Effects of Multistage Paleostress Reorientation on the Sealing Capacity of Fault Zones: A Case Study of the Huizhou 19‐6 Area, Pearl River Mouth Basin, Northern South China Sea

ABSTRACT The Paleogene formations in the Huizhou 19‐6 area are dominated by high sand‐content strata. Fault development in this region is controlled by multiple episodes of tectonic activity, forming a structural pattern of ‘initially wrench‐dominated, followed by extensional deformation’. Under these conditions, faults play a dual role as both conduits and seals during hydrocarbon migration and accumulation. Accurate assessment of fault sealing capacity is therefore critical for understanding deep reservoir formation patterns and optimizing exploration well placement. Traditional evaluation methods based on shale smear zones are unsuitable for sand‐rich formations, as they fail to capture the mechanical essence of fault sealing. Nevertheless, field observations confirm that faults in these sand‐rich layers can exhibit strong sealing properties. This study adopts a geomechanical approach focused on faults within the high‐sand‐content strata of the Huizhou 19‐6 area. We integrate three‐dimensional (3D) seismic data, geomechanical experiments, imaging logging data and finite element numerical simulations to construct a geomechanical model for fault zone sealing capacity evaluation. Particular emphasis is placed on how multistage stress reorientation affects fault sealing behaviour. The results show that repeated changes in in situ stress orientation alter the shear and normal stress states along fault planes. In sand‐rich formations, this leads to stronger sealing in northwest‐trending faults than in nearly east–west‐trending faults. In the absence of stress reorientation, sustained extensional forces increase the slip tendency index of northwest‐trending faults, thereby weakening their sealing capacity. These findings provide theoretical support and technical guidance for deep hydrocarbon exploration in the Huizhou 19‐6 area and similar structural settings within the Pearl River Mouth Basin. They also offer significant reference value for trap evaluation and well placement in offshore deep clastic reservoirs.