Migration laws of pollutants in surrounding rock of underground oil storage caverns

The groundwater near a cavern may be polluted during the operation period of oil storage. Understanding the migration laws of oil pollutants in fractured rock mass is the base of groundwater pollution prevention and control in reservoir areas. For the sake of revealing the migration laws of oil pollutants in surrounding rock of the caverns, the migration and diffusion processes of benzene are studied by using the numerical simulation method based on the fracture-pore dual-medium model. The effects of fracture inclination angle, fracture aperture, matrix permeability and longitudinal dispersivity on the migration of benzene are also analyzed. The research results show that the migration of benzene is limited in a small range after 50 years of oil storage in the caverns, and it does not go up to the water curtain system, nor access the water body near ground surface. Under the long-term operation of the caverns, the pollution halos of the adjacent caverns can connect with each other, which will lead to cross-contamination of oil pollutants in the adjacent caverns. The vertical pollution distance of benzene is sensitive to the longitudinal dispersivity and fracture inclination angle, but weakly sensitive to the fracture aperture and matrix permeability. The maximum concentration of benzene on the central axis of rock pillars between caverns is most sensitive to the fracture inclination angle, and it decreases with the increase of the fracture inclination angle and matrix permeability, but increases with the increase of the longitudinal dispersivity and fracture aperture.