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Control of Strike-Slip Derivative Structures on the Hydrocarbon Accumulation in the Bohai Sea, Eastern China


Tanlu Fault Zone is a giant strike-slip fault system across the eastern Bohai Sea, and it is characterized by obvious partitioned zones and multiple evolution stages, which contribute to the complex and diverse structural styles and hydrocarbon accumulation conditions. With additional extensional (or compressional) stresses, strike-slip faults are generally associated with certain oblique slip, resulting in the development of strike-slip derivative structures. In this study, mud logging, well logging, and 3D seismic data are integrated to systematically describe and distinguish the strike-slip derivative structures in the Bohai Sea. Combined with previous ideas, three categories are classified in the Cenozoic according to their locations, namely the end part, the bending part, and the stepover. Each category can be further divided into restraining and releasing classes according to the superposition ratios between strike-slip and extension (or compression) in different structural parts during different evolution stages, which lead to the differentiated local structural styles and hydrocarbon accumulation modes in different series of different areas in the Bohai Sea. It is demonstrated by comprehensive characterization of various types of strike-slip derivative structure-related reservoirs in typical zones that faults in the strike slip restraining zone have strong lateral sealing ability, and there are two key factors controlling the hydrocarbon enrichment and accumulation, namely the sufficient oil supply and the good match of the timing of fault activity and hydrocarbon expulsion. The strike slip releasing zones in the end and stepover of faults are favorable for oil enrichment because of the low potential, reservoirs in which are dependent on the mild fault activities in the later stage and the strong sealing capacities of the strike-slip faults. Based on analysis of accumulation conditions of middle-huge oil and gas fields found in the Bohai Sea, it is concluded that strike slip restraining structures are more favorable than strike slip releasing ones, while the bending part is optimum, the stepover followed and the end part is the worst of ones. It is crucial to clarify the styles, temporal distribution of the strike-slip derivative structures and their control effects on hydrocarbon accumulation in the Bohai Sea, which can promote the oil and gas exploration and provide references to study the Cenozoic tectonic dynamic in the eastern China.