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Differential Hydrocarbon Differential Enrichment in Tan-Lu Fault Zone in Offshore Bohai Bay Basin


Offshore oil and gas exploration in China began in offshore Bohai Bay Basin, where Penglai 19-3, Penglai 9-1 and other large oil and gas fields have been found, and indicating promising prospect of exploration. However differential hydrocarbon enrichment is observed in oil and gas discovery. The Tan-Lu fault zone crossing eastern offshore Bohai Bay Basin could have been the cause of such differentiation. 3D seismics, wireline logs, cores, geochemical data and field survey were used to assess the relationship between fault zone activity and differential hydrocarbon enrichment in offshore Bohai Bay Basin. Firstly, a large number of structural traps were found accompanying the major strike-slip fault zone, and oil and gas generally were enriched in the fault transition zone. Secondly, late hydrocarbon accumulation was found in shallow horizons in inherited fault zone. Thirdly, the declining fault zone played an obvious role of sealing oil and gas, and hydrocarbon tended to enrich in Paleogene and buried hill reservoirs with a large number of active deep faults. Finally, the matching of fault zone activity and thermal evolution of source rock was the key factor for hydrocarbon enrichment. In addition, faulting activities affected movement of sedimentary center, deposition mode and size of reservoir sandbody. Consequently, the Tan-Lu fault zone in offshore Bohai Bay Basin could be significant in differential hydrocarbon enrichment, which has been confirmed by exploration practice.