Correlation Between Fracture Systems on Outcrop and Uplifted Basement Blocks in Sedimentary Basins: A Case Study of the Uplifted Basement Block in the Cuu Long Basin

Predicting fracture architecture away from wells remains a major challenge in crystalline basement reservoirs because hydrocarbon storage and fluid flow are controlled predominantly by heterogeneous secondary fracture networks. This study evaluates whether an exposed granitoid block can provide a useful structural analogue for a deeply buried fractured-basement reservoir through integration of field fracture mapping at Ke Ga, borehole image and conventional well-log data from Well BH-415 in the Bach Ho field, multi-mineral petrophysical modelling, and seismic attributes in the Cuu Long Basin, offshore Vietnam. Three principal fracture populations were identified at Ke Ga, dominated by a NNE–SSW-oriented set striking approximately 20–30° and representing about 57% of the mapped fractures. The BH-415 basement contains vertically variable NNW–SSE, NNE–SSW, NE–SW, and NW–SE fracture trends associated with contrasting degrees of brecciation, alteration, and secondary pore development. The highest-quality fractured intervals exhibit net secondary porosity of up to approximately 6.6% and net permeability exceeding 1100 mD. Cross-scale comparison reveals partial rather than one-to-one structural correspondence: the dominant NNE–SSW Ke Ga population is compatible with NNE–SSW to NE–SW trends in BH-415, and a NW–SE population occurs in both datasets, whereas other subsurface fracture trends lack clear outcrop equivalents. RAI-derived seismic attributes further show spatial consistency with structurally heterogeneous intervals identified at the well. These results demonstrate that fracture orientation alone is insufficient to predict reservoir quality and that outcrop observations should be used primarily to constrain plausible structural architectures rather than to transfer petrophysical properties directly to the subsurface. The integrated workflow provides a conservative cross-scale framework for characterizing heterogeneous fractured crystalline basement reservoirs and evaluating the applicability of surface structural analogues in subsurface exploration.