Fault-bounded traps, especially along active faults, have complicated hydrocarbon
retention and leakage mechanisms. For successful exploration studying hydrocarbon
leakage is necessary. Three traps were drilled in the Es1x submember in the hanging
wall of the NDG fault. A comparison of the actual hydrocarbon column heights and trap
heights in these three traps shows that only the NDG-3 trap is underfilled; the other
traps are completely filled. The paleo-oil column indicates that the reason for the
underfilling of the NDG-3 trap is poor retention rather than a small charge volume.
The fault sealing capacity is assessed using well and seismic data. The active fault
history and throws were measured to analyze the role of fault activation in oil leakage.
The results strongly indicate that across-fault membrane leakage is highly unlikely
to have caused the oil leakage. Instead, post-charge reactivation probably allowed
hydrocarbon leakage from the NDG-3 trap. Furthermore, elimination of the influence
of top-seal leakage also implies that post-charge reactivation is the most likely
mechanism for oil leakage in the NDG-3 trap. The critical threshold of post-charge
reactivation throw for hydrocarbon preservation and leakage is 202–208 m. When the
post-charge reactivation throw is < 202 m, upfault hydrocarbon leakage occurs with
difficulty, and hydrocarbons are preserved in fault-bounded traps. When the post-charge
reactivation throw is > 208 m, upfault hydrocarbon leakage is more likely to occur.
Although the hydrocarbons that accumulate in deep traps may be lost by fault reactivation,
this process also supplies hydrocarbons to shallow traps, which offer an opportunity
for exploration. These results can strengthen our understanding of the hydrocarbon
leakage mechanisms and locations from traps bounded by faults across the Bohai Bay
Basin. This is of particular significance in exploring for hydrocarbons and in hydrocarbon
production since seal failure is the major cause of dry wells.