Water-Sealing Performance of Underground Oil Storages Considering the Capillary Effect

Water-sealing effect of underground oil storages is primarily achieved by groundwater filling the fractures. This study proposes a set of water-sealing criteria applicable to both single cavern and cavern groups considering the influence of capillary effects under different fracture apertures and roughnesses. The exponential relationship between capillary pressure and cavern geometry is further derived by using the Cahn-Hilliard-Navier-Stokes and Brooks-Corey equations. The water-sealing criterion for a single cavern is obtained by introducing the cavern geometry coefficient affected by capillary pressure. It is found that the code for design of underground oil storage in rock caverns and the water-sealing criterion proposed by Norwegian Tunnel Association serve as specific cases in the proposed criterion under varying capillary pressures. The water-sealing performance for cavern groups is further investigated considering different cavern arrangements and water curtain layouts. The water-sealing criterion for cavern groups is constructed by introducing cavern arrangement coefficients and water curtain layout coefficients. The study shows that reducing the spacing between caverns and the horizontal water curtain spacing can significantly improve water-sealing performance. The effectiveness of the proposed water-sealing criterion is analyzed through application to actual oil storage projects already in operation and under construction. The research findings provide new insights for the optimized design of underground water-sealed oil storage facilities. • An exponential correlation is proposed to quantify the fracture capillary force considering its complex geometry. • A water-sealing criterion for a single cavern is proposed considering the capillary effect of fractures. • A water-sealing criterion for cavern-group storges is proposed considering cavern group arrangements and water curtain layouts. • The reliability of the proposed criterion is demonstrated by analyzing water-sealing performance of oil storages both in operation and under construction.