Water seal safety evaluation of multi-period adjacent underground caverns based on the discrete fracture network

ObjectiveMany large-scale underground caverns in China are constructed in multiple phases, and the expansion of underground caverns may have a certain impact on the seepage fields of adjacent operating caverns of the same type, potentially leading to a series of safety incidents such as oil and gas leakage. Therefore, ensuring the safety of the water seal after expansion is of critical importance. Methods In this paper, to address this problem, the geological conditions and fracture distribution characteristics of the reservoir site area were analyzed based on a large underground cavern expansion project. Considering the joint dense zone connecting the two-stage caverns, and based on the field hydrological test results, the equivalent aperture of the fractures was inverted. A simplified model of the two-stage underground caverns was then established using the discrete fracture network (DFN) approach. The water seal safety of the expanded underground caverns was studied, along with the influence of the expanded caverns on the water seal safety of the operating caverns. ResultsThe research showed that the expanded caverns had no effect on the water seal safety of the operating caverns, but the joint dense zone seriously affected the water seal safety of the expanded caverns. Through the study of the factors influencing the water seal safety of the adjacent operating caverns caused by the cavern expansion, it was determined that the minimum safety distance between the caverns was 200 m, and when the vertical and horizontal water curtain pressures were set to 0.4 MPa, these settings guaranteed the water seal safety of both the expanded and operating caverns. Therefore, for large-scale underground cavern expansion projects, the joint dense zone is the key factor affecting water seal safety. Ensuring a minimum safety distance and appropriate water curtain pressure can effectively ensure the safety of both the expanded and operating caverns. ConclusionThe results provide a theoretical basis for addressing water seal safety problems in the expansion of large-scale underground caverns.