Effect of capillarity in a fractured medium on water-sealed properties: a theoretical and experimental investigation

Abstract

Underground water-sealed oil storage caverns are typically built in crystalline rock masses of good quality, and the water-sealed effect is realised by filling the fractures with water. Theoretical equations for the water-sealed properties of a fractured medium were established in this study considering the capillary force. The capillarity in the fractured medium and its effect on the water-sealed properties were investigated using a single-fracture model test method. The dynamic variation in the water–oil displacement process in a fracture was described by varying the fracture width and the liquid height in the two tanks. An index was introduced to characterise the degree of water–oil displacement quantitatively. The results show that the capillarity in the fracture thus improves the water-sealed properties of underground caverns. The current water-sealed criterion and empirical formula are relatively conservative. The water–oil displacement process in the fracture is controlled by the capillary fracture water height and the oil height in the liquid tank. The variation in the capillary fracture water height corresponding to a unit of oil injection (N) can be used to characterise the water–oil displacement process quantitatively. The results of this research can provide a reference for studying the effect of the capillarity of a fractured medium on the water-sealed properties of underground oil storage.