activities of the main faults in the western slope break zone caused by shear stress.