Abstract: The complex geological structure of the fractured rock surrounding a water-sealed cavern reservoir and the presence of an unsaturated zone of an inaccessible unsaturated zone of groundwater are the primary causes of oil leakage, leading to groundwater contamination. To evaluate the scope of oil leakage and its transport within the rock body, the impact of the water curtain system on oil transport was numerically analyzed using the pore-fracture dual medium model in a subterranean water-sealed oil cavern reservoir located in Liaoning Province, China. The geometric effects of fractures on oil transport were evaluated through the fracture’s inclination angle, degree of openness, and permeability. The study revealed that while the water curtain system could not entirely prevent oil leakage, but compared with no water curtain, it significantly reduces environmental impacts. Over a 50-year period, leakage distance remained stable at 2.20 m, with corresponding 69.11%, 80.40%, and 81.05% reductions in leakage area, maximum migration distance, and migration rate, respectively. The leakage area is maximized only when a horizontal water curtain is added, with the maximum leakage point in each condition occurring in the rock column between the caves (the area between the right and left adjacent chambers, as defined below). The presence of near-field fissures influences the spatial distribution of oil transport, with the leakage area reduced in the intersection zone with the cave reservoir. The maximum vertical oil transport distance is positively correlated with the inclination angle of near-field fissures. The oil leakage range initially increases and then decreases with increasing fracture permeability, while the fracture aperture has a negligible impact on the oil transport range. The study’s findings provide theoretical guidance for the operational design of water-sealed oil cavern reservoirs.

Key words: water-sealed petroleum caverns, surrounding rock fractures, water curtain systems, migration range