Abstract
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 Eslx 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~(-2)08 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.
NSTL