Hierarchical Fault Controls on Hydrocarbon Charge, Compartmentalization and Preservation in the Nanpu 1–3 Area, Bohai Bay Basin, China

ABSTRACT Faulted rift basins commonly contain faults that alternately transmit and retain hydrocarbons, but the respective roles of master faults and small subsidiary faults are difficult to resolve in mature fields where structural relief is modest and seismic resolution is variable. This study examines the Nanpu 1–3 area in the Bohai Bay Basin using an integrated interpretation of three‐dimensional seismic volumes, coherence and dip‐guided attributes, synthetic seismograms, drilling and wireline‐log records, available core descriptions and test and production summaries. The objective is to establish how a hierarchical fault network governs charge access, trap definition, reservoir compartmentalization and preservation without treating each fault as a uniformly conductive or sealing surface. Large faults were mapped from reflector offsets, terminations and attitude changes, whereas low‐order faults were traced by combining profile interpretation with plan‐view attributes and well‐fault matches. Synthetic forward modelling indicates that approximately 10 m represents the smallest tested throw that can be reliably identified under the baseline noise condition of this dataset, rather than a universal seismic‐resolution threshold. The Nanpu 1–3 structure is organized by first‐order faults F1, F2, F3 and F8, which define the major structural compartments, and by numerous 20–60 m‐throw faults that generate relays, step‐fault packages, Y‐shaped splays and local closures. Long‐lived first‐order faults connected to deeper petroleum systems are interpreted as preferential charge‐access pathways, especially where they intersect structural highs and noses. This interpretation is additionally supported by consistent production‐fluid characteristics observed in Ed 1 reservoirs across the F1 fault zone. Preservation, however, is controlled at block scale by the geometry and termination of low‐order faults, reservoir–seal juxtaposition and the continuity of mud‐rich intervals. These low‐order faults therefore have a context‐dependent dual role: They may complete a closure and restrict cross‐fault communication, or they may connect adjacent compartments and increase leakage risk. The NPC1‐19 block provides a map‐section test of this interpretation. A low‐order fault with a near N–S strike, together with faults to the north and south, defines a coherent closure of about 0.3 km 2 , with geological reserves sufficient to support commercial development containing approximately 5.48 × 10 5 t of geological reserves; the distribution of successful wells is consistent with the mapped structural high and local compartment boundaries. The results support a practical evaluation sequence based on (1) charge access, (2) map‐section closure coherence and (3) evidence for low‐order‐fault barrier behaviour or connectivity. This hierarchical approach improves prospect ranking and reserve reassessment while keeping uncertainty associated with unresolved small faults explicit.