Quantitative evaluation of fault sealing capacity and hydrocarbon migration: insight from the Liuzhuang fault in the Bohai Bay Basin, China

Hydrocarbon enrichment in faulted basins is often controlled by the activity of faults with some degree of sealing capacity. However, the rules that control the migration and accumulation of hydrocarbons in reservoirs dominated by faults are poorly understood. The Liuzhuang fault in the Bohai Bay Basin is selected for hydrocarbon migration and accumulation research. Interpretation of seismic and log data, tests of rock mechanics, and quantitative fluorescence analysis are used to quantitatively evaluate the migration of hydrocarbons. The results reveal that the Liuzhuang fault has been a long-term active fault since the Cenozoic with gradually reduced fault activity from the NE to the SW. At least four fault-bounded traps with various degrees of trap filling in the lower segment of the first member of Shahejie Formation (Es₁^L) were identified in the hanging wall of this fault. This differences in the degree of filling are related to the continuity of the smear structure that formed from the Es₁^m cap rock in the brittle‒ductile transition stage. The development degree of the smear structure, which is quantitatively evaluated by the shale smear factor (SSF) and shale gouge ratio (SGR), directly affected the fault sealing capacity. Therefore, three cases of hydrocarbon migration and accumulation, i.e., continuous smearing along the fault and complete fault sealing with SSF values of < 3, reduced continuity of the smear structure and partial fault sealing with SSF values in the range of 3–5, and discontinuous smearing and ineffective fault sealing with SSF values of > 5, were defined. The new results have implications for further exploration in faulted basins, including the Bohai Bay Basin.

Graphical abstract