Structural Characteristics of the Fault Zone and Fault-Controlled Hydrocarbon Accumulation in the Chenghai Area of Dagang Offshore

The Chenghai area is a secondary structural unit within the Qikou sag of the Bohai Bay Basin, located in the southern part of the Dagang offshore area, known for its abundant oil and gas resources. Influenced by multiple episodes of tectonic activity, the Chenghai area exhibits a highly developed fault system, which significantly impacts oil and gas exploration in the region. To investigate the structural characteristics of fault zones in the Chenghai area and their petroleum geological significance, this study builds upon previous research by utilizing oilfield drilling data and relevant seismic information. Through methods such as fault growth index analysis, structural evolution history, and examination of typical oil and gas reservoir profiles, a detailed structural analysis of fault-controlled hydrocarbon accumulation in this petroleum region was conducted. The results reveal three types of fault classifications in the study area: basal-controlled continuously active faults, buried reactivated segmented growth-connected faults, and late-stage continuously active isolated growth faults. The structural evolution is divided into four stages: the pre-Paleogene basement formation stage, the Rifting I stage of intense extensional deformation, the Rifting II stage of extensional stress reversal and intense deformation, and the post-Eocene weak extensional deformation-stable burial stage. The fault-controlled accumulation models include three types: fault-guided longitudinal accumulation, lateral sealing fault masking accumulation, and far-source step-like fault-guided accumulation. The formation of fault zones and fault-controlled oil and gas reservoirs in the Chenghai area is primarily influenced by inherited development faults, which determine the overall macroscopic distribution of oil and gas. The formation of oil and gas reservoirs occurred relatively late, with a general trend of decreased fault activity during this period, facilitating the effective accumulation and sealing of hydrocarbons.